After eliminating another devoted cleric of Iuz and his enhanced undead minions, we returned to glean more information from the beholder who informed us a little about the sucking wind teleportation trap; as well as the location of the Halls of Beckoning proper.
Upon reaching the halls, we broke into what looked like a summoning chamber through a not-so-secret door, where we found demons and the wizard Vayne, general of Iuz. We engaged them and the demons fell easily enough, but the wizard was inviolate until MMB saw through the illusion. At that point, another Vayne appeared with a much smaller demon; possibly his familiar. Although impervious to some attacks, this new Vayne appears to take damage; and we ended with the fight still raging.