By pressing buttons 1+2 at the sametime during the Title Screen

Bonus Levels - Pause the game (by pressing run) and then press I, II, and Select all at once.

Clear pause screen - Pause the game and then hold I + II + Select.

Ending sequence preview - First activate the "practice bonus round" code and then highlight the Exit option and press II + RUN.

Practice bonus rounds - Hold II and then press run on the difficulty selection menu.

Remove Pause Text - Enable the Bonus level cheat. Highlight 'Exit', then press II +
Run. View Ending