Just wondering, is there a current list of most common lead-offs in UU right now? (If so, could you post a link?)
No particular order:
Hariyama: Can Fake Out and activate a Toxic/Flame Orb at the end of the turn, activiting guts and dealing out heavy damage with Close Combat. Is a pretty good lead counter to Omastar and has the bulk to survive later.
Ambipom: Can Fake Out / Taunt set up leads, sometimes carries Technician boosted Grass Knot for Omastar, and can smack things around with STAB Return. High Speed makes it an excellent revenge killer thanks to Fake Out. Because it can be used for revenge later, it often uses U-Turn. The most common set is likely "Fake Out/U-Turn/Taunt/Return or Pursuit or Grass Knot.
Mesprit: Can set up Stealth Rock and U-Turn out, and has the bulk to take a few hits, serving as a Torterra counter later. Can run Choice Scarf or Choice Band sets with Trick/U-Turn/Zen Headbutt/Stealth Rock, which can completely ruin other leads. With a Choice Scarf, it is fast enough to outpace most leads, but still slow enough to be able to U-Turn away from Uxie if it carries a Choice Scarf itself.
Uxie: Has the general bulk, as well as a wide array of support moves. Stealth Rock/U-Turn/Memento/Yawn/Toxic/Thunder Wave/Reflect/Light Screen can all be used on sets, making Uxie extremely difficult to stop. Has a decent variety of attacks such as Thunderbolt and Psychic, and can run Choice Specs/Band/Scarf. The Scarf set is primarily focused on Trick early.
Venusaur: Mainly used for Scarf Sleep Powder, but can be used to play "mindgames" as well, including Leaf Storming turn 1. Is an excellent stopper to Cloyster, Omastar, and Kabutops, preventing Spikes or Stealth Rock. Can carry Hidden Power Rock or Psychic for Moltres or Toxicroak, and with a Choice Scarf, can outspeed them both.
Moltres: Mainly the Life Orb variety are used, purely on how strong it is. Hidden Power Grass OHKOs Omastar and Kabutops, and Fire Blast can O-2HKO most other leads. Air Slash hits Hariyama fairly hard, maybe enough for a OHKO. The reason for using this as a lead early is to beat stall teams easily; They will likely bring in Chansey, giving you an easy chance to bring in Dugtrio, who will OHKO with Beat Up. Another positive is that it won't have to take SR damage (50% off its health) if it wants to play.
Omastar: Classic Spikes Lead, can beat Ambipom easily if it doesn't have Hidden Power Grass, although Amb can Taunt back preventing Spikes. The selling point is obviously Spikes, which can be invaluable to Stall or Offensive teams. Also beats Lead Arcanine.
Spiritomb: Mainly Choice Banded, as it can Pursuit Ambipom, who will likely Taunt, for a 3 or 2HKO, depending on your spread. This leaves Ambipom useless. Uxie and Mesprit can do almost nothing, and Shadow Sneak can revenge kill lategame. The main selling point here is Trick, rendering many Pokemon - such as Cloyster or Omastar - useless. Will not prevent a full layer of Spikes.
Alakazam: Can OHKO Omastar, Cloyster, Kabutops, Nidoqueen, Hariyama and almost any other lead (with a few exceptions such as Spiritomb) with a moveset of Psychic/Grass Knot/Counter/Focus Blast. Alakazam's "Inner Focus" prevents Fake Out from flinching, allowing it to defeat Ambipom fairly easily, usually using Counter on turn 1. Uxie and Mesprit that use U-Turn, expecting Taunt, will find the next switch-in being blasted by Counter, usually weakening it enough to be killed with Zam's next move.
Cloyster: Can Spikes, Toxic Spikes, Rapid Spin, and Explode. Usually not all 4 moves will be found on the same set though. With a higher speed than Omastar, as well as higher Defense, it can withstand a bit more of a beating. However, it's Ice typing gives it horrible weaknesses to Rock and Fighting. Low Special Defense makes it a risky lead to try and get 3 Spikes with.
Kabutops: Swift Swim allows it to combat Rain Dance teams almost right away, and can spin away Stealth Rock fairly safely, as Stone Edge will severely dent any Ghost-types. Aqua Jet can be used for revenge killing purposes and Kabutops usually has Stealth Rock itself so it can do something.
Rhyperior: A good ability and good stats, as well as STAB Earthquake, allow it to combat many leads such as Omastar and Ambipom. Can Stealth Rock as a lead and not be useless. Stone Edge also receives STAB.
Arcanine: Not as common now but still sometimes used, with Fire Blast/Toxic/Hidden Power Grass/ExtremeSpeed. Intimidate weakens many of the Fake Out users too much to do any real damage and the Fire-type can lure Omastar into a false sense of security as HP Grass OHKOs. Toxic is used to weaken the really bulky Waters, as well as Uxie or Mesprit, as the rest of the team usually thrives with these 2 gone. ExtremeSpeed is used mainly for Focus Sash purposes. Morning Sun can be used over Toxic for survivability. Like Moltres, won't have to fear Stealth Rock right away.
Nidoqueen: Still being used, but not very useful. Can Taunt/Toxic Spikes to threaten Stall teams, and has a high enough Defense/Poison Point to threaten Ambipom. Earth Power does enough to Omastar to stop it quickly. Is not able to even scratch Uxie or Mesprit really.
Hippopotas: Not very common, sets up Sandstorm and Stealth Rock.
Houndoom: Not very common, but is very powerful. With a Scarf set, it can Dark Pulse/Fire Blast/Hidden Power Rock most of the other leads right away and KO them. Protect/Sucker Punch/Fire Blast/Dark Pulse can scout Fake Out and hit very hard back. Can also use Taunt and Counter, similar to Alakazam.
Snover: Not very common, sets up Hail.
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Many more, I'll work on those later.