Is he weak to an element? Tried to use Dark with the Blades of Sin and Misdeed you get from the boss in the same place but I just noticed how my damage gets cut in more than half after a couple of turns, except my Attacker familiar's Surge attack, then tried equippign a mirage to get Surge damage but didn't notice a lot of difference.
I'll try the Star Warding charm, didn't know he could be stunned, thought he had immunity against that, I also thought about using the Aromatherapy weapon I got from Mirage (I have 7 right eyes but not a single Left or Middle, c'mon...) and have two AoE healers while waiting for Surge of Night but that might make the battle last an hour or so.
EDIT: Okay, outside of using Light attacks and Dark resistance equipment, any tips against the boos after, Versa? Haven't really gotten to her yet but I know I have to fight her