I've been working on this for a while, and they're NOT COMPLETE. Caution: this is a long ass post.
If anyone thinks of other things, let me know and I'll add them to the lists.
Offensive Threats:
Honchkrow
This guy can run Choice Band, Choice Scarf, Mixed or Physical All Out Life Orb, or Bulky Sub, and all of them are extremely strong. Even a Nasty Plot set is probably viable for shock value alone. My personal favorite is the Bulky Sub Krow, but personal preference is for a different discussion. This guy's Brave Birds are extremely strong, and you have to watch out for his Sucker Punches as well. The best stop to this is Eviolite Rhydon or Rhyperior, who laughs at the Brave Birds and doesn't care about Sucker Punch as he attempts to use Stone Edge. Superpower does decent damage as it is on a lot of Honchkrow's sets, but it's not even a 2hko on Rhyperior and DEFINITELY not on that Eviolite Rhydon. Honch usually isn't that bulky (unless its the sub set), so priority can do a number on it in the forms of Mach Punch from various mons in the meta. Honch is also quite slow so it can be revenge killed by most speedy things that aren't afraid of Sucker Punch, which makes Primeape an excellent revenge killer (but obviously you can't switch him into a Brave Bird). A good partner for Honchkrow on your own teams is definitely a rapid spinner, as Honch does not enjoy Life Orb damage + Stealth Rock damage + Brave Bird recoil, which can severely hamper his sweep. Claydol has decent synergy with Honchkrow, being immune to electric and resisting rock attacks. Claydol can also work to set up his own Stealth Rocks to hamper the opposing team.
The Quiver Dancers - Venomoth, Lilligant
These are the two most viable Quiver Dancers in the tier, but really anything with Quiver Dance can cause havoc (lol Butterfree). Both of these function mostly in the same way and both have merits to being used over the other. Regardless, Quiver Dance boosts speed, special attack, and special defense, and after one or two of these you really can't expect to be killing them with a special move. Furthermore, both of these Pokemon commonly run Sleep Powder to eliminate their counters (which there are not very many of). Venomoth has Tinted Lens which ignores resistances and makes its Bug Buzzes absurdly hard to stop, and Lilligant has Own Tempo Petal Dance or Giga Drain for either massive damage or recovery to help increase the longevity of their sweeps. They are both perfectly capable of running bulky RestTalk sets and all-out offensive sweeping sets, and both are extremely powerful in this metagame. The best way to stop the sweeping sets is to inflict them with a status (paralyze or burn, since Venomoth can't be toxiced) or hit them with a speedy scarf user before they accumulate multiple Quiver Dances. Scarf Typhlosion outspeeds Venomoth after +1, but I don't think he outspeeds max speed Lilligant (correct me if I'm wrong. Either way, Lilligant usually won't do too much to Typhlosion). Typhlosion can then attack with a strong super effective fire attack and decimate the dancers. The Rest Talking sets are much more difficult to stop, and you have to be on top of your game against them and knock them out before they start getting too powerful. You can weaken them so they use Rest and hope the Sleep Talk doesn't hit their attacking move while you try to pummel them with a Brave Bird or something, but that can be very risky at times. Basically you just can't let the RestTalking sets get set up. In the realm of walling these Pokemon, Eviolite Munchlax is a pretty sure bet, and he can phaze both out with Whirlwind. You only have to be wary of Sleep Powder. Moltres can sometimes wall them depending on the set, but if people catch on to my Lilligant set that uses HP Rock, Moltres will definitely not be walling anytime soon. Venomoth likes a Rapid Spinning partner since she has a Stealth Rock weakness, and Lilligant appreciates a lack of Toxic Spikes on the field since she is very susceptible to those.
Yanmega
Pretty much the biggest menace in the entire tier. He is capable of running two extremely powerful sets: a speed booster, and a SpecsLens set. Both sets are incredibly powerful, and if you don't have the right check/counter on your team, you WILL get swept. The Speed Boost set uses Protect to get a boost and then will be outspeeded by basically nothing, and Yanmega will be free to fire off Bug Buzzes and Air Slashes (and then a third move which is up in the air. Giga Drain is the best option, imo). Yanmega has a high special attack stat, so it's very hard to wall this guy. The SpecsLens set is, imo, more devastating. With Tinted Lens, nothing resists Yanmega's Bug Buzz, so it's nearly impossible to take. The best counter to both sets is Eviolite Munchlax, who can fire back a Rock Slide or simply phaze Yanmega out. Rotom-S is a good stopper of the Speed Boost set, but can't take the SpecsLens's Bug Buzzes. Electrode is immune to Bug Buzz, resists Air Slash, and fire back with super effective electric attacks, but can't take HP Ground if that's Yanmega's third coverage move. Specially Defensive Gastrodon can tank a few hits as long as Yanmega isn't running Giga Drain, but is not going to enjoy Specs boosted Bug Buzzes. Basically, the Speed Boost set has a few decent checks, but there really isn't any counter to the SpecsLens set. In terms of teammates for Yanmega, once again a spinner is appreciated, but most people run Yanmega in the lead position so the 4x Stealth Rocks weakness can't be exploited.
Sharpedo
Sharpedo is another Speed Booster that wreaks havoc in this tier, and is even more dangerous in the rain. The most threatening set is his Mixed set, with Surf/Crunch/Ice Beam/Protect, of which there aren't a ton of counters too. The best answer is Eviolite Ferroseed, who walls basically any Sharpedo set to death. Tangela doesn't have a problem either if Sharpedo doesn't have Ice Beam, but it often does have Ice Beam which poses a problem. Blastoise is a great tanking check, and can even burn Sharpedo with Scald to severely hamper its efficiency. Gastrodon is another excellent answer, as he is immune to water attacks and is bulky enough to take the other attacks Sharpedo can throw at him. Sharpedo is also weak to fighting priority, which makes Hitmonchan or anything else with Mach Punch a pretty good answer.
Durant
The best way to stop Durant is to just hit it with basically anything. Seriously, it is that frail. However, if you're facing a good Durant player that eliminates your priority users and scarf mons, you're in for some hurt, because Hone Claws Hustle Durant will slaughter basically anything in the tier. Iron Head/X Scissor/Stone Edge are its usual coverage moves, and are more than enough to decimate almost anything in sight. Eviolite Gligar is a great answer, as he can tank a hit and Roost of the damage with no problem, but he can't do a whole lot back, and if Durant tries to set up another Hone Claw or two, Gligar will be in serious trouble. Most Scarf Pokemon, like Scarf Typhlosion, will have no trouble KO'ing Durant, as Durant is incredibly frail.
Rhydon/Rhyperior
Rhydon and Rhyperior are serious heavy hitters in this tier. Earthquake and Stone Edge are the only coverage moves they really need to achieve excellent coverage. The common sets are Rock Polish, SubSD, or a simple tank that sets up Stealth Rock and Phazes (some sets might even try to use both Rock Polish AND Swords Dance. If that player manages to set this up on you...good luck. You'll need it). Every set Rhyperior uses is walled by Eviolite Ferroseed, Tangela, and Gligar (if you haven't noticed, it's good to run one of these three on your team). One of the best ways to take care of any Rhyperior set that's not the Rock Polish set is by simply using something faster than it (which is basically everything) that can exploit one of Rhyperior's 4x weaknesses (water and grass). Blastoise is a great tanking answer, while Sharpedo basically uses Rhyperior as set up fodder. The differences between Rhydon and Rhyperior are simply a matter of more defenses versus leftovers recovery. It's really the same issue as Blissey versus Eviolite Chansey. Players that plan on using one of these Pokemon as a utility Pokemon or a Rock Polisher should use Rhyperior, but the SubSD is probably more potent on Rhydon as he can tank almost any physical attack in existence, and most won't even break his sub.
Galvantula
Another bug type! (Noticing a pattern?) Galvantula's best set is his Choice Specs set, where he uses Compound Eyes to boost his accuracy so he can fire off Thunders all over the place. Some players use Expert Belt to give the allusion that he's holding Specs to take a player by surprise, so take that into account. Usually the coverage moves used are Thunder/Bug Buzz/Energy Ball/HP Fire, and these moves provide excellent coverage in this metagame. Once again, Munchlax is the premier special wall in the tier and can tank Galvantula's hits fairly well. If our electric spider is choiced, you can switch around to take resisted or immune hits, such as switching in Rhyperior on a Thunder. If you're putting Galvantula on your team, you want a spinner so you can keep bringing in your spider to fire off those Thunders since Galvantula is susceptible to every type of entry hazard.
