The new costumes and models are sly references to other Nintendo games. They were also made from scratch.
Mewtwo's animations couldn't be imported from Melee, so the team spent an alleged 700 hours working on new animations for him. Roy went through a similar process, and both of their fighting styles have been revamped.
Forty-one playable characters, with a little taken from 64, Melee, and Brawl.
Mewtwo's final smash, Psystrike. Put simply, it's a one-handed, evil, massive Wave Motion Gun. If that doesn't scream Badass, then nothing ever can.