Ermor?

[Endoperez]

I don't think undead actually take more damage from fire. Mummies do, but the ones that come in huge numbers (longdead, spectral whatever) don't.

However, there are lots of Fire (and Astral) spells that deal extra damage against undead, e.g. Holy Pyre. Incidentally, Holy Pyre doesn't harm Devils...

Devils rule over undead because they have so good stats that, even with superior numbers -> more hits against the devils, the undead can hardly even harm them. I imagine Fiends of Darkness would work just as well, or at least come very close.