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

Enter these cheats at a code terminal in the game:

Play as Gray Hulk: JANITOR
Unlock Desert Battle art: FIFTEEN
Unlock Hulk Movie FMV art: NANOMED
Unlock Hulk Transformed art: SANFRAN
Unlock Hulk vs. Hulk Dogs art: PITBULL