A+
Celebi: Celebi is an incredible Pokemon in the current meta. It's sole existence can literally change the entire purpose of a specific Pokemon (the rise of Ebelt HP Bug Keldeo) Celebi is pretty much the best Pokemon in the game against Rain and Sand teams especially with Baton Pass. With the current metagame being filled to the brim with Rain/Sand, I would (personally) call it the best A-Rank Pokemon. Its weakness to sun is not too big of a problem when it partners amazingly with Heatran; arguably the best Sun Check in the game.
Garchomp: Garchomp is a beast. It has been nominated here to S-Rank a few times before. SubSD YacheChomp can possibly be the most threatening wallbreaker that ever existed (Hi Hydreigon) and the SubSalac Chomp set that is starting to rise is really good as well. It can also run Choice sets very effectively, with CB Garchomp hitting really damn hard. The funniest part about this entire thing is that I haven't even spoken about the Stealth Rock sets, which shows how diverse of an offensive threat this thing can be. It also works well with most weather teams, using Aqua Tail Garchomp in the Rain (cuz screw Lando-T) as well as having great synergy with the main weather sweepers (Garchomp works with Stoutland well, especially with Fblast Lure. I've seen a few Rain teams with Chomp in it, as well as Sun). Garchomp is pretty much the ideal goodstuffs mon. Deservant of A+
Hippowdon: Probably the first thing that's gonna be disagreed with. Hippowdon is a really good Pokemon. It functions as a solid physical wall while being a massive asset in Sand Stall teams -- a rather commonly seen playstyle in tournaments. Hippowdon can also function as either an incredible mixed wall, or a sole physical wall to pretty much stop guys like Terrakion right in there tracks. It is also imo the most reliable SR setter for stall teams in the entire game. Hippowdon is also the only weather inducer that has recovery (Abomasnow has Leech Seed, TUO is a filthy liar) which gives it a massive advantage in the weather war -- which is really important in BW2.
Jirachi: You probably got blown up by SubCM Jirachi one time in your life. You probably also got super pissed off at ParaFlinch Rachi. You also probably got surprise-revenge killed by a Scarf Jirachi. That's just the start. Jirachi is so versatile but it doesn't suffer the "jack of all trades; master of none" syndrome as it can run pretty much every set it uses to its fullest effect and can each of them really well. It can also pretty much fit into every playstyle. It is a great revenge killer on Hyper Offense teams, a good momentum setter/Lati@s check for sun (yeah I'm kinda pushing it) it can function like a beast in Rain, and works rather well on Sand Stall/Balanced teams. Jirachi is an incredibly good Pokemon all around.
Latios: Ironic that the Pokemon I'm talking about next is walled by the Pokemon above it. Well, Latios is a huge offensive threat. I just wanna make this quick because there really isn't much to say. Offensive check to Keldeo/Landorus/Breloom. Nearly nothing switches in. Trick cripples walls. Amazing bluffing capabilities with Expert Belt sets. Craps on Sun. Fastest Scarfer in the meta. Pretty much all you have to say about Latios. Dealing with KelTarBreloom while maintaining the most offensive momentum is quite the feat.
Thundurus-Therian: Alright remember what I said about Celebi? Well this thing is the 2nd best A-Rank mon. While Celebi is that good because of how anti-meta it is, Thundy-T is good because it's just overall good. Thundy-T can smash Rain really well while not really hampered by anything in the meta that weakens its effectiveness (like how Rain affects Nape, Kyurem-B with Fighting-Types etc.) as it can resolve any of those possible issues either with an Agility boost or a Nasty Plot boost. Thundurus-Therian can run 5 sets effectively: Nasty Plot dedicated Wallbreaker, Agility wrecks offense if it gets 1 boost, Double Dance is probably the best set, combining both above, Choice Scarf and Ebelt. Thundurus-Therian has a weird sense of versatility among those sets, even though it is just a mix and match of a few moves. It also brings a few resistances and immunities to the table which is always nice.