Alakazam
A menace of destruction that almost no one uses (I used him to get up to top 20 on the ladder). The best set, in my opinion, is SubCm with Psychock and Focus Blast. With this, Alakazam can use his insane speed to set up a quick Sub and get fast Calm Minds in until he isn't even touched by Special Attackers. Psyshock is used over Psychic to make this a Cresselia killer; most Cresselia like to try and set up Calm Minds alongside you, thinking it's going to be a stalemate in the end. But then you surprise them by hitting them for over 50% with a +6 Psychock. Still, considering how common bug types are in this tier, Alakazam gets faced with some tough situations quite often. Things with strong priority like Choice Band Entei can knock Alakazam out of commission. Frankly, physical attackers that are faster than Alakazam in general are a bit of a problem. Yanmega hurts Alakazam bad after it gets some Speed Boosts and the ability to outspeed Zam.
Rain
This is very general, because there are multiple viable rain sweepers. Rain as a whole is very powerful and arguably broken in this tier. You will often see Electrode setting up an 8-turn monsoon of destruction where Shell Smash Omastars, Ludicolos, and Swords Dancing Kabutopses rip our face in half. There aren't many good answers to this besides trying to stall out the rain. Rain Dish Blastoise does well against everything but Ludicolo. Running a Rain Dish Ludicolo on your own team can help wall the sweepers. Pokemon with the Cloud Nine ability can help by getting rid of the rain (so Golduck and Lickilicky I think...nothing else <_<). Eviolite Ferroseed and Tangela wall the offensive rain sweepers but are in serious trouble if they face anything special. If you survive the initial rain onslaught, try to KO the Pokemon that set the rain up before they can get it off so you don't have to feel the pain again. Another decent answer to rain is Sharpedo, who can use your opponent's rain to fire off boosted Surfs, and can let Speed Boost accumulate until he's faster than the rain sweepers (Yanmega is in the same boat here to an extent, and can use Giga Drain and Bug Buzz to kill off Omastar, Kabutops, and Ludicolo).
Entei
Entei is capable of running excellent sets in both the physical and special categories, make him very unpredictable and very hard to wall. His Choice Band set is very powerful, and you'll often get hit with STAB Flare Blitzes and priority in the form of Extremespeed. It's hard to take these hits, and your best bets are Eviolite Gligar, Cresselia, or Gastrodon. The Calm Mind set is harder to wall, and can run either Sub or RestTalk to eliminate the possibility of status and eventual damage. Munchlax doesn't have much of a problem taking Entei's hits and can whirlwind him out. Cresselia can Calm Mind alongside Entei and the CM battle will end in a stalemate. Gastrodon will win against any Entei set almost every time unless Entei is using something bizarre like HP Grass.
Porygon-Z
One should always make sure they're capable of taking on Porygon-Z...otherwise, you're in for a miserable time of getting slaughtered by Adaptability or Download boosted special attacks. Porygon-Z is almost always holding a scarf or specs, but don't completely dismiss the possibility of a Nasty Plot set, because that as completely viable as well. Porygon-Z is basically the most powerful special attacker in the tier, but he is also quite frail, so he takes on the "glass cannon" persona. Having a priority user such as Hitmonchan to kill Porygon-Z is probably the most reliable way of getting rid of it, but you'll have to revenge kill because Hitmonchan is never going to come in on a specs or scarf Tri-Attack and live. Munchlax doesn't take a whole lot from P-Z's attacks, but he doesn't have any recovery so he can't exactly come in all the time. Specially Defensive Aggron has a 4x resistance to Tri-Attack and only has to worry about whatever Hidden Power Porygon is running.
Swellow
Swellow is extremely dangerous in this tier, as he can get through some of the commonly used physical walls such as Tangela or Blastoise. With Guts, STAB Brave Bird, and a very nice speed stat for RU, Swellow can wreak a lot of havoc here, dealing colossal damage to basically anything that's not Rhyperior. The good news is that Swellow's sweep will be very short; between Stealth Rock and the toxic or burn put onto itself for guts, Swellow should die pretty quick, but that's not before is murders half your team. As said before, Rhyperior chuckles as Swellow tries to break through with a resisted Brave Bird and can OHKO back with Stone Edge. Priority users can pound on Swellow's weak defenses in hopes of making it die quicker. Aggron laughs at anything Swellow can ever hope to throw at it and can throw STAB Stone Edges back at it. Cofagrigus can switch in and tank a Brave Bird and give Swellow Mummy, which takes away her Guts boost and makes her significantly less effective.
Primeape
Primeape has the honor of being probably one of the most viable fighting types in a tier that has a LOT of decent fighting types. Primeape sports a decent 95 base speed, 105 attack, and a great ability in Vital Spirit that prevents him from going to sleep. All of this works together to make Primeape a fairly potent answer to things like Venomoth when holding a scarf, because Primeape outspeeds Venomoth at +1, is immune to the sleep, and resists Bug Buzz. Primeape can then hit Venomoth with a super effective Stone Edge or Fire Punch for big damage and a KO. Outside of being a revenge killer and sleep absorber, Primeape doesn't have a whole lot of utility in this metagame though. He will never be able to touch Tangela, and other common walls such as Cofagrigus and Cresselia laugh at everything Primeape tries to throw at him (besides U-turn on Cresselia). A set of Close Combat/U-turn/Stone Edge/Ice Punch has worked fairly well for me, and has its merits as a revenge killer in this tier.
SmashPass
SmashPass is a horribly strong strategy that was even nominated for banning in OU, which probably gives you an idea of how powerful it can be in RU. While there aren't as many solid support Pokemon to help the strategy (damn Espeon), it can still be very viable and very destructive in the right hands. There are a couple worthy users of Shell Smash and Baton Pass, but the Pokemon you'll see doing it most often is Gorebyss. Gorebyss has very mediocre stats, but if you allow it to get off a Shell Smash and you don't have strong enough priority to kill it, you're likely in for some hurt, as it's probably going to pass to something insanely powerful such as Rhyperior, and once that happens...there really isn't much hope for you. The best answer to SmashPass is to stop the pass before it happens. When Gorebyss comes in, hit it as hard as you can, as its defenses aren't great and you can hopefully KO it before the destruction begins. Phazing is also a solid option as long your opponent hasn't used something like Ingrain Smeargle. If the pass does get off to something like Rhyperior, you'd better pray you can burn it or something, otherwise it's game over.
Typhlosion
Typhlosion sits here as one of the best revenge killers in the tier and sports some of the most absurdly powerful attacks imaginable with a Specs set. Really, the most viable sets are Scarf and Specs, but a SubPetaya set could be possible and extremely destructive in the right hands. Regardless, you'll most often see a Scarf set with something like Fire Blast/Eruption/Hidden Power ?/Focus Blast, and that set grants him some great coverage in this metagame. Personally, I'd say Hidden Power Grass is the best choice, so you can revenge kill any Rhyperior, even if it's a Rock Polisher at +2. Eruption at full health is Typhlosion's most powerful attack, and is easily capable of OHKO'ing things like Venomoth with a Quiver Dance under its belt. Typhlosion's great speed lets it outspeed many threats in the metagame even with boosts to their speed, even things like Yanmega with a boost. Typhlosion's specs set takes away this revenge killing ability for the most part in exchange for an insane amount of firepower. Specs+Eruption at full health = incredible damage, even against things like Thick Fat Munchlax.
Gallade
Gallade is a fairly capable physical sweeper in RU, capable of boosting his attack (and defense if using Bulk Up), and sweep with good coverage and a heck of a lot of power. Gallade's most dangerous set would be a set decently similar to Conkeldurr's popular set in OU, where you'll see Bulk Up, Drain Punch, priority (Shadow Sneak in Gallade's case), and then a coverage move, which would probably be Psycho Cut for Gallade, giving him an extra STAB and helps out the already perfect coverage on the set between Drain Punch and Shadow Sneak. Gallade is quite powerful with this set, however he isn't too fast, and can run into trouble when quick, powerful revenge killers come to take him out. Gallade's excellent special defense could potentially let him live against things like a Specs Galvantula's Bug Buzz, but he's going to have trouble against something like a Swellow's Brave Bird even with a Bulk Up or two, so the best way to take out Gallade is with his decent frailty and a strong super effective attack.
