And so, just as I said, here comes a little bit more detailed battle description:
To introduce the my party here is a small list (unique abilities included):
1.: Sygius (PC Monk): lvl23, 108%
MR, -12
AC, -10
THAC0, 104
HP.
Special abilites: normal monk abilities, Shadowless Kick (1) -one-time attack, opponent falls uncounscious for 6 sec. and will be knocked back if the save vs. breath is failed ,Chant(1) Physical resistances are set to 60%, 10% bonus to elemental and magic resistances for 3 rounds,Dragon Fist(1) Removes Spell/Specific/Combat protections and lowers magic resistance - there is a different saving throw for each effect.
2.: Korgan: lvl.22. -13AC, -11THAC0, 174
HP
Special abilities: War Cry(1), Hardiness(1), Power Attack(1)
3.: Edwin: lvl.19 57HP
Special abilities: Dragon's Breath, Improved Alacricity
4.: Imoen: lvl.14 81HP
No special abilities
5.: Valen lvl.14-16 Fighter-Thief (Vampire) -7AC, -4/-4
THAC0 77HP
Special abilities: vampire immunitiesand abilities, level drain(2/hit), Whirlwind Attack(1), Assassination(1), Use any item
6.: Silver Star: lvl.24 Assassin 61
HP
Special abilities: Sulphurous Poison(1) -improved Poison Weapon, Dirty Fighting(1) -
ToB ability, for 2 rounds the thiefs attacks either slows(50%) or blinds(50%) the target for 24 sec. if the attack is succesful. The thiefs attack rolls and damage suffers a 5 points penalty.
Many of my characters use powerful euipment. Some of them are from the Tactics, or the Item Upgrade mods.
Tactics: (SPOILERS!)
My (winning) tactic against the Chosens was the following. First my monk used a Wand of Frost (damaging every opponent), Valen cast
PfMW, Korgan Cast Hardiness, Silver used Sulphurus Poison, Imoen and Edwin fled to the south immediately to avoid the attention of Bodak. The Chosens are going invisible, Selina uses her Spell trigger and sequencer (since no one had any protections, she dispelled nothing).
Bodak and Kerith appeared first, so I attacked Bodak and let Kerith cast Greater Command (it hasn't affected anyone). Bodak went down to Badly wounded, and used a potion to disappear. Since I hadn't had any party members to dispel their invisibility, they had a seious advantage by their constant disappearing/healing. I had 3 Remove Magic spells which did the job perfectly and dispelled the I.Invisibilities, but I've planned to use them later. Silver tried to attack every appearing opponent, but this time with little success, plus she was confused with Chaos and rushed forward... Edwin cast
PfMW, Imoen cast Stoneskin and she went forward in the heat of the battle. She was attacked by Grok immediately (his axes electrical damage hit through the Stoneskin). Venduris attacked my monk and did 90 damage, so I fled to the south to heal myself. Zaeron attacked Edwin, but because of the
PfMW, his attacks were useless. Edwin cast Timestop. During the Timestop he cast I.Alacricity, then a protective Spell Sequencer (Stoneskin, M.Image, Fireshield red), Dragon's Breath and Horrid Wilting (centered, so it will affect Zaeron, Bodak, and Grok as well), and a Greater Malison. Zaeron and Bodak always dies after this, and Grok goes down to injured/badly injured. Then I attack him with melee, but more often then not he manages to become invisible and flee to the north. Venduris works incredibly efficient, and kills Silver (destroying her completely

) backstabbed Valen, but missed. Selina stunned Edwin with Power Word: Stun. Grok attacked once again (Barely injured). Kerith attacked Korgan with Harm, and managed to hit him

-99%
HP, oooh yess.) So Korgan fled to the south to recover. The Monk and Valen attacked Selina after Imoen Breached her, and brought her to Near Death - she menaged to become invisible). Kerith was the next target (after all of them were made visible via RM) and he fell quickly. Every time Selina appeared she was immediately attacked by Valen or the Monk, so she had to concentrate on Stoneskins and potions of invisibility/healing and wasn't able to cast HW or such at all. A few rounds later she eventually fell. Grok attacked Edwin, and brought down his Stoneskin just in the same second he became controllable again - a quick
PfMW, and he escaped quick death. The rest of the party attaced the barbarian (Monk, Korgan, Valen), Imoen was waiting for Venduris to show up (to lower his resistances). After a long battle Grok died (huh, he IS STURDY after all!

) and there was only the boss left (who backstabbed soem of my party members during all this, and even managed to kill Valen). As I've said, his AI is fine and he is very elusive (not to mention that I ran out of RM

).. I used Korgan as a bait, and he survived the backstab (102
HP!). Allk characters attacked the assassin, bringing him to Badly Wounded before he drank his potion. After he fled behind the left gate, I summoned some monsters to block his way out (I know, not very fair, but hey! Neither is he

) He had to cut his way through Ogres and Hobgoblins, and each time he attacked I fired him with Malison, M.Acid Arrow, Magic Missiles, and attacked him with Korgans throwing axe and the monks melee (which has an attack range of 2, so I was able to hit him from behind the Ogres). He did his job so well, he managed to kill 3 Ogres and actually ESCAPE my blockade

to the south. He wasn't able to heal himself however, because Edwin was already waiting for him with a big bad HW. He died in battle, and with great honour

.
Comments, suggestions, ideas:
-I question the logic of the encounter in one point. If the cutscene takes "2 days" to lose all beneficial spells and effects, than I think it would be at least fair to let the party re-memorize the lost spells. You know, if someone plays the Improved Bodhi fight with Undead Solaufein included, he/she will lose almost every notable spells. Without these this encounter is a bit too hopeless, even for a high level party. So let the party memorize every lost spell before the encounter.
-Grok shouldn't attack mages only. This makes him very vulnerable to the
PfMW/concentrated fighter-attack combo. Maybe attack the Nearest creature(?) soemtimes. Bodak should attack a bit later, and he could take care of the spellcaters. Use the potions more often with him, since he falls very fast!
-Selina should cast more protection spells to avoid becoming vulnerable.
-Think about my suggestions on Kerith! I think he should either attack with Harm, or Flame Strike (or something similar). Use both spells and melee - always bringing him into the middle of the rage is very suicidal.
-Zaeron and Venduris are perfect, there is no need for a change.
Summary: this is an excellent battle, I really enjoyed it. It is beatable with a normal party, but offers much chellange to higher level parties, even with high-level abilities. I wouldn't offer to start this encounter before 2.900.000-3.000.000
XP, but it IS beatable with an
XP bellow that. Tha AIs now work properly - and some of them are extremely well written! - and the opponents use their equipment and abilities with great efficiency. Their teamwork is well balanced. Nice work aVENGER! If you need any other support, just give me a call, and I'll be happy to "work" with U once again!