Mega Man: Day in the Limelight 2

Mega Man: Day in the Limelight 2 is the second game in a fangame trilogy based on the 8-bit series of games, and created by Riverroad. Story-wise, Mega Man has either disappeared or become unable to beat Dr. Wily, and it's up to past Robot Masters to save the day. While the basics function much the same way as traditional Mega Man games, each character has different attributes, from movement to attack patterns and even special abilities! The idea was novel enough to warrant further sequels, improving on the formula. MMDL2 in particular allows you to play as the conquered Robot Masters in subsequent stages, among other secrets.