There is a secret password zone in the about dialog box.
Hold the shift key and click on the black pixel of the right eye on the
image of Bug. A dialog box will appear. Click in the box, type BABYSEALS,
and click either the WOW! or YIKES! boxes (*not* the OK box).
Now there is a new menu to the right of the Help menu. It does not
show anything, but when the blank area just to the right of the Help
menu is clicked, a new menu drops down with the following on/off choices:
Level Skip - Duck/Crouch plus Up = skip forward one level
Duck/Crouch plus Down = skip backward one level
Flying Bug - Press Y to lift off and direction controls to move
Note: If this is checked, the Level Skip cheat also works
Invincibility - Enemies go right through Bug without hurting him
Hitpoints - Bug reacts as though he's been hurt, but no hitpoints