Tyranitar: Tyranitar is the key to letting the beasts roam wild (Keldeo and Landorus) Tyranitar fills a role that is probably the best thing to have in this meta -- a bulky but Powerful Pursuit user. Pursuit is so damn good in this meta with Psychic and Ghost-types being the main force that is used against the top ranked Pokemon in the current metagame. To add to that more, it has access to infinite sandstorm which is amazing with dealing with opposing weathers. That's not even the end of it. It can function as an exceptional lure with either mixed sets, or just 2HKOing the Skarmory with a CB Stone Edge after SR. There are a lot of interesting sets that are being discovered for this guy which makes him unpredictable while giving massive offensive utility to a team. Lastly, it can also be good on stall teams that suffer against Latios (think Amoongbro) as well as being really bulky with the Specially Defensive set.
A
Dragonite: Dragonite is a shadow of what is used to be in BW1. It's still effective, but a lot less then it used to be. Dragonite has 2 good sets atm: CB and DD. I have to say CBNite is absolutely brilliant. It's really bulky thanks to multiscale and it's good resistances and smashes every single switch-in with proper prediction. The other set is Dragon Dance, which is still a good mid-game sweeper hole puncher that can do really well opening some guys up thanks to it having good ways to setup. The meta is still rather unkind to it with checks to Dnite going left and right. However, Dragonite is just so good overall that it can maintain its place as a staple in OU. Actually, the reason I'm keeping this in A rather than A- is just because it has the rare ability to check Sun.
Ferrothorn: Ferrothorn is a very good wall. It has access to the coveted SR+Spikes combo while still having access to good support moves that stop it from being setup bait such as Twave and Gyro Ball. It also has good longevity in the form of Leech Seed. Ferrothorn pretty much has all the stuff to be a good wall. A Water resist, a dragon resist, and amazing typing which is complimented by the best playstyle out there. However, the fact that the main offensive S-Rank threats can beat it out as well as the idea that Ferrothorn is a rare sight outside of rain in high levels of play limits Ferrothorn to A.
Heatran: Heatran is a Pokemon that loses to all the S-Rank Pokemon, loses to every rain Pokemon, every Fighting Pokemon and is possible to trap but this thing is still all the way up here. This is due to the fact that Heatran deals with nearly everything else. I have a lot of trouble not fitting him into my team unless it's really dumb to do so because he brings a lot of offensive utility to the plate. It offensively checks sun which is invaluable, it sets up SR, resists Dragon while beating Magnezone, it walls Scizor with proper prediction, it nukes everything in Sun, it has ~8 sets that it can run. Hopefully that's all you need to know. If they removed the main Water and Fighting-Type Pokemon here, I would say that this would be the best Pokemon in the game. I never really used much or have trouble with the Specially defensive set, but it has been used to great effect so anyone can comment here.
Jellicent: I'm kinda on the fence with this one. It's really good in walling Keldeo and has a Water+Fighting Immunity, while being a good defensive spinblocker. However, it's kinda niche and has weakness to Pursuit while it can't really do much to a lot of Pokemon. I rarely use this but from what I've seen this thing is in limbo between A and A-.
Kyurem-B: Alright something I can talk about better now. Kyurem-Black can easily just knock a Pokemon out. If it sets up a Sub, it's pretty much game over for one of your mons. The fact that it is so easy to put someone in lose-lose situations just by getting Kyurem-B in is terrifying. It's the bulkiest dragon iirc with solid defensive typing that has a Water and Electric-resist which is invaluable against Rain. Of course this is a problem against Fighting and Rock-Types, but it really isn't meant to deal with them, as well as the fact that they can't switch in. Kyurem-B is also very diverse in role, it can function well on pretty much every archetype of a team as well. Of course, its susceptibility to being revenge killed pretty much forces it in A Tier.
Latias: Read what I said about Latios checking Sun teams and KelTarLando, just double that. Latias can possibly be the biggest problem to any Pokemon that it can comfortably resist. It is pretty much the most reliable Special Pivot in the game. It can function on Stall teams and Offense teams, either with it's LO set or the SubCM Set. It does suffer some issues with being giant Tyranitar fodder. As well as being really easy to wall with the Life Orb set (a lot easier than most people think) as well as having a Pursuit Weakness and
easy to abuse problems on the defensive set.
