Easiest way to kill Mor the Trenchmouthed on Bloodmoon Island

This is often a tricky fight and many players skip it in honor mode because Mors ability to possess you can throw a wrench in your plans. The most common way to deal with him safely is to use summons to fight him while your team hangs back. But tonight I found an even easier way.

After the brother opened the door, I found that my Ranger could target the chained dwarf from just outside the room. So I destroyed 3 of the 4 pillars, then knocked down the dwarf with arrows until he stayed down. Then I destroyed the last pillar and Mor appeared. But he had no line of sight to anyone so could not possess anybody. He just stood there while my Ranger hit him with arrows until he was dead.