Super Mario Bros. Crossover is a fan project based on of Super Mario Bros 1. This lets you play as Mario or a character from another game. The characters currently available are: Mega Man, Link (The Legend of Zelda), Samus (Metroid), Ryu Hyabusa (Ninja Gaiden), Simon Belmont (Castlevania), Bill Rizer (Contra), and Sophia III (Blaster Master). The characters control essentially the same as they did in their NES era games. This can change your strategy considerably. For example, Mega Man cannot jump high enough to navigate many obstacles. He has to call on his robot dog to help him jump over them. Some characters cannot break bricks by jumping into them, so they must used their weapons. This changes brick breaking from a vertical to horizontal process. This sometimes makes things easier for these characters, sometimes harder. The game is amazingly well balanced, and all the characters are fun to play. They can also use the Mario Bros. power-ups with unique effects for each character. A lot of work and thought definitely went into this project.
Edit: One thing that isn’t clear is that you can save your game (press ESC to pause). Also, if you quit your current game after loading up a save file your unlocked cheats will remain.
Play for FREE Here: Super Mario Bros. Crossover.
Wiki/Manual Here: http://www.explodingrabbit.com/wiki/Super_Mario_Bros._Crossover/Manual