This is like my magnum opus of 2007 in Super Mario hacks. Long before there was Super Mario Maker for Wii-U, there were hackers who made graphics and level editors for a lot of the different roms out there available, such as the Super Mario Bros trilogy.
You basically edited the actual game rom, and any device or cartridge that played roms was compatible with your hack. I used a powerpak for NES and played it in a real nintendo, but there are also everdrives and all sorts of other devices.
The level editor for Super Mario Bros 1 let you change environment effects as well as other stuff. So I chose one that didn't fit with the underwater level type and suddenly everything was green and pink. There were other things I had messed with, like a full castle background much like 8-3 of the original, but with red brick instead.
This is the only hack I had made that has the full game. I hope to make more later on though its been several years, and even begin the very difficult to edit (it seems) Super Mario World.
Be sure to Download: Mario1.zip
Check out some screenshots: