Don't you find it odd that you're slaughtering hordes of enemies in a small area? I thought of having set number of each kind of monsters and after having killed all of them in that area, you'd not be encountering them any more. Say, there's 15 Reindeer puppets in the area but after they're killed, there are no longer reindeer puppets to fight. After all monsters are killed, the screen is considered "safe" or "clear."