Use the following trick to quickly finish the fire arrow level of securing the bridge. When shooting arrows, choose a spot for the crosshairs that lets you shoot the arrows that come from different directions. When the Indians jump over the wall do not shoot. Run around the TNT then kill them with melee attacks. When Quick Killer appears, only shoot when he is right away from the barrels. You are better off just using melee and your flask. Quick Killer is not too difficult to defeat.