Hermit: an always-generated-peaceful, sessile human monster. Possibly only one can generate per game. He or she collects books and will ask for books when chatted to. In exchange for each book, they dispense a rumor which is false if the book was cursed and true otherwise.

A more complicated extension is that rather than simply taking the books, they could instead stash them into a magic-chest-like extradimensional space, the contents of which show up in an identical chest in the Wizard’s Tower. The significance of this is left up to the player’s interpretation.

Create a procedural level generation algorithm for tower levels, particularly Vlad’s tower. Vlad’s tower should also be larger on the bottom than it is on the higher levels.

Make the Wizard’s Tower its own level(s) rather than embedding it in Gehennom.

Remove the beehive from the Wizard’s Tower. Bees are too easy for a late game player. If, instead, it should be kept (maybe a Wicked Witch of the West reference?), the beehive should open into the central area of that floor, so the bees can come out and attack the player.

Redesign the Wizard’s Tower so the hero enters in the southeast corner on the bottom floor, spirals into the center with the upstair, the second floor has the downstair in the center and spirals out to the upstair in the northwest. The top floor has its downstair in the northwest and basically the same layout as now.

Remove the Fake Wizard’s Tower special levels. Instead, there is simply a doorway you can walk into on the bottom floor of the normal Wizard’s Tower. (If it’s desirable to keep the fake towers, let them be randomly generated features in Gehennom.)

Inside the Wizard’s Tower, the player encounters some of the Wizard’s hostile apprentice wizards.