Of all the original Pokemon, it's clear that Mewtwo was the biggest badass. The genetic clone of Mew, a sinister psychic monster capable of ripping through an entire team of high level Pokemon with just a thought. And now, you can add this unstable mutant organism to your own Pokemon Black / White team as part of an upcoming promotion.
Though the full giveaway details haven't yet been announced, it can safely be assumed that this Mewtwo will be the equivilent of the one given away in a recent Japanese promotion, sporting the special moves Psystrike, Shadow Ball, Aura Sphere, and Electro Ball. This Mewtwo also comes equipped with a King's Rock, which increases the chance of causing your opponent's Pokemon to flinch.
Again, Mewtwo isn't here yet, but have your Pokemon Black or Pokemon White cartridge ready to go, as the full details of this giveaway will soon be available on the official Pokemon site.
I'm personally a naturalist, I believe you should only train what you catch. When did the game's slogan change to "Gotta catch 'em all, unless they're only available as a gift promotion, in which case you don't have to catch that one"?