Undead priest production

[llamabeast]

Go to battle with a load of priests in a huddle and some bog beasts on "guard commander" on one of the priests. Either carry the Ankh, or have someone cast Life After Death (if I've remembered the name correctly). The bog beasts will poison the priests to death, and then they'll come back to life as soulless priests. Magic!

[thejeff]

Summon Mound Fiends?

[SlipperyJim]

Yeah, Mound Fiends are probably the easiest way to get undead priests. I think that one of the Ice Devils is also an unholy priest, but I could be wrong about that....