Metroid II: Return of Samus
Metroid II: Return of Samus has been hacked.
M2Edit is a Metroid II editor that can edit the tile arrangements and the tiles themselves, as well as the maps of each room.
Metriod 2 DX is a hack of Metriod II: Return of Samus that makes the game use color palettes.
A debug menu exist in Metroid II: Return of Samus. It allows some game items to be obtained, and change beams, via a very simplistic menu via pausing the game (with the debug menu flagged). There's also a feature that lets you save anywhere, by pushing Select while paused. After pushing select, the game will resume, without sound. Push Start twice to return to normal. This RAM cheat can access that menu.