At the end of a second runthrough with the improved Mardracht. It's difficult to tell because the game doesn't really signal when it's applying resistances, but is sure seems like he's resistance to non-magical weapons, just like the wights. I get that he was too weak before, but it was a rough fight anyway, and with all this resistance, chewing through his 90hp is a chore. And if he decides to pop his fear bubble, it's all over, since my guys basically can't hit a DC20.
I'm sure a wizard would help, but I didn't bring one this run, and mostly haven't missed them. But there may be walls you just can't get past. Unless there are some magical melee weapons laying around somewhere I can use to help out with this fight. I've yet to find one on either run.