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I mentioned a few tactics. Easiest is to simply polymorph (through wand, fountain, magic mushrooms... there's plenty of ways). Even without polycontrol, you may polymorph into a pretty powerful character. "Elite Dark Knight" is the one I usually go with if I do have polycontrol. Then he's a piece of cake.
The other method is to lay traps outside of his door, and drop some food behind the trap. He'll come to eat the food and damage himself. If you can get him to lose both his legs, again, he'll be easy