I'm a little late to the party, but I'll go on ahead. Mewtwo's swimming animation should have him cross his arms and telekinetically swim, and his drowning animation would be him calmly splashing in the water, because nothing scares Mewtwo, not even teetering on a ledge and looking straight into a bottomless chasm with only your toes keeping you from falling to your death. His sinking animation would have him put his palm in front if his mouth and his hand up as he plummeted downward, and his rising animation would have him telekinetically swim upward, without moving his feet or legs.
As for Mewtwo being a clone, not only do I highly despise the idea, I see it as highly unlikely. I mean, 5+ months on one character's gotta mean something, right? He won't be a 5-minute copy-paste like Dark Pit, and I don't think he'll be a clone by any stretch of the imagination. He will be his own character, with an original moveset, like he ought to be.
And before people shove a brick down my esophagus about Dark Pit, let me say that I think he's an awesome character from what I've seen and heard. I like his personality and concept a lot. I just think Sakurai should have done a better job with his moveset, or even just left him out. There's a far more deserving rival-type character who could've been in, anyways. *Cough-
-cough*