Do we know that? They didn't actually say that it was a new Mewtwo form. Everyone seems to fully believe that because it's what Serebii originally said it looked like, but it hasn't been confirmed. It very well could be an entirely new Pokemon.
They did said it was Mewtwo, I don't know how Serebii didn't caught that
On the official Pokemon website they actually don't say that it's Mewtwo, they say that "it looks a lot like the powerful Legendary Pokémon Mewtwo, but not quite the same…" and "this new Pokémon shares many traits with Mewtwo, including a light-purple body and piercing, powerful eyes."
They're working pretty hard to not say that it actually is Mewtwo. My theory is that it is a Mew/Mewtwo fusion, like the Kyurem forms in B2/W2.
Stop covering for them. They specifically said new pokemon. THIS is not a new pokemon. This is an ugly mewtwo. After watching that mini trailer i'm quite sure that's all we get. Well guys let's brave another long and hard month before they decide to show us something else
Why don't you get over yourself a little bit?
How is this me being full of myself? Why dont you think of something better to say?
Superbot: Oh you want us to nerf Sackboy? Here why don't we break the game for you!