6 THE WATCHER IN THE WALLS. The Watcher will be here.
The Watcher In The Walls (AC 0; MV 9”; HD 10; hp 50; #AT 1; D 1d12; SD Magic weapons needed to hit, limited spell immunity; XP 2950)
If the Watcher is defeated and the adventurers stay in the room, after one turn they will see a reborn Watcher squeeze through a crack in the north wall. This is a dead giveaway about the presence of the secret door.