Its simple.Heres what you must do.When the large monster attacks, what you need to do is shoot the large statues beside the levers to get his attention. Pick a close one, either left or right and fire at it until the creature notices. When he does, his head will lower and look at it closely. When the creature does that, immediately use the grapple and snag the level. Pull it back and a set of spikes will drop down on its head. You need to do this three more times and the creature will be no more.