(Spoilers below)
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OK, I've got the dagger from the demonknight in Durlag's Tower (whopped 'im all by meself, without resorting to the mirror :D ), went back to Ulgoth's Beard, had the said dagger stolen from me and a heck of a fight with the cultists.
Now I'm tryign to finish Hurgan's quest & retrive the dagger, but the $#&@%#&@ demon is tough!

Any general tips on what works, and what doesn't in this final fight?

BTW, those cultists by the side - they stay immobile. What's up with *them*?

Never mind - I read a few months' worth of posts and fund the answer here.

[img]smile.gif[/img]

did you bust out the sphere?

The Forum Archives are a treasure trove of wisdom - be sure to check out the search facility.

It took me a few attempts to find Aec-Letec's weakness but after that it was so easy. My solo Fighter/Mage got him without ever being seen! And his weakness is -
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CLOUDKILL.

I promised myself that next time I'll do it the hard way and get up close with him.

Well, after about five or six attempts I dusted the Aec'Letec while keeping my party alive (previous attempts had one or more party members dead, some to the point of being "chunkified" or turned into ghasts). The difficult part was his spells, especially the one which holds party members.
Dispel magic was really useful here, to dispel the hold and the "dying" (the one that eventually turns an NPC into a ghast).
I also used many area effect spells to try to kill the cultists and quickly as possible - cloudkill, fireball, necklace of missiles, arrows of detonation. Plus summoned monsters/animated dead to keep Aec'Letec busy whilst I tried to kill all the cultists. Haste & oils of speed helped a lot too.

Hayashi, it's good that you beat the Aec'letec, dude but I've got to say that was a messy fight you had with him. With a bit of subtlety it is possible to avoid a lot of the frantic 'Dispel Magic' type problems. I charmed one of the Cultist and used him to lure the Big Guy into a corner of the room, this allowed me all the time I needed to get rid of the rest of the Cultists without being attacked. Finally, when I was ready, I moved in for the kill.
From start to finish I was able to dictate how the battle developed, which I guess is what a good general wants to do.

Midget Gems - we may be small but we're so SMART!

I suppose you're right but the battle kicked off almost as soon as the level loaded, after talking to the cultist.
But then I never tried charming on of the cultists ;) [img]graemlins/doh.gif[/img]
Anyway, the quest is done, I got Hurgan's reward & I'm now somewhere in the Trackless Sea tryign to retrieve a cloak for Shandalar.