Change Speed
This cheat works on the demo as well as the retail version (has to be version 1.1 or later). Type GUBBLE (demo) or GUBBLEDCHEAT (retail version) at the title screen. You will hear Gubble D. Gleep laugh, then during play press the + and - buttons to adjust the speed.
Level Select
This cheat will only work with the Full Version. Add the Title Screen type GUBBLEDCHEAT, you will hear Gubble laugh. Go to a Launch Pad and press:
Home-Warp ten levels ahead.
End-Warp 10 levels behind.
Page Up-Warp to next level.
Page Down-Warp to previous level.