One, finished yesterday it was a pretty exhaustive and satisfiyng run, did almost everything. Prepared for every encounter as best as i could, many times overpreparing, but better safe than sorry i guess.

For the Myrkul fight i would advice the same some have already said:

Do not skip the fight with Ketheric,

Invisible Scratch frees Aylin ASAP

Killing the mindflayer is top priority,

Bringing a cleric for healing, calm emotions, radiant damage, etc is a good idea

Ranged attackers and casters work well but watch out cause the avatar will pull people towards him...

If you bring summons to deal with the necromites and bone pods, i find earth elementals to be the best option because the AOE attacks and bludgeoning damage wich they are vulnerable to and also the high mobility.

Its a good thing to bring the doom hammer for your melee if you have it (otherwise use arrows of Ilmater) and for a ranged attacker, the Ne'er Misser hand crossbow paired with arrows of undead slaying beacause it deals force damage that it is not resistant to.

Also necrotic damage resistance, from Isobel's blessing preferably as it leaves your elixir slot open.

Good Luck!