I don't get why you don't double smite him, have some other melee character or a caster with scorching ray finish him off. Haste potions are your friend.
If he's still alive even so, have a third finish the job. Your last guy can fight with your duergar allies. From then onward, you have your full team and the duergar. They're not more challenging than the redcaps at level 3 (or maybe I just hate the redcaps...). If you can't get through the mob towards Nere, there's not much you can do besides get backup or ranged explosives. Invisibility potions and Sanctuary, too. The ultimate time out card with a 100% casting chance, lmao.
