Maybe somebody who has finished the game with Tactics4IWD2 installed could help me with this.

After many days and even more reloads my party:

-Aas Pala1/ Painbearer 15
-Drow F4/Barb3/ Demarch9
-Strongheart Ro1/Monk16
-Human Monk1/Druid 16
-Tiefling Ro1/Mage16
-Human Ro2/Barb1/M1/Bard13

is about to do the Ritual but Iyachtu Xvim is a tough cooky. My strategy so far has been:
1. buff up everybody to the max
2. let the monk initiate the ritual and then engage Iyachtu.
3. surround him with fire elementals and get rid of the Cornugons and Glabrezu
4. then there is my party + elementals against Iyachtu and I can hardly scratch him

The fight is even for a while ( read even as in nobody hits anybody ) but sooner or later the
cleric runs out of Holy Auras and that's when thing start to go down hill. I have tried Lower
Resistance x3 and everything to bring down his saving throws but any attempt to catch him wih a
Feeblemind/ Hold Monster/ Powerword Stun or similar stuff seems to be futile.
My fighters tried +5 weapons, brilliant weapons, 2H weapons - but nothing seems to get through.

Every now and then Iyachtu may take a bit of damage from a Static Discharge but not nearly enough to call it progress.

This party may not qualify for an UPP but it prevailed against the Lost Followers and Chahopek so there must be a way - any way.

So please, if you have finished that fight tell me about your strtegies and if it contains a
spoiler then, by all means, feel free to spoil away.

Oh, and given that the lead character is a Pala/Painbearer siding with Iyachtu just isn't an
option ;)

1> Easy way:
After you have slain all the minions, use a protection from magic scroll on the boss. Then he will summon 2 liches. Use Disintegrate to quickly destroy the liches. Then you can easily take down the boss.

2> Not easy way:
All melee PCs use power attack, your mage could use Mordenkainen's Sword. Executor's eye will grants you impressive criticals. Champion's strength and improved haste will also help you a lot. He is immune to most disabling spells, so don't try to disable him. If your melee PCs don't have blind fight feat, you'd better cast see invisibility a lot to help yourself. Sometimes he may be unaffected by see invisibility because he has Minor Globe of Invulnerability on.

I don't know if Tactic4IWD2 just tosses the difficulty up a bit but considering I have a Aas Paladin as well(and I'm not a powergaming punk....I have a low tolerance for people that put ONE level in anything....). I had no trouble with him at all, just buff yourself with clericness and have at him. I had my paladin hold him off as the rest of the party cleared out the demon summons. Sure I had the cleric Healing him every once in a while, though I did complete the Battle Square so I don't know if that could make a difference.

i've tried everything. i have a 1d10+2,+2,+2 battleaxe, a 1d10+2,+2,+2 war hammer, a 1d12+1,+1,+1 battleaxe, a 2d6+4,+4,+4 great sword, a 1d8+4,4,+4 mace and enough magic to sink a battleship. i might as well just stand there and do nothing. the best i have been able to get him to is badly wounded. WHAT WORKS??:mad:

Let him chase a speedy character who stays just out of reach and attack him from a distance with the cloudkiss axe. He is vulnerable to electrical damage and will take an additional 5 points of damage with every hit.

yeah except you only hit him with the cloudkiss like once every 86 times and no matter who he attacks he hits every time for massive points:o i give up

Hey, you're in good company -- I gave up at that point too. :p

rmftsill, you could turn down the difficulty in the gameplay options, if only for that one particular battle...it would be a shame to give up so far into the game.

i already have it all the way down:o

rmftsill, do you have a paladin that is actually good at fighting in your party(with blind fight feat)?

no. i have a barbarian and a fighter. both half orcs. blind fight is n't necessary that i see. it can't be done.:bang:

In fact Blind Fight feat becomes very handy at later stage. I think, as I played the game with this mod, that a fighting Paladin is necessary for, almost, completing the game. I can imagine your barbarian and fighter not doing enough dmgs...sigh, this mod is for powergaming, characters that work fine enough in normal mode aren't good enough here.
In my game I used the Fighter/Paladin chara to tank the Xvin and others(mainly summons) take out other mobs. I can't remember the details, but I thought fire resistance was quite important against Xvim?
Sigh im sorry i can't be much of a help. You just better be prepared to cast see invisibility like crazy if you don't have blind fight. In my case most dmg done to Xvim was from Holy Avenger(dmg against evil+blind fight feat). And obviously you must take out other mobs first before whacking Xvim. If my memory serves, he isn't the last thing you would be killing in this battle with this mod installed...good luck!!

Please have a look at the new version Tactics4IWD2 V2.0 (http://www.sorcerers.net/forums/showthread.php?t=45453).

Some bosses have been slightly weakened, including this one.
You could uninstall the old version and install the new version, and have a try.
However, you still need A SAVE BEFORE YOUR FIRST ENTERING THE CLERIC TOWER.

And good luck to you. ;)