WOW!!! Greninja. Cool! While it does unfortunately look as though he will replace Mewtwo, he looks like he almost makes up for it. I don't know if one of these has been posted before, but here's an analysis of is move-set I came up with:
Neutral Special-Water Shuriken (Most Likely) . Appears to function similar to Aura Sphere. One of the reasons he would replace Mewtwo.
Side Special-Extra-Sensory (?). Appears to function like Pikachu's Quick Attack. Likely a phenomenal recovery move. May have the "wall-grab" ability of Lucario's, considering his nature.
Up Special-Smoke Screen (?). Appears to function like Mewtwo's teleport, but with damage at least at the end, possibly the start. One of the reasons he would replace Mewtwo.
Down Special-Substitute (Most Likely). Appears to function like Double Team. Less Risky. Looks like the attacking it triggers a seemingly unavoidable attack, either a default move or you can attack out of it, like Teleport in Project M. May deal some damage to Greninja to seemingly unavoidable nature if you take the bait.
Final Smash-Night Slash (?)-Appears to function like Ike's. Very cool.
Physics In General-Apparently astounding jump height, very quick attacks, and probably at least one good finisher, namely the one with the Aqua-Knives. Seemingly heavy emphasis on combos, namely aerial ones. Most likely astonishing recovery ability. Most likely one of the fastest characters in the game, ranging somewhere from 4th-2nd. Likely a middle-weight character. Very low crouch. Probably normal standing height. Most likely can crouch and wall cling, judging from the nature of him.
He's my new main, assuming Mewtwo doesn't come back. New favorite smash character (second if you count Mewtwo). Also, I think we've found our new Meta-Knight.