So, I just wanna say right now, I don't think that thing is Mewtwo. I haven't been calling it Mewthree or anything (actually I've been calling it MewBuu xD), but I definitely think it's a new standalone. I actually agree with the theory that it's another clone of Mew, possibly trying to improve where Mewtwo failed, namely the obedience problem. That's actually why Giovanni was so hellbent on getting the Master Ball in Red/Blue, so he could finally control Mewtwo. Just looking at the NewMew's picture actually seems to confirm my theory, too, given that the eyes are somewhat lifeless and void of sentience.

Part of me wants to say this will just be a side legendary that you don't need to worry about, but I REALLY REALLY REALLY want it to be a big part of the story :3

D:< I ALSO WANT TWO SAVE FILES ON MY POKEMON GAME xD

anyways, I'm soooooo looking forward to Pokemon X/Y. Gonna start with a Froakie, then I'll play it again with a Chespin. :D