Sceptile
Swords Dance and Unburden. I'll admit I didn't come up with the idea, I only tried it out because reachzero mentioned it a few times, but my God, it is powerful. Sceptile is capable of running either physical or special set and he does both extremely well, and has enough speed to outspeed a TON of things in this metagame. You can go Specs, SubSeed, Scarf, whatever, but the most potent sweeping set is definitely SD Unburden. The set in particular I've been using is Swords Dance/Leaf Blade/Acrobat/Earthquake, with a Flight Gem equipped. Set up a Swords Dance, throw out an extremely powerful Acrobat, and then you have very high attack and a speed stat that's over 700, so you won't be outsped by anything in the tier unless it has +3 or 4 in speed (suck on some of that, Yanmega!). From there, it's an easy road to a sweep, because you'll be absolutely unstoppable, because really nothing can stop this Sceptile once it has set up properly. Something like max defense Steelix can tank a hit and phaze out Sceptile. Pokemon with strong priority can pound Sceptile's lackluster defenses in hopes of KO'ing it before Sceptile unleashes it's wrath.
Manectric
Manectric is a fairly good user of Scarf/Specs and competes for a spot with Galvantula in most cases. The advantage Manectric has are Switcheroo, which is basically like Trick and can effectively screw over almost any wall, and the ability to use fire attacks such as Overheat. However, Galvantula can use bug attacks and has Compoundeyes so he can run more powerful moves like Thunder. Either way, both are capable of punching holes in your team, and it just depends on what you're looking for in an electric type special attacker.
Defensive Threats:
Cresselia
The queen of this tier (the king is Yanmega. They're a cute couple). Anyway, Cresselia is insanely good in this tier. Her defenses are through the roof, and her common sets are Rest or Sub with Calm Mind, and a simple support set. On her calm mind sets, the best way to take her out is with a very strong, super effective physical attack, because once she starts setting up, your special attacks will not be touching her at all. Status doesn't work since the common sets are Sub and RestTalk. A good Cress player won't attempt a final sweep until it's their final Pokemon, so basically you just have to try and hit it as hard as you can or you're absolutely screwed. A strong pursuit user like Honchkrow can smack it around a bit. Fellow calm mind users can set up alongside Cress and initiate a stalemate. CM Alakazam with Psychock is an excellent Cress killer because Psychock will do hefty damage with +6 special attack while Cress won't be able to touch you. If you're putting Cresselia on your team, you really don't need any support for her at all, as she can sweep on her own incredibly well. Just try to knock all bug types out of commission before attempting your sweep.
Tangela
Eviolite Tangela is probably the best physical wall in existence. Sporting a defense over 500 and an HP stat in the mid 300's, Tangela laughs at any physical attack you can muster, even tanking a Flare Blitz from Entei and striking back with something like Leech Seed or Sleep Powder. Tangela also has Regenerate, which actually allows him to recover some of his HP, unlike other Eviolite users. Tangela's best set by far is Leech Seed/Sleep Powder/Knock Off/Giga Drain. With that set, you can completely screw with any physical attacker by Knocking Off their Life Orbs, putting them to sleep, or leech seeding them for recovery. Knock Off also completely ruins fellow Eviolite users or things that rely on Leftovers to survive for a long time, making it an excellent move to put on Tangela. Sleep Powder is an obvious useful move on any team, and Giga Drain is Tangela's most preferred move for attacking, as it gives him recovery and a decent way to put a dent in powerful attackers such as Rhyperior. Unfortunately, Tangela can not take any special attacks at all, and will fall quickly to Flamethrowers and Bug Buzzes, making it essential to have some sort of specially defensive threat on your team as well.
Munchlax
Eviolite Munchlax is a specially defensive monster. He is one of the best answers to Yanmega, Moltres, Omastar...the list goes on. With an Eviolite, Munchlax sports something like 440/440 special defenses, so he is nearly untouched by most special attacks. With Frustration/Rock Slide/Toxic/Whirlwind, you have plenty of options against opponents like Yanmega. Rock Slide does something like 80% to most Yanmegas, while Bug Buzz will do very little to Munchlax here, allowing you to tank a hit and pound back with plenty of force. Whirlwind allows you to phaze away something that's gotten one too many Quiver Dances and the like and to rack up hazard damage. Toxic is an obvious helpful move in this metagame, as steel and poison types are not very prevalent at all.
Ferroseed
Eviolite Ferroseed sports the title as the best spike layer in the metagame, only really facing competition from things like Qwilfish. Ferroseed sports excellent typing and is one of the few viable steel types in RU, which gives him plenty of uses and utility here. Ferroseed might not be able to wall as many physical threats as Tangela, but he comes damn close, being able to take on things like Durant with almost ease. Leech Seed and Spikes are a given, but the last two moveslots are up in the air for Ferroseed. He should generally use Toxic, but the last move doesn't matter much, because Ferroseed will not be inflicting any damage on opponents with Gyro Ball and the like any time soon. Ferroseed sports an obvious weakness to fire, so watch out when things like Entei come out to ruin your fun.
Blastoise
Easily the best spinner in the tier. You can go specially or physically defensive here, and both have their merits. Personally, I'm running specially defensive, but it's up to you. Most Blastoise will run Scald and Rapid Spin, and the next two slots are up in the air. Toxic is common and quite a good choice, and I use Ice Beam for the third slot to try and take on things like Honchkrow in an emergency. Obviously this Blastoise runs into trouble when grass types like Lilligant come in, so make sure you can handle those. Extremely powerful attackers and set up sweepers will be able to set up without much fear because Blastoise can't do much to them.
Claydol
Another excellent spinner, whom is especially great when paired with Honchkrow as they have fairly good synergy. Rapid Spin/Ice Beam/Earth Power/Toxic is the common set with Claydol, and he is very effective with it. Obviously, bug types have a field day against Claydol, so Yanmega and friends are excellent ways to go about breaking it. Sharpedo also slaughters Claydol with no trouble, being able to use either STAB to take it out.
Aggron
An underrated defensive Poke in this tier. With special defense investment he can wall most of the bug types present and either fire back with a super effective rock attack or do things like set up Stealth Rock, poison with Toxic, or even use the admittedly risky Metal Burst. Aggron is one of the few steel types in RU, and probably the best defensively, only facing competition with Steelix and Eviolite Ferroseed.
Umbreon
Umbreon is ONE OF the best WishPassers available in the tier, only facing competition from Clefable and the like, both of whom are outlcassed in most cases. Umbreon's typing is very bad in a tier full of bug Pokemon, but Umbreon can still wall basically any special sweeper that's not named Venomoth or Yanmega. Umbreon often can't do anything in return besides hit you with Toxic, so there's not a whole lot to worry about when Umbreon is out. Basically the gist to killing Umbreon is with a strong physical fighting or bug attack, so Primeape generally has a field day when Umbreon comes out.
Drapion
Drapion is probably the best in the tier at setting up Toxic Spikes, and he can also take on Cresselia fairly well. Other than that, though, there aren't many things it can do. Whirlwind and Toxic Spikes are nice on him, but he doesn't have many good forms of offense. Crunch and Rock Slide are my coverage moves on him, which allows him to have STAB and the ability to possibly fight back against bugs (Rock Slide does a number on Yanmega). Drapion also absorbs enemy Toxic Spikes, which is certainly never a bad thing.
Gastrodon
An absolute defensive monster. Gastrodon's typing is quite excellent for the tier, and he even sports a useful immunity to electric. The reason I believe Gastrodon is superior to Quagsire is because Gastrodon can actually take a hit without setting up, has an immunity to water, and can actually hit back for some damage, unlike Quagsire. You can max out your physical or special defenses and use a dual status set of Scald/Toxic/Recover/filler, and the filler can be anything from Earth Power to Ice Beam. Gastrodon is great with a special defensive set, being able to take on things like Venomoth. Obviously, however, Gastrodon does not want to take any grass attacks.
Quagsire
Similar to Gastrodon in its uses, except for one thing: Unaware. With Unaware, Quagsire ignores stat boosts on his opponent, thus making Quagsire a fairly good answer to some set up sweepers. Quagsire can even begin setting up defenses himself to tank hits like a champ. However, without any setting up, Quagsire is still hit very hard by most Pokemon in this tier and has trouble walling. Quagsire is also extremely susceptible to status unless you run Rest, which severely hampers his defensive capabilities.
Clefable
Clefable has the incredible ability Magic Guard, which makes her one of the better special walls and wish passers of the tier. She basically works like a Blissey but with immunity to status, which is quite delicious. Clefable can try to run strange offensive set-up sets, but often won't be able to do anything effective or noteworthy.