Landorus-T: Landorus-Therian is probably in limbo between A+ and A. It is the best Physical pivot in the game. With Stealth Rock, U-Turn, Intimidate, and amazing coverage, it is amazing at switching in while giving massive utility to the team while maintaining offensive momentum. Landorus-Therian also bodies DragMag teams. As it can tank most unboosted Outrages without being weak to Magnezone. It's typing is also really good for a wall. I also need to mention that Landorus-T has a lot more sets than people think. Rock Polish or Double Dance is friggin scary to deal with as a lot of people underrate that massive Attack stat of his and can easily catch guys off guard. Its massive weakness to rain and its lack of reliable recovery forces it down to A Rank rather than A+
Ninetales: Lowest weather inducer for a reason. It sets up Sun and doesn't do anything aside from that. Even then, it relies on Dugtrio/Gothitelle/Heatran in order to win the weather war. It is the centerpiece of an extremely powerful playstyle but is terrible standalone and relies on too much team support just to do its own goal. That just makes it quick.
Rotom-W: Rotom-W is good. It is a unique check to a lot of stuff and is very good at maintaining momentum with Volt Switch. It can run a few sets such as SpD Rotom or Scarf Rotom-W and can surprise guys like SpD Celebi by Tricking it, potentially rendering it useless. Rotom-W functions as a decent check to rain thanks to it's good defensive typing. Lastly, Levitate makes it an amazing check against a majority of Ground-Types in the tier. Rotom-W is probably the most annoying Pokemon that is viable right now.
Scizor: King of DPP, Powerful as ever. I honestly hope this is self-explanatory. Scizor is a solid revenge killer and hole puncher until now. It has good synergy with a lot of great Pokemon like Thundurus-T and has a really powerful priority attack. Scizor also can nab momentum with U-Turn really well as it can lure the likes of Jellicent in to get trapped by a Tyranitar, or U-Turning into Gothitelle when they send out Tentacruel (btw, Gothitelle/Scizor is brilliant) Of course, the fact that it gives Keldeo free switch in opportunities and it lacks a proper affiliaton with weather makes it drop down from A+ to A.
Starmie: Starmie is the best spinner. Offensive spinner is really good while checking Keldeo. It can also dent most Tyranitar with an offensive set given you can somehow make the opponent assume you are Bulky. It functions exceptionally in Rain and against rain, which is really good to have in the current meta. It does have some sorta 4MSS though while having a Pursuit weakness hinders it from A-Rank.
Volcarona: Alright everyone will probably disagree with me here. However, if you look at a lot of RMTs lately. Every single thing is 6-0'd by Volcarona (exaggeration). Volcarona works so well as an anti-metagame force in the current moment by smashing nearly every single sand team given it can get enough setup opportunities (weaken Keldeo) and HP Ground volc says GG to Sand Stall. Volcarona also can kill sun so easily while functioning in sun itself. It is most commonly seen in Sun but can also still be used in rain with Hurricane. Volcarona's SR weakness seems like too big of an issue, but the fact that most sun's team entire plan is to get SR Off the field makes Volcarona not struggle too much. Actually, it's biggest problem might be susceptibility to scarfers.
A-
Alakazam: An amazing safety blanket to offensive teams against opposing offensive teams. In a metagame where one needs to establish a superior offensive presence over the other offensive team, Alakazam flourishes as an offensive momentum disruptor. Alakazam does have some obvious flaws such as Pursuit weakness and it can't really do much outside of Sash but overall Alakazam is still good.
Breloom: Breloom was near S-Rank when it came out with technician imo. However, it really dropped because now, most teams easily have a check to it and it isn't too hard to deal with Breloom. Breloom does offer a ton of versatility and works really well on a lot of Hyper Offense teams. I personally don't see Breloom as a top tier threat anymore. However, Breloom is still really threatening.
Gengar:
Kyurem:
Mamoswine:
Salamence:
Skarmory:
Tentacruel
Venusaur:
