Enable Sound Test cheat. Press I, II, than keep pressing Select until the debug screen appears.

You can now do the following:

Code Effect

Use level select to go onto which level you want, then hold I and II and press Start to begin gampleay with 10 lives and 10 bomb Extra Lives, Bombs, Power
Enter 83 Half Game with lots of Satellites
Enter 77. Press Up, Down before leaving debug screen. Invincibility
Enter 00 (level 0) - 09 (level 9) Level Select

Select Difficulty - After selecting your mode, press Run and Select simultaneously to reset the game.

Code Effect

Place I and II on top turbo speed and hold down I, II and Select simultaneously ''Normal Dog'' or ''Hard Human'' difficulty

Place I and II on low turbo speed and hold down I, II and Select simultaneously ''Super Mania'' or ''God of the Game'' difficulty

Sound Test - Hold Select and alternately press Left and Right repeatedly until 'Sound 01' appears.

Code Effect

At the title screen, hold Select and press Run until the phrase 'Area 1' appears. 30 Continues

Enable the Sound Test cheat. Press I, II, Select 22 times. Then hold Select and Run until the game starts. Area 0, 30 continues

Hold Select and alternately press Left and Right repeatedly until 'Sound 01' appears. Sound Test
Hold Right, and keep pressing Run quickly at the title screen.