Moltres
Just because Moltres is on the defensive threat list doesn't mean you should completely dismiss him as an offensive threat; Moltres is simply seen more often as a defensive Pokemon in this tier. His most common set is the SubRoost set, which works very well to stall out opponents with Pressure and to take out various threats in the metagame. Moltres sports a 4x resistance to bug, making it one of the best answers to sweepers such as Yanmega and Venomoth (barring a Sleep Powder). Moltres can then fire back with a powerful Flamethrower or use Toxic and begin to deploy the SubRoost strategy to truly mess with the opponent. The biggest drawback to Moltres is her glaring 4x weakness to Stealth Rock. Therefore, it is very important to have a spinner on your team when using Moltres, otherwise you'll lose half of your health upon switching in when rocks are up. Gastrodon is a great defensive partner to Moltres, as he can either absorb or tank the water, rock, and electric attacks aimed at Moltres, while Moltres laughs at the grass attacks aimed at Gastrodon.
Golduck
Golduck sports good typing, a good movepool, and a good ability in Cloud Nine, which lets him counter all weather teams used in the tier. Water typing is always solid in any tier, and Golduck has a great movepool to abuse it. He can be a support Pokemon with Hypnosis and the like, or he can attempt a sweep with Calm Mind (Golduck is still considered defensive in my opinion, though). Whatever his moveset, he counters weather excellently; by simply coming in, all weather goes away. Golduck also even resists the water and ice moves commonly used on the rain and hail teams in this tier, which gives him an even more notable utility against countering rain. A set of Calm Mind/Scald/Ice Beam/Hidden Power Electric seems to be the most useful set to me, able to stop any weather and then set up and sweep before the weather goes back up.
Hail
I'm putting basically every ice type Pokemon into this category, because in most cases this is the only way they can be viable. It all starts with Eviolite Snover, who is extremely weak both offensively and defensively (you could also use scarf, but the damage output will be pitiful and not really worth it). From there, you will generally see a lot of entry hazards being put up, from spikes (Ferroseed, Qwilfish), to Stealth Rock (Gligar, Rhyperior), to Toxic Spikes (Drapion, Qwilfish). Finally, there will probably be a ghost (Cofagrigus, Dusknoir). That's the general set up of a Hail stall team here. The most potent threat that actually benefits from Hail is the infamous StallRein, who will annoy the crap out of you. But don't worry, it's not as hard to beat as everyone says. Simply inflict it with toxic or hit it with quick, powerful attacks so it can't put up a sub against you and you will be fine. The only real problem about Hail is those 100% accurate Blizzards. Things like Fridge Rotom are extremely powerful with Hail up and can dent big holes in your team. The best way to tank these hits is with Munchlax. With Thick Fat, he has a resistance to ice, and with his already insane special bulk, he won't be taking too much damage. While Munchlax is the best tank against Hail's powerful attacks, the best way to actually COUNTER Hail is through using one of the Cloud Nine Pokemon: Golduck, Altaria, or Lickilicky (but mostly Golduck and Lickilicky, as Altaria is weak to ice). Golduck and Lickilicky both can rid the field of Hail and give the common Hail Pokemon some serious trouble with their large movepools and utility. Rain teams can throw up their own weather to disrupt the Hail and use their insane amounts of power to punch holes in the hail team...you just have to make sure you kill that Snover.
Cofagrigus
Cofagrigus is a generic defensive ghost type with a massive defense stat. The only thing that's really special and unique about him is his ability Mummy, which more or less takes away the ability of a physical attacker. This can be extremely useful against things like Guts Hariyama or Swellow, who rely on their abilities to put together a proper sweep. Cofagrigus can Will-O-Wisp physical attackers to really screw them over for the whole match, but he doesn't have much use other than that and the obvious fact that he blocks rapid spin. A Calm Mind set is decently viable and can do some damage, just watch out for things like Honchkrow that can seriously dent you despite your high defense. The thing that really hurts Cofagrigus is his lack of recovery, so you'll have to rely on things like Rest to stay alive.
Dusknoir
Dusknoir is the other decent ghost in this tier. Dusknoir is probably better than Cofagrigus in most aspects; the only thing Cofagrigus has is his ability and thus easy means to handle Guts Swellow. Dusknoir is basically in the same boat in Cofagrigus in terms of effectiveness, though; he has no real means of recovery outside of Rest or Pain Split, so it's hard for him to wall for a long time against the heavy hitters in this metagame. Dusknoir can Will-O-Wisp physical attackers and the like just like any other ghost, really, but one of the decent draws to Dusknoir is the fact that he actually has a pretty decent attack stat and can do some damage. He can run an excellent Choice Band set (which is pretty underrated in my opinion), and he even can run some strong priority on that set. Dusknoir has the natural bulk to tank hits even without any investment and pound back with a strong Shadow Punch or Earthquake, and then come in later to kill with a priority Shadow Sneak. Dusknoir obviously has the utility of blocking rapid spin, and is a great choice if you'd like to keep your hazards on the field.
Lickilicky
Lickilicky is a fairly decent WishPasser in this tier and is a decently potent special sponge with a great amount of utility. He also sports the great ability Cloud Nine, which eliminates weather and makes Lickilicky a great answer to Hail and Rain teams. A moveset of Wish/Protect/Toxic/Dragon Tail has excellent merits on Lickilicky, allowing him to pass high HP wishes to his team and phaze around special attackers. Lickilicky is capable of taking quite a beating from things like Cresselia or Yanmega and he can status them, phaze them out, or simply recover himself so he can extensively and effectively wall them. A good thing to have with that set is hazards to take advantage of the phazing from Dragon Tail. Lickilicky faces competition as a WishPasser with things like Clefable, who has Magic Guard, and Audino who has Regenerator. All have their merits that make them useful on your team, so look into what you need as a WishPasser if you're going to use one on your team.
Articuno
The frozen legendary bird swoops into RU as one of the best special sponges in the tier, only really unfortunately held back by a glaring Stealth Rock weaknesses and a bunch of other unfortunate weakness on top of that. Articuno's incredible special defense stat lets him tank most of the common bug-type special sweepers present in the tier, and he can fire back with Toxic or a STAB Ice Beam that will do decent damage coming off of a base 95 special attack. Articuno loves to run a SubRoost set that is extremely similar to the set Moltres often runs, so they both do nearly the same things but with Articuno having better special bulk. However, Articuno's numerous painful weakness (rock, fire, electric, steel), and lack of any useful resistances outside of bug make him a generally inferior choice when compared to Moltres, who has less weaknesses (just rock, water, and electric), and more useful resistances (quad resistance to bug and grass, resistance to fighting, fire, and steel).
Slowking
Slowking is yet another potent special sponge available in this tier, but he mostly shines on Trick Room teams, where his absurdly low speed can be paired with access to Nasty Plot and a good special movepool to wreak havoc among an opponent's team. However, Slowking is still a more defensive threat in my eyes, as he's basically a specially defensive version of Slowbro, having access to the solid typing and Regenerator which allows him to come in and wall for the entire match. Slowking's physical defense is still rather horrid though, so you have to make sure you watch out for any physical attacks that might come Slowking's way.
Gligar
Gligar is one of the better Eviolite users in the tier, being a perfect counter to any fighting type or physical bug type in the tier. Gligar is one of the few viable Eviolite users with access to instant recovery in Roost, making him a perfect candidate as a physical wall. Gligar can take on the likes of Durant, Gallade, Primeape, etcetera, and come out on top every time by inflicting status, setting up Stealth Rock, or simply roosting until his health is high. The only real issue with Gligar is his inability to really do any damage back besides inflicting Toxic, because his attack stat is very low and his Earthquakes won't be doing much to anybody. Regardless, Gligar is a great Pokemon to set up Stealth Rock for your team and is good to employ if you're having trouble with some of the metagame's physical threats.
Uxie
Uxie is probably one of the best "leads" I have seen in the entire metagame. Very little things OHKO him, and the few things that do are things like Specs Yanmega Bug Buzz, Venomoth at +2, etc. Basically, killing Uxie is very hard, and he has some very good utility that makes him invaluable in this metagame. Uxie's utility ranges from setting up Stealth Rock, to tricking a scarf, to spreading status such as poison or paralysis, to even setting up any weather you want with efficiency and U-turning out to a sweeper when it's done. Uxie can even pseudo-phaze by using Yawn. Basically, there's a lot of reasons to use Uxie, but one reason NOT to use him would be because he simply can't do anything once all of those utility jobs are complete. If Uxie is your last Pokemon in a match, unless you're running Toxic, you won't be able to do anything except fire off extremely weak U-turns or Psychics or something. Generally, Uxie is as good as support gets in this tier, but that's about all it can do.
