I am going to hold off on posting until Lia and Geoffroy post. If they think Poljen should come face the devil, he will turn and run, despite any Attack of Opportunity. His ability to endure a fair bit of damage might make sense… but if they think he should try to help finish the duergar while those down there think they can handle the devil, he will stay put and keep mowing them down.
So… I am guessing the best bet here is use Geoffroy's channel ability?
More, use Radiance of the Dawn? Whereas with an action, he present his holy symbol, and any magical darkness within 30 feet of him is dispelled. Additionally, each hostile creature within 30 feet of him must make a Constitution saving throw. A creature takes radiant damage equal to 2d10 + his cleric level on a failed saving throw, and half as much damage on a successful one. A creature that has total cover from him is not affected.
Edited: Thomaslee on 5th Aug, 2017 - 3:15am