Shinobi III: Return of the Ninja Master

Shinobi III: Return of the Ninja Master is, as you'd expect, the third game in the Shinobi series.

...Except it's not. Hm.

Character Editor
Pro Action Replay code enables a character editor which can be accessed by holding B + C and pressing A. You'll see a bunch of crap appear onscreen and the words "CHARACTER EDITOR 3.52" under everything.

The character editor allows you to modify the VRAM. You can redraw individual sprites and change the color palettes. Press Start to restart the game and ignore the changes, or hold B and press Start to save the changes and proceed.

The code also allows you to access the editor from anywhere in the game. Interestingly, it still resets the game when pressing Start rather than going to the memory and level editors.