Options screen:
Press Select at the title screen.

Level select:
Enable the "Options screen" code. Hold II + Select and press Run at the options screen. Use I and II to change the brightness of the screen.

Level preview:
Enable the "Options screen" code. Hold Select and press Run at the options screen. Use Up and Down to preview the levels.

Sound test:
Enable the "Level select" code. Hold II + Select and press Run at the level selection screen.

Extra credits:
Hold Select and press Up at the continue screen for an extra continue. Alternately, press Select on controller five for up to nine continues.

Unlimited credits:
Press Up + Select + I + II during game play to increase your credits to nine.

Pause game:
Hold Run on controller five to pause the game.

Sound test:
Enable the "Level preview" code. Hold I and press Run at the level preview screen.