If anyone thinks of other things, let me know and I'll add them to the lists.
Offensive Threats:
Honchkrow
This guy can run Choice Band, Choice Scarf, Mixed or Physical All Out Life Orb, or Bulky Sub, and all of them are extremely strong. Even a Nasty Plot set is probably viable for shock value alone. My personal favorite is the Bulky Sub Krow, but personal preference is for a different discussion. This guy's Brave Birds are extremely strong, and you have to watch out for his Sucker Punches as well. The best stop to this is Eviolite Rhydon or Rhyperior, who laughs at the Brave Birds and doesn't care about Sucker Punch as he attempts to use Stone Edge. Superpower does decent damage as it is on a lot of Honchkrow's sets, but it's not even a 2hko on Rhyperior and DEFINITELY not on that Eviolite Rhydon. Honch usually isn't that bulky (unless its the sub set), so priority can do a number on it in the forms of Mach Punch from various mons in the meta. Honch is also quite slow so it can be revenge killed by most speedy things that aren't afraid of Sucker Punch, which makes Primeape an excellent revenge killer (but obviously you can't switch him into a Brave Bird). A good partner for Honchkrow on your own teams is definitely a rapid spinner, as Honch does not enjoy Life Orb damage + Stealth Rock damage + Brave Bird recoil, which can severely hamper his sweep. Claydol has decent synergy with Honchkrow, being immune to electric and resisting rock attacks. Claydol can also work to set up his own Stealth Rocks to hamper the opposing team.
The Quiver Dancers - Venomoth, Lilligant
These are the two most viable Quiver Dancers in the tier, but really anything with Quiver Dance can cause havoc (lol Butterfree). Both of these function mostly in the same way and both have merits to being used over the other. Regardless, Quiver Dance boosts speed, special attack, and special defense, and after one or two of these you really can't expect to be killing them with a special move. Furthermore, both of these Pokemon commonly run Sleep Powder to eliminate their counters (which there are not very many of). Venomoth has Tinted Lens which ignores resistances and makes its Bug Buzzes absurdly hard to stop, and Lilligant has Own Tempo Petal Dance or Giga Drain for either massive damage or recovery to help increase the longevity of their sweeps. They are both perfectly capable of running bulky RestTalk sets and all-out offensive sweeping sets, and both are extremely powerful in this metagame. The best way to stop the sweeping sets is to inflict them with a status (paralyze or burn, since Venomoth can't be toxiced) or hit them with a speedy scarf user before they accumulate multiple Quiver Dances. Scarf Typhlosion outspeeds Venomoth after +1, but I don't think he outspeeds max speed Lilligant (correct me if I'm wrong. Either way, Lilligant usually won't do too much to Typhlosion). Typhlosion can then attack with a strong super effective fire attack and decimate the dancers. The Rest Talking sets are much more difficult to stop, and you have to be on top of your game against them and knock them out before they start getting too powerful. You can weaken them so they use Rest and hope the Sleep Talk doesn't hit their attacking move while you try to pummel them with a Brave Bird or something, but that can be very risky at times. Basically you just can't let the RestTalking sets get set up. In the realm of walling these Pokemon, Eviolite Munchlax is a pretty sure bet, and he can phaze both out with Whirlwind. You only have to be wary of Sleep Powder. Moltres can sometimes wall them depending on the set, but if people catch on to my Lilligant set that uses HP Rock, Moltres will definitely not be walling anytime soon. Venomoth likes a Rapid Spinning partner since she has a Stealth Rock weakness, and Lilligant appreciates a lack of Toxic Spikes on the field since she is very susceptible to those.
Yanmega
Pretty much the biggest menace in the entire tier. He is capable of running two extremely powerful sets: a speed booster, and a SpecsLens set. Both sets are incredibly powerful, and if you don't have the right check/counter on your team, you WILL get swept. The Speed Boost set uses Protect to get a boost and then will be outspeeded by basically nothing, and Yanmega will be free to fire off Bug Buzzes and Air Slashes (and then a third move which is up in the air. Giga Drain is the best option, imo). Yanmega has a high special attack stat, so it's very hard to wall this guy. The SpecsLens set is, imo, more devastating. With Tinted Lens, nothing resists Yanmega's Bug Buzz, so it's nearly impossible to take. The best counter to both sets is Eviolite Munchlax, who can fire back a Rock Slide or simply phaze Yanmega out. Rotom-S is a good stopper of the Speed Boost set, but can't take the SpecsLens's Bug Buzzes. Electrode is immune to Bug Buzz, resists Air Slash, and fire back with super effective electric attacks, but can't take HP Ground if that's Yanmega's third coverage move. Specially Defensive Gastrodon can tank a few hits as long as Yanmega isn't running Giga Drain, but is not going to enjoy Specs boosted Bug Buzzes. Basically, the Speed Boost set has a few decent checks, but there really isn't any counter to the SpecsLens set. In terms of teammates for Yanmega, once again a spinner is appreciated, but most people run Yanmega in the lead position so the 4x Stealth Rocks weakness can't be exploited.
Sharpedo
Sharpedo is another Speed Booster that wreaks havoc in this tier, and is even more dangerous in the rain. The most threatening set is his Mixed set, with Surf/Crunch/Ice Beam/Protect, of which there aren't a ton of counters too. The best answer is Eviolite Ferroseed, who walls basically any Sharpedo set to death. Tangela doesn't have a problem either if Sharpedo doesn't have Ice Beam, but it often does have Ice Beam which poses a problem. Blastoise is a great tanking check, and can even burn Sharpedo with Scald to severely hamper its efficiency. Gastrodon is another excellent answer, as he is immune to water attacks and is bulky enough to take the other attacks Sharpedo can throw at him. Sharpedo is also weak to fighting priority, which makes Hitmonchan or anything else with Mach Punch a pretty good answer.
Durant
The best way to stop Durant is to just hit it with basically anything. Seriously, it is that frail. However, if you're facing a good Durant player that eliminates your priority users and scarf mons, you're in for some hurt, because Hone Claws Hustle Durant will slaughter basically anything in the tier. Iron Head/X Scissor/Stone Edge are its usual coverage moves, and are more than enough to decimate almost anything in sight. Eviolite Gligar is a great answer, as he can tank a hit and Roost of the damage with no problem, but he can't do a whole lot back, and if Durant tries to set up another Hone Claw or two, Gligar will be in serious trouble. Most Scarf Pokemon, like Scarf Typhlosion, will have no trouble KO'ing Durant, as Durant is incredibly frail.
Rhydon/Rhyperior
Rhydon and Rhyperior are serious heavy hitters in this tier. Earthquake and Stone Edge are the only coverage moves they really need to achieve excellent coverage. The common sets are Rock Polish, SubSD, or a simple tank that sets up Stealth Rock and Phazes (some sets might even try to use both Rock Polish AND Swords Dance. If that player manages to set this up on you...good luck. You'll need it). Every set Rhyperior uses is walled by Eviolite Ferroseed, Tangela, and Gligar (if you haven't noticed, it's good to run one of these three on your team). One of the best ways to take care of any Rhyperior set that's not the Rock Polish set is by simply using something faster than it (which is basically everything) that can exploit one of Rhyperior's 4x weaknesses (water and grass). Blastoise is a great tanking answer, while Sharpedo basically uses Rhyperior as set up fodder. The differences between Rhydon and Rhyperior are simply a matter of more defenses versus leftovers recovery. It's really the same issue as Blissey versus Eviolite Chansey. Players that plan on using one of these Pokemon as a utility Pokemon or a Rock Polisher should use Rhyperior, but the SubSD is probably more potent on Rhydon as he can tank almost any physical attack in existence, and most won't even break his sub.
Galvantula
Another bug type! (Noticing a pattern?) Galvantula's best set is his Choice Specs set, where he uses Compound Eyes to boost his accuracy so he can fire off Thunders all over the place. Some players use Expert Belt to give the allusion that he's holding Specs to take a player by surprise, so take that into account. Usually the coverage moves used are Thunder/Bug Buzz/Energy Ball/HP Fire, and these moves provide excellent coverage in this metagame. Once again, Munchlax is the premier special wall in the tier and can tank Galvantula's hits fairly well. If our electric spider is choiced, you can switch around to take resisted or immune hits, such as switching in Rhyperior on a Thunder. If you're putting Galvantula on your team, you want a spinner so you can keep bringing in your spider to fire off those Thunders since Galvantula is susceptible to every type of entry hazard.
