Killing Demons

[Valandil]

For what its worth, marignon has a national holyfire spell that does extra damage to demons, and there is an artifact called the bell of cleansing that zaps a demon every turn.

Herald lances, flambeaus, demon banes, cleansing water, banishment, smite demon, apotropaic sword, apotropaic trident, and a few special sites, all have effects that kill demons.