When you come out of the Troy Undergrounds you must fight the 9 headed monster. When doing this, use the spear then the Power Of The Gods. Stand out in the open. When one of the heads is ready to strike, go behind one of the pillars. The monster will strike and try to bite. Press Circle to chop off its head then get one of the fire arrows and shoot the neck. It will explode. Do this repeatedly to kill it.