So, I'm at the end of Act 2 (I think), and I've been stumped for like 12 hours of game time. I need some help.

So im at the fight with Ketheric (where he becomes the apostle after you beat him), and I can't for the life of me do it. I'm at level 7, and playing on Tactician Difficulty, and my party is Tempest Cleric, Minthara, Lae'zel and Shadowheart. I can beat the first phase well enough, but once the apostle turns up, I get rekt every time.

My current strategy is to hide in Minthara's Darkness while DoT effects tick him down. I have Lae'zal respec'ed into warlock (for hunger of hadar), and Shadowheart speced into Druid (for heat metal) (yes I know about Wyl and Halsin, but due to some early story mishaps, they're dead).

Are there any ways I can do this? Or should I leave and Grind out a level?

Edit: This worked.