Zapper

Auto Hop (Hold D-pad to keep Zapper moving)
Collect all 400 fireflies in level 3.
(Thanks to rabidmoogles@hotmail.com)

Get Extra Lives
On the level "Voodoo Choo Choo", make your way to the front of the train where you will see a giant eyeball. Zap the eyeball four times to get 4 free lives.
(Thanks to rabidmoogles@hotmail.com)

Infinite Lives
Pause the game, hold L and press Up, Up, Left, Left, Right, Left, Right.
(Thanks to rabidmoogles@hotmail.com)

Infinite Shield
Pause the game, hold L and press Up, Down, Up, Left, Right, Down, Up.
(Thanks to rabidmoogles@hotmail.com)

Infinite Super Zap
Collect all 400 fireflies in level 4.
(Thanks to rabidmoogles@hotmail.com)

Insect Eye (Changes your vision)
Collect all 400 fireflies in level 1.
(Thanks to rabidmoogles@hotmail.com)

Screen Switch (Reverses level)
Collect all 400 fireflies in level 2.
(Thanks to rabidmoogles@hotmail.com)