Mewtwo also have a great move pool to play around with. I've already started deciding what all he should learn for a nice, well-rounded moveset. But, yeah, he's un the uber tier, and thus is usually banned.
You know, if you're a real competitive player who's worth your salt, you wouldn't give a fig about tiers and would find ways to beat teams that use upper-tier Pokemon, rather than pussy out and ban them. Banning them from play is the coward's way.