Immortals and cursed items

[Taqwus]

Saurolich... needs to die... hm.
Got death gems? Try lammashastas; they don't like their summoners either. There are other battlefield spells and summons that can hurt yourself, too. Or putting him far forward on 'attack' surely should help. Or script big spells so he falls unconscious.
There are also remote rituals that don't discriminate; for instance, Flames from the Sky hurt friendlies, too (or at least in Dom I it did); dunno if Fires from Afar does as well. Ghost Riders, horrors also don't care who they attack.