Cheat mode:
Pause game play and press Up, Down, Up, Down, Up, Down, C, B, A, Right, Left. The music will resume to confirm correct code entry. Enter one of the following controller actions to enable the corresponding effect.

Level skip
Press B.

Slow motion
Press A. Press Start to return to normal speed.

Cheat mode (Japanese version):
Quickly press A, B, C, A, B, C, A, B, C at the option screen. A sound will confirm correct code entry. This will allow you to select the "easy" difficulty setting which features an "omake" stage.