Pokemon Red and Blue
Mewtwo is the star of the first pokemon movie, the highest level legendary pokemon, and the "king" of the Kanto region. He's technically a veteran, but didn't appear in Brawl. Most fans don't know that he was planned on being in Brawl, though. Hackers found a file for his victory theme and a final smash sound effect. It's even rumored that the "random character" space in Brawl was supposed to be Mewtwo's space.
For obvious reasons, most fans believe that Lucario "replaced" Mewtwo. This however, is obviously not true. The only move they share in any way is their standard "b" move. Other than that, they have no similar moves. For this reason, I don't believe Mewtwo should have any moveset changes in the next Smash Bros. game.