Sigma with his beam sword... Nah! there already is a chance this game will be sword heavy. Sigma from X2 with his wolverine/(strikers version)bowser type claws gets my vote! although his battle armor from X1 would make the better final strike. Giant wolf-looking robot shooting flames, electricity and slashing claws FTW.
also may i add, i don't like the idea of having 3rd party characters as antagonists in the single player. I'm not opposed to any being in the game, i just wouldn't want Smash to become a “Nintendo vs ...” affair