Alakazam
A menace of destruction that almost no one uses (I used him to get up to top 20 on the ladder). The best set, in my opinion, is SubCm with Psychock and Focus Blast. With this, Alakazam can use his insane speed to set up a quick Sub and get fast Calm Minds in until he isn't even touched by Special Attackers. Psyshock is used over Psychic to make this a Cresselia killer; most Cresselia like to try and set up Calm Minds alongside you, thinking it's going to be a stalemate in the end. But then you surprise them by hitting them for over 50% with a +6 Psychock. Still, considering how common bug types are in this tier, Alakazam gets faced with some tough situations quite often. Things with strong priority like Choice Band Entei can knock Alakazam out of commission. Frankly, physical attackers that are faster than Alakazam in general are a bit of a problem. Yanmega hurts Alakazam bad after it gets some Speed Boosts and the ability to outspeed Zam.
Rain
This is very general, because there are multiple viable rain sweepers. Rain as a whole is very powerful and arguably broken in this tier. You will often see Electrode setting up an 8-turn monsoon of destruction where Shell Smash Omastars, Ludicolos, and Swords Dancing Kabutopses rip our face in half. There aren't many good answers to this besides trying to stall out the rain. Rain Dish Blastoise does well against everything but Ludicolo. Running a Rain Dish Ludicolo on your own team can help wall the sweepers. Pokemon with the Cloud Nine ability can help by getting rid of the rain (so Golduck and Lickilicky I think...nothing else <_<). Eviolite Ferroseed and Tangela wall the offensive rain sweepers but are in serious trouble if they face anything special. If you survive the initial rain onslaught, try to KO the Pokemon that set the rain up before they can get it off so you don't have to feel the pain again. Another decent answer to rain is Sharpedo, who can use your opponent's rain to fire off boosted Surfs, and can let Speed Boost accumulate until he's faster than the rain sweepers (Yanmega is in the same boat here to an extent, and can use Giga Drain and Bug Buzz to kill off Omastar, Kabutops, and Ludicolo).
Entei
Entei is capable of running excellent sets in both the physical and special categories, make him very unpredictable and very hard to wall. His Choice Band set is very powerful, and you'll often get hit with STAB Flare Blitzes and priority in the form of Extremespeed. It's hard to take these hits, and your best bets are Eviolite Gligar, Cresselia, or Gastrodon. The Calm Mind set is harder to wall, and can run either Sub or RestTalk to eliminate the possibility of status and eventual damage. Munchlax doesn't have much of a problem taking Entei's hits and can whirlwind him out. Cresselia can Calm Mind alongside Entei and the CM battle will end in a stalemate. Gastrodon will win against any Entei set almost every time unless Entei is using something bizarre like HP Grass.
Porygon-Z
One should always make sure they're capable of taking on Porygon-Z...otherwise, you're in for a miserable time of getting slaughtered by Adaptability or Download boosted special attacks. Porygon-Z is almost always holding a scarf or specs, but don't completely dismiss the possibility of a Nasty Plot set, because that as completely viable as well. Porygon-Z is basically the most powerful special attacker in the tier, but he is also quite frail, so he takes on the "glass cannon" persona. Having a priority user such as Hitmonchan to kill Porygon-Z is probably the most reliable way of getting rid of it, but you'll have to revenge kill because Hitmonchan is never going to come in on a specs or scarf Tri-Attack and live. Munchlax doesn't take a whole lot from P-Z's attacks, but he doesn't have any recovery so he can't exactly come in all the time. Specially Defensive Aggron has a 4x resistance to Tri-Attack and only has to worry about whatever Hidden Power Porygon is running.
Swellow
Swellow is extremely dangerous in this tier, as he can get through some of the commonly used physical walls such as Tangela or Blastoise. With Guts, STAB Brave Bird, and a very nice speed stat for RU, Swellow can wreak a lot of havoc here, dealing colossal damage to basically anything that's not Rhyperior. The good news is that Swellow's sweep will be very short; between Stealth Rock and the toxic or burn put onto itself for guts, Swellow should die pretty quick, but that's not before is murders half your team. As said before, Rhyperior chuckles as Swellow tries to break through with a resisted Brave Bird and can OHKO back with Stone Edge. Priority users can pound on Swellow's weak defenses in hopes of making it die quicker. Aggron laughs at anything Swellow can ever hope to throw at it and can throw STAB Stone Edges back at it. Cofagrigus can switch in and tank a Brave Bird and give Swellow Mummy, which takes away her Guts boost and makes her significantly less effective.
Primeape
Primeape has the honor of being probably one of the most viable fighting types in a tier that has a LOT of decent fighting types. Primeape sports a decent 95 base speed, 105 attack, and a great ability in Vital Spirit that prevents him from going to sleep. All of this works together to make Primeape a fairly potent answer to things like Venomoth when holding a scarf, because Primeape outspeeds Venomoth at +1, is immune to the sleep, and resists Bug Buzz. Primeape can then hit Venomoth with a super effective Stone Edge or Fire Punch for big damage and a KO. Outside of being a revenge killer and sleep absorber, Primeape doesn't have a whole lot of utility in this metagame though. He will never be able to touch Tangela, and other common walls such as Cofagrigus and Cresselia laugh at everything Primeape tries to throw at him (besides U-turn on Cresselia). A set of Close Combat/U-turn/Stone Edge/Ice Punch has worked fairly well for me, and has its merits as a revenge killer in this tier.
SmashPass
SmashPass is a horribly strong strategy that was even nominated for banning in OU, which probably gives you an idea of how powerful it can be in RU. While there aren't as many solid support Pokemon to help the strategy (damn Espeon), it can still be very viable and very destructive in the right hands. There are a couple worthy users of Shell Smash and Baton Pass, but the Pokemon you'll see doing it most often is Gorebyss. Gorebyss has very mediocre stats, but if you allow it to get off a Shell Smash and you don't have strong enough priority to kill it, you're likely in for some hurt, as it's probably going to pass to something insanely powerful such as Rhyperior, and once that happens...there really isn't much hope for you. The best answer to SmashPass is to stop the pass before it happens. When Gorebyss comes in, hit it as hard as you can, as its defenses aren't great and you can hopefully KO it before the destruction begins. Phazing is also a solid option as long your opponent hasn't used something like Ingrain Smeargle. If the pass does get off to something like Rhyperior, you'd better pray you can burn it or something, otherwise it's game over.
Typhlosion
Typhlosion sits here as one of the best revenge killers in the tier and sports some of the most absurdly powerful attacks imaginable with a Specs set. Really, the most viable sets are Scarf and Specs, but a SubPetaya set could be possible and extremely destructive in the right hands. Regardless, you'll most often see a Scarf set with something like Fire Blast/Eruption/Hidden Power ?/Focus Blast, and that set grants him some great coverage in this metagame. Personally, I'd say Hidden Power Grass is the best choice, so you can revenge kill any Rhyperior, even if it's a Rock Polisher at +2. Eruption at full health is Typhlosion's most powerful attack, and is easily capable of OHKO'ing things like Venomoth with a Quiver Dance under its belt. Typhlosion's great speed lets it outspeed many threats in the metagame even with boosts to their speed, even things like Yanmega with a boost. Typhlosion's specs set takes away this revenge killing ability for the most part in exchange for an insane amount of firepower. Specs+Eruption at full health = incredible damage, even against things like Thick Fat Munchlax.
Gallade
Gallade is a fairly capable physical sweeper in RU, capable of boosting his attack (and defense if using Bulk Up), and sweep with good coverage and a heck of a lot of power. Gallade's most dangerous set would be a set decently similar to Conkeldurr's popular set in OU, where you'll see Bulk Up, Drain Punch, priority (Shadow Sneak in Gallade's case), and then a coverage move, which would probably be Psycho Cut for Gallade, giving him an extra STAB and helps out the already perfect coverage on the set between Drain Punch and Shadow Sneak. Gallade is quite powerful with this set, however he isn't too fast, and can run into trouble when quick, powerful revenge killers come to take him out. Gallade's excellent special defense could potentially let him live against things like a Specs Galvantula's Bug Buzz, but he's going to have trouble against something like a Swellow's Brave Bird even with a Bulk Up or two, so the best way to take out Gallade is with his decent frailty and a strong super effective attack.
