For about 25 years there's been a small but dedicated group of people making romhacks for Super Mario World, and the early stuff was pretty quaint -- mostly rearranging tiles and enemy placements to make new levels. But over the years people have done some incredible hacks with custom graphics, enemies, mechanics, you name it. I've played some of them on real Super Nintendo hardware with a Super Everdrive which allows you to load rom files to the cartridge memory from an SD card. It's amazing what some people have made.