Updated: Oct 19, 2020
Recently a know Sega Genesis/Megadrive programmer by the name of TiagoSC on the NESDev forums released a tech demo of Sonic The Hedgehog's stage 3 in Green Hill Zone for the Super Nintendo.
This is no simple sprite swap or romhack. This game was developed from the original code from the Sega Genesis version of the game! To see it in action and a comparison to the same stage on the original Genesis version check out my video here. The game can be loaded up on a SNES flashcart and played on original hardware! There were a lot of tricks involved in getting this game running on the SNES. As it is just a tech demo it is missing some things like sound effects. But overall it is very neat to see this and play it on the SNES.
If you would like to try this out for yourself. Download the rom here.
Buy a flashcart from Stoneagegamer here.