Sceptile
Swords Dance and Unburden. I'll admit I didn't come up with the idea, I only tried it out because reachzero mentioned it a few times, but my God, it is powerful. Sceptile is capable of running either physical or special set and he does both extremely well, and has enough speed to outspeed a TON of things in this metagame. You can go Specs, SubSeed, Scarf, whatever, but the most potent sweeping set is definitely SD Unburden. The set in particular I've been using is Swords Dance/Leaf Blade/Acrobat/Earthquake, with a Flight Gem equipped. Set up a Swords Dance, throw out an extremely powerful Acrobat, and then you have very high attack and a speed stat that's over 700, so you won't be outsped by anything in the tier unless it has +3 or 4 in speed (suck on some of that, Yanmega!). From there, it's an easy road to a sweep, because you'll be absolutely unstoppable, because really nothing can stop this Sceptile once it has set up properly. Something like max defense Steelix can tank a hit and phaze out Sceptile. Pokemon with strong priority can pound Sceptile's lackluster defenses in hopes of KO'ing it before Sceptile unleashes it's wrath.
Manectric
Manectric is a fairly good user of Scarf/Specs and competes for a spot with Galvantula in most cases. The advantage Manectric has are Switcheroo, which is basically like Trick and can effectively screw over almost any wall, and the ability to use fire attacks such as Overheat. However, Galvantula can use bug attacks and has Compoundeyes so he can run more powerful moves like Thunder. Either way, both are capable of punching holes in your team, and it just depends on what you're looking for in an electric type special attacker.
Defensive Threats:
Cresselia
The queen of this tier (the king is Yanmega. They're a cute couple). Anyway, Cresselia is insanely good in this tier. Her defenses are through the roof, and her common sets are Rest or Sub with Calm Mind, and a simple support set. On her calm mind sets, the best way to take her out is with a very strong, super effective physical attack, because once she starts setting up, your special attacks will not be touching her at all. Status doesn't work since the common sets are Sub and RestTalk. A good Cress player won't attempt a final sweep until it's their final Pokemon, so basically you just have to try and hit it as hard as you can or you're absolutely screwed. A strong pursuit user like Honchkrow can smack it around a bit. Fellow calm mind users can set up alongside Cress and initiate a stalemate. CM Alakazam with Psychock is an excellent Cress killer because Psychock will do hefty damage with +6 special attack while Cress won't be able to touch you. If you're putting Cresselia on your team, you really don't need any support for her at all, as she can sweep on her own incredibly well. Just try to knock all bug types out of commission before attempting your sweep.
Tangela
Eviolite Tangela is probably the best physical wall in existence. Sporting a defense over 500 and an HP stat in the mid 300's, Tangela laughs at any physical attack you can muster, even tanking a Flare Blitz from Entei and striking back with something like Leech Seed or Sleep Powder. Tangela also has Regenerate, which actually allows him to recover some of his HP, unlike other Eviolite users. Tangela's best set by far is Leech Seed/Sleep Powder/Knock Off/Giga Drain. With that set, you can completely screw with any physical attacker by Knocking Off their Life Orbs, putting them to sleep, or leech seeding them for recovery. Knock Off also completely ruins fellow Eviolite users or things that rely on Leftovers to survive for a long time, making it an excellent move to put on Tangela. Sleep Powder is an obvious useful move on any team, and Giga Drain is Tangela's most preferred move for attacking, as it gives him recovery and a decent way to put a dent in powerful attackers such as Rhyperior. Unfortunately, Tangela can not take any special attacks at all, and will fall quickly to Flamethrowers and Bug Buzzes, making it essential to have some sort of specially defensive threat on your team as well.
Munchlax
Eviolite Munchlax is a specially defensive monster. He is one of the best answers to Yanmega, Moltres, Omastar...the list goes on. With an Eviolite, Munchlax sports something like 440/440 special defenses, so he is nearly untouched by most special attacks. With Frustration/Rock Slide/Toxic/Whirlwind, you have plenty of options against opponents like Yanmega. Rock Slide does something like 80% to most Yanmegas, while Bug Buzz will do very little to Munchlax here, allowing you to tank a hit and pound back with plenty of force. Whirlwind allows you to phaze away something that's gotten one too many Quiver Dances and the like and to rack up hazard damage. Toxic is an obvious helpful move in this metagame, as steel and poison types are not very prevalent at all.
Ferroseed
Eviolite Ferroseed sports the title as the best spike layer in the metagame, only really facing competition from things like Qwilfish. Ferroseed sports excellent typing and is one of the few viable steel types in RU, which gives him plenty of uses and utility here. Ferroseed might not be able to wall as many physical threats as Tangela, but he comes damn close, being able to take on things like Durant with almost ease. Leech Seed and Spikes are a given, but the last two moveslots are up in the air for Ferroseed. He should generally use Toxic, but the last move doesn't matter much, because Ferroseed will not be inflicting any damage on opponents with Gyro Ball and the like any time soon. Ferroseed sports an obvious weakness to fire, so watch out when things like Entei come out to ruin your fun.
Blastoise
Easily the best spinner in the tier. You can go specially or physically defensive here, and both have their merits. Personally, I'm running specially defensive, but it's up to you. Most Blastoise will run Scald and Rapid Spin, and the next two slots are up in the air. Toxic is common and quite a good choice, and I use Ice Beam for the third slot to try and take on things like Honchkrow in an emergency. Obviously this Blastoise runs into trouble when grass types like Lilligant come in, so make sure you can handle those. Extremely powerful attackers and set up sweepers will be able to set up without much fear because Blastoise can't do much to them.
Claydol
Another excellent spinner, whom is especially great when paired with Honchkrow as they have fairly good synergy. Rapid Spin/Ice Beam/Earth Power/Toxic is the common set with Claydol, and he is very effective with it. Obviously, bug types have a field day against Claydol, so Yanmega and friends are excellent ways to go about breaking it. Sharpedo also slaughters Claydol with no trouble, being able to use either STAB to take it out.
Aggron
An underrated defensive Poke in this tier. With special defense investment he can wall most of the bug types present and either fire back with a super effective rock attack or do things like set up Stealth Rock, poison with Toxic, or even use the admittedly risky Metal Burst. Aggron is one of the few steel types in RU, and probably the best defensively, only facing competition with Steelix and Eviolite Ferroseed.
Umbreon
Umbreon is ONE OF the best WishPassers available in the tier, only facing competition from Clefable and the like, both of whom are outlcassed in most cases. Umbreon's typing is very bad in a tier full of bug Pokemon, but Umbreon can still wall basically any special sweeper that's not named Venomoth or Yanmega. Umbreon often can't do anything in return besides hit you with Toxic, so there's not a whole lot to worry about when Umbreon is out. Basically the gist to killing Umbreon is with a strong physical fighting or bug attack, so Primeape generally has a field day when Umbreon comes out.
Drapion
Drapion is probably the best in the tier at setting up Toxic Spikes, and he can also take on Cresselia fairly well. Other than that, though, there aren't many things it can do. Whirlwind and Toxic Spikes are nice on him, but he doesn't have many good forms of offense. Crunch and Rock Slide are my coverage moves on him, which allows him to have STAB and the ability to possibly fight back against bugs (Rock Slide does a number on Yanmega). Drapion also absorbs enemy Toxic Spikes, which is certainly never a bad thing.
Gastrodon
An absolute defensive monster. Gastrodon's typing is quite excellent for the tier, and he even sports a useful immunity to electric. The reason I believe Gastrodon is superior to Quagsire is because Gastrodon can actually take a hit without setting up, has an immunity to water, and can actually hit back for some damage, unlike Quagsire. You can max out your physical or special defenses and use a dual status set of Scald/Toxic/Recover/filler, and the filler can be anything from Earth Power to Ice Beam. Gastrodon is great with a special defensive set, being able to take on things like Venomoth. Obviously, however, Gastrodon does not want to take any grass attacks.
Quagsire
Similar to Gastrodon in its uses, except for one thing: Unaware. With Unaware, Quagsire ignores stat boosts on his opponent, thus making Quagsire a fairly good answer to some set up sweepers. Quagsire can even begin setting up defenses himself to tank hits like a champ. However, without any setting up, Quagsire is still hit very hard by most Pokemon in this tier and has trouble walling. Quagsire is also extremely susceptible to status unless you run Rest, which severely hampers his defensive capabilities.
Clefable
Clefable has the incredible ability Magic Guard, which makes her one of the better special walls and wish passers of the tier. She basically works like a Blissey but with immunity to status, which is quite delicious. Clefable can try to run strange offensive set-up sets, but often won't be able to do anything effective or noteworthy.
