Hey man, this is my first time on this forum, so forgive my english. You are supposed to be using the soul swords to fight him, when it says impale him, it means stick it in him, in other words, press R2 to throw it at him. It will plunge itself in his stomach. You have to go get the other sword and fight him for a bit more till it asks you to impale him again. Make sure you are standing in front of him, facing and press R2. That throws the weapon. Good luck.