Even if extracting NES game data is not your thing, the emulator concept [Matthew] uses might be still worth a read.

The final Mario Maker 2 update lets players create up to eight worlds with a total of 40 courses that can be combined into one mini Super Mario game that users can create and share with others.

You can create music levels that play songs, puzzle levels that switch up the traditional roles of Mario and his nemesis Bowser, homages to other games, and much, much more. There is one constant ...

With Mario Maker, you can create and play your own levels in the original Super Mario Bros on Nintendo's newest game console, the Wii U. "It was fast and seamless.