Hold Select at the title screen until the word "Hard" is displayed.
Level select
Hold Run and press Select three times when the house and lightning are displayed on the title screen. Then hold Down/Left and press I. Note: To face the final Boss, select level 0.
Level select (Japanese version)
Press Select three times, then hold Left and press Run when the house and lightning are displayed on the title screen. Note: To face the final Boss, select level 0.
Sound test
Enable the "Level select" code. Then, press Select at the level selection screen.