At the end of mission 3, you will need to fight Johnny Vincent. The easiest way to beat him is as follows. First: When the fight starts he will be on his bike holding a pipe, he will rarely attack you but it will hurt so try to avoid him. Second: Don't help Petey over to the crane, let Johnny stay on his bike. Third: Use the super slingshot to repeatedly hit Johnny until he is at low health or knocked out. Fourth: If he's just at low health, you can help Petey get to the crane, their are several greasers blocking him, hit them with the super slingshot, when Petey reaches the crane it will pick up johnny and his bike and leave him hanging by one hand, just aim and fire the sling shot at him until he is done.