Shinobi

Invincibility

Press II, I two times, II at the title screen.

Sound test

Hold Select at the title screen until the sound test screen appears.

Level select

Hold Select after the "Mission Summary" screen. Then, press one of the following controller combinations when the screen turns black. Level Mission 1-2 II 1-3 II, II 1-4 II three times 2-1 I 2-2 I, II 2-3 I, II, II 2-4 I, II three times 3-1 I, I 3-2 I, I, II 3-3 I, I, II, II 3-4 I, I, II three times 4-1 I three times 4-2 I three times, II 4-3 I three times, II, II 4-4 I three times, II three times