Enter these cheats at the code input screen in the Options menu:

Double Health for Enemies - BRNGITN
Double Health for Hulk - HLTHDSE
Half Enemies' HP - MMMYHLP
High Score reset - NMBTHIH
Invincibility - GMMSKIN
Level Select - TRUBLVR
Regenerator - FLSHWND
Unlimited Continues - GRNCHTR