My build was: Promethean Magic, Fleshsmithing, Magic Training, Blood Magic, Demonologist, Killer Vegan, and Burglary. I killed him on Going Rogue with permadeath enabled. The build was very smooth sailing almost the entire way through. Zombies from Fleshsmithing made the first couple levels an easy clear, and made sure I didn't miss out on any xp from Killer Vegan. I leveled up Promethean until the Fireball (gives wyrmling as well which helped take aggro until I could level Burglary), then finished Magic Training - mostly for extraplanar concentration, but I took the last point since it gives some decent stats. I then took Fleshsmithing to the end for its heal, hp buff, and excellent source of alternate damage. After that I leveled Killer Vegan to get more regen, and tons of HP. I then got up to Abyssal Fire in Demonologist, which was nice for the extra fire resist. After that I finished Promethean, so I could spam Infernal Torus if I wanted. I finished Burglary after that, and took a handful of points in Blood Magic before killing Dredmor. Killing Dredmor was fairly simple after I had read about what he is capable of. I downed some potions for resist & extra hp, and some mushrooms for extra sagacity and whatnot. When he'd silence me, I'd pop a potion of purity, when he'd do his lightning bolt I would heal. If he got into melee I would blink away with the burglary skill, or go invisible (also from burglary). For damage, at first I chucked ~5 Holy Hand Grenades at him, sent a bolt of Mass Destruction his way, and a couple bolts of squid. In the end, Gog's Tactical Pyre did most of the damage to him. He generally stood in one place and cast spells at me, which I would happily tank with my 175-200hp and massive regen/heals, while I stacked up Gog's Tactical Pyres underneath him - each would do 2 ticks (don't know why 2 instead of 1) of about 28 fire damage each. I feel like this was a solid build, the only weakness perhaps being Demonologist. It didn't feel like a waste, but I felt like it wasn't as useful as another skill might have been. edit: Oh, and I forgot to mention - no aggro from animals evar! With lots of spells/summons to kill the animals and plenty of heals/regen aside from food, I didn't mind my inability to eat meats/cheeses.
It sounds like you didn't use Celestial Circle at all, which is hands-down the best skill in the entire Demonologist tree. Yes, it locks you down to one spot, but it also gives you spectacular surviving power.
