Although the transition to BW2 hasn't brought anything new for Yanmega, the truth is that it is still considered one of the best revenge killers in the tier and a very potent special sweeper. This fact is supported by its two abilities: Tinted Lens eliminates the opponent's resistances to Yanmega's moves, making its attacks even more powerful than they already were and lowering the effectiveness of its primary checks, whereas Speed Boost increases Yanmega's Speed to sky-high levels, causing Yanmega to outspeed every Pokemon in the tier after two boosts. Moreover, Yanmega's Bug- and Flying-type STAB moves are only resisted by Zapdos, Empoleon, Rotom-H, and Registeel, and its typing lets it get relatively safe switch-ins on a lot of attacks, mainly Grass-, Ground-, Bug- , and Fighting-type moves. This makes it excellent at capitalizing on Heracross, the number one Pokemon in UU, locking itself into the wrong move.
However, every Pokemon has its flaws: Yanmega has a terrible quadruple weakness to Stealth Rock that limits its longevity throughout the battle unless you pack a Rapid Spin user on your team. It also has a relatively shallow movepool and is very frail on the special side, going down to any strong special move. Overall, even though one might say Yanmega is outclassed by Sharpedo, it is a very threatening Pokemon that can rip teams apart if not prepared for.
Choice Specs Tinted Lens Yanmega speaks for itself: backed up by base 116 Special Attack, Yanmega makes best use of its ability to hit like a truck, making its name as a wallbreaker. Steel- and Flying-types might seem like good switch-ins for Yanmega, but all but Registeel do so only to be 2HKOed by a Bug Buzz, leaving Registeel and Snorlax as the only Pokemon that can avoid a 2HKO from Bug Buzz after Stealth Rock damage. The same effect, although to a lesser degree, is seen when using Air Slash, Yanmega's secondary STAB move, which has the nifty bonus of flinching 30% of the time. Psychic is useful to hit Crobat, Nidoqueen, and Nidoking for super effective damage or any Fighting-type if you don't trust Air Slash's 95% accuracy. As Yanmega doesn't have the greatest movepool, the last slot has two decent options in the form of U-turn and Sleep Talk. The former provides Yanmega with a quick getaway move and way to gain momentum and scout your opponent's initial switch-in. Alternatively, the latter makes Yanmega a very useful sleep absorber and one of the best switch-ins to Roserade, as it can take the Sleep Powder and threaten Roserade with one of the other moves in its arsenal.
Because Yanmega is in a very competitive Speed tier, a Timid nature is preferred to let it outpace Jolly Heracross and Timid Nidoking, while Speed tying with Jolly Darmanitan. However, if one is looking for absurd power, Modest can be chosen to hit as hard as possible.
Snorlax and Registeel must be eliminated in order to maximize Yanmega's effectiveness. For this reason, Heracross is a very good partner for Yanmega, as it smashes both sturdy walls with Close Combat. On the other hand, Yanmega can open up massive holes in the opponent's team, which Heracross enjoys and takes advantage of. Entry hazards are absolutely necessary for Yanmega to succeed, as they enable a lot of 2HKOs, such as specially defensive Zapdos and Empoleon. Rhyperior can set up Stealth Rock and take Rock-type moves aimed at Yanmega, while Roserade and Qwilfish can lay down Spikes effectively throughout the game. Since it is Choice-locked, Yanmega will be switching in and out often, so Rapid Spin support is mandatory. Blastoise can take Fire- and Ice-type moves thrown at Yanmega, Hitmontop soaks up Rock-type moves incredibly easily due to its resistance and ability Intimidate, and Kabutops forms a good synergy core with Yanmega, as the fossil takes Fire-, Flying-, and Ice-type moves and lures Grass-, Ground-, and Fighting-type moves, perfect for Yanmega to take advantage of.
This set makes excellent use of Yanmega's ability, Speed Boost. With Protect, Yanmega receives an automatic boost at the end of the turn without incurring any harm, meaning Yanmega will most likely outspeed the opposing Pokemon after using it. As stated previously, Yanmega's STAB moves in the form of Bug Buzz and Air Slash offer good coverage in the tier and hit very hard when backed up by Life Orb. Hidden Power Rock hits Fire-types, such as Arcanine, Darmanitan, and Rotom-H, and Flying-types, such as Zapdos and Crobat, for super effective damage, while Hidden Power Ground still hits Fire-types, but also the number one check to Yanmega, Registeel, for super effective damage. Giga Drain, however, destroys Swampert, Rhyperior, and bulky Water-types, such as Suicune and Blastoise, while also healing Yanmega.
As Yanmega is boosting its Speed at the end of every turn, a Modest nature is recommended to maximize its attacking power. Yanmega has a few viable options to run in the last slot: Psychic hits Crobat, Nidoking, and Nidoqueen for super effective damage, while Shadow Ball dents Cofagrigus and Mismagius. Roost is also viable to increase Yanmega's survivability, but is best used with its other ability, Tinted Lens. Heracross helps out Yanmega by removing its biggest nemeses, Snorlax and Registeel, while dealing with Empoleon, Crobat, and Zapdos accordingly after being weakened. Rapid Spin support is crucial, as Yanmega packs a quadruple weakness to Stealth Rock. Blastoise, Hitmontop, and Kabutops can perform the job easily and have good synergy with Yanmega. Finally, this set is very effective as a late-game sweeper. As such, entry hazards are required in order to weaken the opposing team. Rhyperior can lay down Stealth Rock, whereas Roserade and Qwilfish can put up Spikes on the opponent's field.
As previously mentioned, Yanmega has a very limited movepool. Hypnosis can be used to put one opponent to sleep, but its shaky accuracy leaves much to be desired. Ancient Power and Silver Wind have a 10% chance of getting a boost in every stat, but are weaker than Hidden Power Rock and Bug Buzz. Substitute is Yanmega's only way of avoiding status conditions and can prove to be useful as Yanmega forces a lot of switches, but its severe weakness to Stealth Rock limits the use of this move.
Checks and Counters
Stealth Rock is and always will be Yanmega's worst nightmare, as it will simply remove 50% of Yanmega's health just by coming onto the battlefield. Snorlax and Registeel are Yanmega's best counters, as they can take two Choice Specs Bug Buzzes after Stealth Rock damage and strike back with Return or Fire Punch or cripple with Thunder Wave, respectively. Zapdos resists both of Yanmega's STAB moves and OHKOes with any Electric-type move. Empoleon also resists Yanmega's STAB moves and can retaliate with Scald or Ice Beam, dealing massive amounts of damage. Crobat outspeeds unboosted Yanmega and can take one hit and retaliate with Brave Bird. Bulky special attackers such as Raikou can also take one hit and KO Yanmega easily with a super effective move. If Yanmega stands at +1 Speed, a faster Choice Scarf user, such as Flygon, Victini, Mienshao, or Raikou, can easily revenge kill it. Weavile and Honchkrow can also revenge kill Yanmega with Ice Shard and Sucker Punch, respectively.