Why didn't anyone think of this sooner? Mega Man Christmas Carol replaces the robot masters with the ghosts of Christmas Past, Present and Future, plus that poor old bastard Marley.
Dr. Light co-stars as an insane Santa Claus running the conspiracy. Mega Man Christmas Carol features no levels, just the boss battles. One question - what power does he acquire for defeating Christmas Past? A Mega Regret-Buster?
A Mega Man Christmas Carol [Sprites, Inc. via The Tanooki]