Mewtwo

Mewtwo has exceptionally high base offensive stats and two separate Mega Evolutions which grant it great versatility and unpredictability to the point where it is nearly impossible to counter before its forme is revealed. Furthermore, Mewtwo sits at a Speed tier where it can outspeed the majority of the unboosted Ubers metagame bar some Deoxys formes. It also has access to a wide movepool, with many viable coverage moves in addition to moves such as Taunt and Calm Mind, which further its versatility. Mewtwo's abilities, while not particularly great, are all situationally useful. All this makes Mewtwo a formidable mid-game Pokemon that can break down opposing teams, with the potential to clean late-game as well. However, in spite of sky-high offenses, Mewtwo's attacks fall short of a lot of important OHKOs, and its typing leaves much to be desired defensively, being a bit lacking in useful resistances. Nevertheless, Mewtwo is a frighteningly versatile and powerful offensive monster in the Ubers metagame.