I talked Ketheric into killing himself so it went right into the second phase. Then wizard misty stepped up to the mindflayer and used thunderwave to push him down to the ground below. Melee (Jaheira respecced as a paladin and Astarion as a fighter/rogue) took care of him quick, I don't think he even got to do anything. A combo of sunbeam (from shadowheart using blood of lathander) and fireball took out the little brains.
After that, I think I had Jaheira make a beeline for nightsong while astarion and shadowheart kept Myrkul distracted. With my wizard I also plopped down a fire wall on top of Myrkul and summoned a fire elemental. From there it was pretty simple: Nightsong and Jaheira spammed smites on Myrkul, Shadowheart healed when necessary, and astarion and the fire elemental cleaned up the necromites and their spawners. My wizard either launched fireballs to help astarion and his elemental, or just cantripped for some more damage on the boss. I got the achievement for killing him before he absorbed any of the little undead guys, so I don't know what that would do. The platform that the mindflayer starts on is good for casters or ranged damage dealers, my caster was up there and had free reign pretty much the entire fight. I think Myrkul might have once used a weird pull move that teleported my wizard right next to him, but I just misty stepped back up there. It lets you hit most of the battlefield with whatever spells you want. Scrolls of misty step would probably be useful for everyone in the fight since I think myrkul has a "no heal" aura that affects anyone that stands near him. Misty step would let people get to safety, and would also let other characters teleport around the battlefield when they need to take care of adds on the platforms and everything.
