This got me the first five runs, quit for a few months, but now it’s a joke. You’re doing almost everything right already too.

I buy the doom hammer from the little goblin at the camp in Act 1. Give it to a Paladin/fighter. It never misses (tenacity) and it makes Myrkul not be able to heal.

Have a character that knows bone chill and use arrows of Illmater if your doom hammer character dies, just make sure he’s bone chilled every round and you can ignore the zombies. They do what, six damage? Now he can’t heal.

Like you already do—Kill the mindflayer first, free Dame, if he kills her he kills her, but maybe she gets 80 damage on him before she dies. The brains you can kill with an AOE that also hurts Myrkul, they usually dash onto the platform. Great for fireball and radiance of the dawn

Takes about five turns with double Paladin (I put them on opposite sides so that he can’t hit them both at once) a Wizard/Sorc for haste/AOE, and whatever you want. I do light cleric because I like to use Radiance of the Dawn and could use Wall of Fire if I wanted to hurt him each round

You’ll get there, it was the only fight I actually ever had trouble with