When a player character is deaf they're unable to cast any spells. It would be interesting if you could to apply the same effect on monsters with thrown potions of deafness, so their spells and summoning abilities are disabled for a number of turns. There should be a chance for the effect to fail depending on the target, so you should very rarely if ever be able to disable the ACW or Nuurag.

This would make for some strategic depth, i.e. do I get close to that emperor lich to throw a potion on it (and risk getting surrounded), or do I stay at a doorway and kill off the summoned mooks one by one...