I wanted to try the fight where you open all three seals to Demogorgon's area at the same time. There was a thread regarding this - it's on page 4 right now called "Most Difficult Scrap". I am playing on Core rules right now (i'm going to have to join the insane club soon, but i'm not ready yet). I have my evil party with Korgan and Sarevok, Haer dalis, Viconia and Edwin. (PC fighter/thief) My people have about 5 million exp each except for Sarevok who is way behind but makes up for it with the Dragon's Breath halberd and his charming personality.
Anyway, I took this group through Watchers Keep without resting, but i didn't use up too many resources so i would be set for this fight. It took me 4 trys to win it. It is definitely a fun fight. You have the six, that lich azamantes, four flaming skulls, and those "Rilman" fighter/mages - what the h... are those things, anyway?
My tactics: I tried some different summons, had pretty good luck with the fire elementals because there are a lot of incendiary clouds and scorchers flying around. I had Viconia do a couple of greater restorations - those are the best in the big TOB fights
Anyway, i definitely recommend this battle to anyone out there, If anyone else has done it post your results