You will enter the room and the door will be locked behind you you
will see pyramid head taking his anger out on a zombie then he will
see you so get your gun out and shoot him to verify that your hitting
him you will hear the bullets hit the metal when he comes near you
don't let him hit you with his sword because one blow will kill you
run to the other side of the room and keep on shooting him and
eventually he will start to walk away down the stairs just leave him
and when all the water has been drenched walk down the stairs