I don't know about Mewtwo, are they really going to waste another trailer on the Pokemon franchise? It was in their best interest to just put them all in one trailer. Jigglypuff doesn't need one, but Mewtwo most likely did.
I don't know where people got the idea that Mewtwo is coming back but if he does, most likely it won't be revealed until the game is out. I don't see Sakurai revealing more Pokemon after the Direct. He's got to keep some characters a secret until the game is out.