Mewtwo

Mewtwo's incredible stats and deep movepool grant it tremendous versatility and power. Its ridiculously high Speed, solid defenses, and access to Recover and Barrier make it one of the sturdiest checks to physical attackers that lack phazing moves, such as Mew and Earthquake Lugia. Offensively, its monstrous Special Attack, amazing coverage, and status moves allow it to threaten broad swathes of the metagame. Nothing is entirely safe from Mewtwo, though it may need to sacrifice itself with Self-Destruct to consistently eliminate the foe. Unlike most other threats of its magnitude in GSC, Mewtwo requires no setup before it can start blasting away. Mewtwo's flaws are few and far between, but the most exploitable is perhaps its lack of ways to deal with status. Paralysis is a death sentence for Mewtwo, which puts it in an awkward situation against foes with Thunder, Body Slam, or Thunder Wave. However, Self-Destruct gives Mewtwo a way to salvage even poor situations. Mewtwo is so difficult to handle that, oftentimes, players must resort to controlling it through Self-Destruct or Explosion, as a trade is usually preferable to continually enduring its attacks or being perpetually walled.