Level skip:
Press Right, I, Left, II, Up, Select, Down, Select at the title screen. A sound will confirm correct code entry. Hold Up/Right and press I + II + Select during game play to jump to the next level.

Sound test:
Press Left, Right, I, II, Down, Select, Up, Select at the title screen. Use the D-pad to display a two number sound code at the bottom of the screen. Then, press I to play the sound, or press II to reset the sound to zero.