Great job! It looks very nice but I see some flaws
1. Try making his arms 1.5 - 2 times thicker
2. Try making his toes closer together and his feet longer
3. You forgot the ball joint thing on his foot
4. Maybe make his chest area look more bulgey and muscular like abs
5. Make the start of the tail and the end a bit thicker
6. And maybe make the head a bit less "pointy looking"
7. I don't think his legs can bend if you know what I mean. I think it's like straight. (Can someone confirm this? In official pictures and the movie it's straight but in Melee it looks like his legs can bend)
Everything else looks fine but if you want to make Mewtwo from the movies then his thighs and tail is a lot thicker
Other than those i think your Mewtwo looks fantastic even without those changes.
And heres some reference I used from pictures and observing the movie
http://smashfan.com/characterimages/mewtwo.jpg
http://kxn.paperwaspnest.com/smash/image/mewtwo.png