Moltres
Just because Moltres is on the defensive threat list doesn't mean you should completely dismiss him as an offensive threat; Moltres is simply seen more often as a defensive Pokemon in this tier. His most common set is the SubRoost set, which works very well to stall out opponents with Pressure and to take out various threats in the metagame. Moltres sports a 4x resistance to bug, making it one of the best answers to sweepers such as Yanmega and Venomoth (barring a Sleep Powder). Moltres can then fire back with a powerful Flamethrower or use Toxic and begin to deploy the SubRoost strategy to truly mess with the opponent. The biggest drawback to Moltres is her glaring 4x weakness to Stealth Rock. Therefore, it is very important to have a spinner on your team when using Moltres, otherwise you'll lose half of your health upon switching in when rocks are up. Gastrodon is a great defensive partner to Moltres, as he can either absorb or tank the water, rock, and electric attacks aimed at Moltres, while Moltres laughs at the grass attacks aimed at Gastrodon.
Golduck
Golduck sports good typing, a good movepool, and a good ability in Cloud Nine, which lets him counter all weather teams used in the tier. Water typing is always solid in any tier, and Golduck has a great movepool to abuse it. He can be a support Pokemon with Hypnosis and the like, or he can attempt a sweep with Calm Mind (Golduck is still considered defensive in my opinion, though). Whatever his moveset, he counters weather excellently; by simply coming in, all weather goes away. Golduck also even resists the water and ice moves commonly used on the rain and hail teams in this tier, which gives him an even more notable utility against countering rain. A set of Calm Mind/Scald/Ice Beam/Hidden Power Electric seems to be the most useful set to me, able to stop any weather and then set up and sweep before the weather goes back up.
Hail
I'm putting basically every ice type Pokemon into this category, because in most cases this is the only way they can be viable. It all starts with Eviolite Snover, who is extremely weak both offensively and defensively (you could also use scarf, but the damage output will be pitiful and not really worth it). From there, you will generally see a lot of entry hazards being put up, from spikes (Ferroseed, Qwilfish), to Stealth Rock (Gligar, Rhyperior), to Toxic Spikes (Drapion, Qwilfish). Finally, there will probably be a ghost (Cofagrigus, Dusknoir). That's the general set up of a Hail stall team here. The most potent threat that actually benefits from Hail is the infamous StallRein, who will annoy the crap out of you. But don't worry, it's not as hard to beat as everyone says. Simply inflict it with toxic or hit it with quick, powerful attacks so it can't put up a sub against you and you will be fine. The only real problem about Hail is those 100% accurate Blizzards. Things like Fridge Rotom are extremely powerful with Hail up and can dent big holes in your team. The best way to tank these hits is with Munchlax. With Thick Fat, he has a resistance to ice, and with his already insane special bulk, he won't be taking too much damage. While Munchlax is the best tank against Hail's powerful attacks, the best way to actually COUNTER Hail is through using one of the Cloud Nine Pokemon: Golduck, Altaria, or Lickilicky (but mostly Golduck and Lickilicky, as Altaria is weak to ice). Golduck and Lickilicky both can rid the field of Hail and give the common Hail Pokemon some serious trouble with their large movepools and utility. Rain teams can throw up their own weather to disrupt the Hail and use their insane amounts of power to punch holes in the hail team...you just have to make sure you kill that Snover.
Cofagrigus
Cofagrigus is a generic defensive ghost type with a massive defense stat. The only thing that's really special and unique about him is his ability Mummy, which more or less takes away the ability of a physical attacker. This can be extremely useful against things like Guts Hariyama or Swellow, who rely on their abilities to put together a proper sweep. Cofagrigus can Will-O-Wisp physical attackers to really screw them over for the whole match, but he doesn't have much use other than that and the obvious fact that he blocks rapid spin. A Calm Mind set is decently viable and can do some damage, just watch out for things like Honchkrow that can seriously dent you despite your high defense. The thing that really hurts Cofagrigus is his lack of recovery, so you'll have to rely on things like Rest to stay alive.
Dusknoir
Dusknoir is the other decent ghost in this tier. Dusknoir is probably better than Cofagrigus in most aspects; the only thing Cofagrigus has is his ability and thus easy means to handle Guts Swellow. Dusknoir is basically in the same boat in Cofagrigus in terms of effectiveness, though; he has no real means of recovery outside of Rest or Pain Split, so it's hard for him to wall for a long time against the heavy hitters in this metagame. Dusknoir can Will-O-Wisp physical attackers and the like just like any other ghost, really, but one of the decent draws to Dusknoir is the fact that he actually has a pretty decent attack stat and can do some damage. He can run an excellent Choice Band set (which is pretty underrated in my opinion), and he even can run some strong priority on that set. Dusknoir has the natural bulk to tank hits even without any investment and pound back with a strong Shadow Punch or Earthquake, and then come in later to kill with a priority Shadow Sneak. Dusknoir obviously has the utility of blocking rapid spin, and is a great choice if you'd like to keep your hazards on the field.
Lickilicky
Lickilicky is a fairly decent WishPasser in this tier and is a decently potent special sponge with a great amount of utility. He also sports the great ability Cloud Nine, which eliminates weather and makes Lickilicky a great answer to Hail and Rain teams. A moveset of Wish/Protect/Toxic/Dragon Tail has excellent merits on Lickilicky, allowing him to pass high HP wishes to his team and phaze around special attackers. Lickilicky is capable of taking quite a beating from things like Cresselia or Yanmega and he can status them, phaze them out, or simply recover himself so he can extensively and effectively wall them. A good thing to have with that set is hazards to take advantage of the phazing from Dragon Tail. Lickilicky faces competition as a WishPasser with things like Clefable, who has Magic Guard, and Audino who has Regenerator. All have their merits that make them useful on your team, so look into what you need as a WishPasser if you're going to use one on your team.
Articuno
The frozen legendary bird swoops into RU as one of the best special sponges in the tier, only really unfortunately held back by a glaring Stealth Rock weaknesses and a bunch of other unfortunate weakness on top of that. Articuno's incredible special defense stat lets him tank most of the common bug-type special sweepers present in the tier, and he can fire back with Toxic or a STAB Ice Beam that will do decent damage coming off of a base 95 special attack. Articuno loves to run a SubRoost set that is extremely similar to the set Moltres often runs, so they both do nearly the same things but with Articuno having better special bulk. However, Articuno's numerous painful weakness (rock, fire, electric, steel), and lack of any useful resistances outside of bug make him a generally inferior choice when compared to Moltres, who has less weaknesses (just rock, water, and electric), and more useful resistances (quad resistance to bug and grass, resistance to fighting, fire, and steel).
Slowking
Slowking is yet another potent special sponge available in this tier, but he mostly shines on Trick Room teams, where his absurdly low speed can be paired with access to Nasty Plot and a good special movepool to wreak havoc among an opponent's team. However, Slowking is still a more defensive threat in my eyes, as he's basically a specially defensive version of Slowbro, having access to the solid typing and Regenerator which allows him to come in and wall for the entire match. Slowking's physical defense is still rather horrid though, so you have to make sure you watch out for any physical attacks that might come Slowking's way.
Gligar
Gligar is one of the better Eviolite users in the tier, being a perfect counter to any fighting type or physical bug type in the tier. Gligar is one of the few viable Eviolite users with access to instant recovery in Roost, making him a perfect candidate as a physical wall. Gligar can take on the likes of Durant, Gallade, Primeape, etcetera, and come out on top every time by inflicting status, setting up Stealth Rock, or simply roosting until his health is high. The only real issue with Gligar is his inability to really do any damage back besides inflicting Toxic, because his attack stat is very low and his Earthquakes won't be doing much to anybody. Regardless, Gligar is a great Pokemon to set up Stealth Rock for your team and is good to employ if you're having trouble with some of the metagame's physical threats.
Uxie
Uxie is probably one of the best "leads" I have seen in the entire metagame. Very little things OHKO him, and the few things that do are things like Specs Yanmega Bug Buzz, Venomoth at +2, etc. Basically, killing Uxie is very hard, and he has some very good utility that makes him invaluable in this metagame. Uxie's utility ranges from setting up Stealth Rock, to tricking a scarf, to spreading status such as poison or paralysis, to even setting up any weather you want with efficiency and U-turning out to a sweeper when it's done. Uxie can even pseudo-phaze by using Yawn. Basically, there's a lot of reasons to use Uxie, but one reason NOT to use him would be because he simply can't do anything once all of those utility jobs are complete. If Uxie is your last Pokemon in a match, unless you're running Toxic, you won't be able to do anything except fire off extremely weak U-turns or Psychics or something. Generally, Uxie is as good as support gets in this tier, but that's about all it can do.
