I remember a game i used to play title escapes me right now, but the twin matched you move for move you attack; he attack, you heal; he'd heal but it was one of my favorite battles of the game. now im going to have to go try and fig out what game and play it again
Are you thinking of Zelda 2: The Adventures of Link for Nintendo?
... but of course, your "evil twin" would have blue phasers on his starship.
... and his Galaxy class ship would separate saucer and body properly.
... and he would level up mid fight over the current cap !