Sonic 1: Return to the Origin is a romhack of the original Sonic the Hedgehog game on Genesis. It modifies the original game in which each level has to be played backwards from the end of the level to the beginning. This also means bosses have to be fought at the start of every 3rd act before Sonic can continue on through the level.
CyanTheGamerhog01 makes their way through the reversed levels without making use of any glitches. This includes No Zipping, No Level wrap, No Slope glitch, and No clipping through solid floors.