Mesopotamia

Final Boss battle:
Hold Down + I and press Run at the "Input your birthday" screen.

Sound test:
Hold Up + I and press Run at the "Input you birthday" screen to display the sound test menu. Note: The duration that Run must be pressed is very precise.

Adjust brightness:
Enable the "Sound test" code. Press Select, Up, Up, Down, Down, Left, Right, Left, Right, II, I at the sound test menu.

Mini-game:
Enable the "Adjust brightness" code. Press Select until a flashing red screen appears. Then, press II, Up, Up, Down, Down, Left, Right, Left, Right, II, I. Use the D-pad to move, II to shoot, and I to fire a smart bomb during the mini-game.

Monochrome mode:
Press Select fifteen times in level one during game play. Press Run to pause game play, then hold I and press Up.

Unlimited extra lives:
Pause and resume game play one hundred times. All enemies that are shot will turn into bonus lives.