Other playable characters (Skins) automatically become unlocked when you complete the corresponding task during gameplay.
Unlock Classic Hulk:
Collect 5 comic book covers.
Unlock Grey Hulk:
Destroy 10,000 objects during the game.
In each New York neighborhoodn destroy at least one building.
Defeat the U-Foes using a deceptive ploy so that a U-Foe defeats his own teammate. Also defeat the Abomination
Unlock Professor Hulk:
Complete ALL the Jump challenges.
Added by: Sanzano Jun 12th 2008, ID#30308