Sonic the Hedgehog in Super Mario Bros.

As the name suggests, this ROM hack replaces Mario with Sonic, with the rest of the game left relatively untouched. Sonic always runs, regardless of whether or not you’re holding the B button, all of the texts are changed from Mario to Sonic and Toad now gives you a useful tip.

Story:

Do you have what is takes to save the Mushroom Princess?

You'll have to think fast and move even faster to complete this quest! The Mushroom Princess is being held captive by the evil Koopa tribe of turtles. It's up to you to rescue her from the clutches of the Koopa King before time runs out. But it won't be easy. To get to the Princess, you'll have to climb mountains, cross seas, avoid bottomless pits, fight off turtle soldiers and a host of black magic traps that only a Koopa King can devise. It's another non-stop adventure from Sonic the Hedgehog!