How about giving Mega Man the ability to use special weapons that the Robot Masters used? The catch is... Mega Man's available special weapons are influenced by and are dependent on his opponents.
For example, if Mega Man is in a match against Pikachu, Medusa, and R.O.B... then Mega Man's available special weapons are from Sheep Man, Snake Man, and Top Man (instead of tops, he shoots gyros).
Or if Mega Man is in a match against Mii, Takamaru, and Ice Climbers... then Mega Man's available special weapons are from Strike Man, Shadow Man (well, he throws shurikens), and Ice Man.
And if Mega Man is in a team match where he is teamed with Little Mac against Pit and Duck Hunt Dog... then Mega Man's available special weapons are from Centaur Man (well, he shoots arrows) and Hornet Man (with ducks instead of bees). If Little Mac were an opponent, Mega Man would have gotten Hard Man's special weapon.
To switch special weapons during a match, press either direction on the D-pad. What Mega Man lacks in taunts, he makes up in an unique gameplay experience.