[Taqwus]

Demon Lords are pretty buff, and make decent battle mages, but they can't wear armor and are just as vulnerable to Curse (Increases affliction chance, no MR check, requires Astral/Nature) / Vision's Foe (Takes out an eye, no MR check; requires Death/Air) / Bow of Botulf (Feeblemind, no MR check; requires death magic) as anybody else. Curse is a nice counter for supers in that it greatly increases the chance of getting an affliction when wounded, and it doesn't matter that much how powerful you are if you're blind and feebleminded.
They'll still be KO'd by Magebane, but that's an artifact...