It's time to try and escape from the castle. The exit is pretty much right ahead of us but one door will block our way, a door that is quite locked indeed. That floor is a boss floor, the only ones where a key is held by a unique boss enemy that appears only on that floor (with a few very notable exceptions). The only way to get the key is to kill the boss and each one is a very challenging enemy who is more then capable of killing you quickly. Strategy is needed to take a boss down effectively as well as making every shot count..