Dungeon: Serpent's Skull Catacombs

I recently did a quick build for a small catacombs dungeon in Serpent's Skull of my own design. The actual encounter just said that the players have a encounter with a strong undead creature. I put in my own twist and decided this undead must have some sort of lair. Since he has control over animals I figured that a way to retreat back to his coffin (it was vampire-like) would be handy. So I placed four special tiles in the dungeon that when stepped upon by living creatures would open the door to his inner sanctum for a round or two. He would mindcontrol four spiders to do this for him, the players would have some issues though.

The fight was rather awesome and in the end they did manage to invade his sanctum and slay the undead. Much better then a random encounter with the undead creature.

And a quick shot of the setup: (Notice the mixing of my tilesets, the new and old one)