The people behind Super Mario Crossover have recoded Super Mario Brothers so you can play it with a bunch of different characters from other video games: Link from The Legend of Zelda, Samus from Metroid, Mega Man, one of the Contra guys, and Simon from Castlevania. If you showed this to me when I was a kid, my head would have exploded. Maybe literally.

To be honest, I haven't played with any of the other characters besides Link, because Link has always been the best video game protagonist ever. I love how the power-ups give you different swords; the high level of detail shows you that this thing was totally a labor of love.