This morning, I defeated Improved Irenicus with my level 32 solo Sorcerer from the first try. First a couple of bugs (I was not using the latest version - ignore it if this is what you meant by DLG fix in the readme).
1) When Selfish dies, you do not get the Cloak of Mirroring back. It used to be on his corpse, but not anymore. I looked on the floor with TAB - nothing. Nor is it anywhere in my inventory.
2) When you face Slayer Irenicus, I get this error message:
Action Errors:- Warning: Too few parameters: CreateCreature("Shadow01", [1900.2100] Line Number:2
My general strategies for anyone interested: Use Project Image or else you will run out of spells fast. I summoned a couple of Planetars as cannon fodder, then ran away and cast Project Image -] Time Stop -] Improved Alacrity -] selected spells. The first Image killed Pride - 3x Lower Resistance, 6x Scull Trap and a couple of Magic Missiles. The second Image killed Greed with 6 Magic Missiles and then took care of the Beholders and the Lich (I assume they show up when you play on Insane). Fear was killed by the Planetars when I wasn't paying attention. Image Number 3 dealt with Selfish (Horrid Wiltings and Scull Traps). I lost a couple of Images in this process because of the dispelling and because Wrath managed to get a hit on me (60 HP with one blow - ouch!). Using another Image, I summoned some more Planetars - unfortunately, they seemed to be unable to hit Wrath except on a Critical. Still, they killed him in the end.
The slayer form was relatively easy - Time Stop -] Improved Alacrity -] 3x Horrid Wilting (+ whatever damage the Planetars that were left over from killing Wrath had done). My big mistake here was that I forgot to use Project image and had thus only 4 level 9 spells remaining. I managed to finally get Rest with Wish, but not before getting a Planetar mad by intoxicating him.
The final form was extremely frustrating - I had trouble chasing him down with a full party, now I only had a single character. First, I managed to run away for long enough to put on my Robe of Vecna again. Then, I tried summoning tons of Planetars - except they seem to be unable to hit him when using their swords (wound up using Fists instead). My spells appear to do absolutely nothing to him - both damaging spells and stuff like Breach. He also managed to get 80 damage on me with Cone of Cold (this wouldn't have happened if Selfish had given me the Cloak back - I thought I was immune to damage) so I had to run around drinking healing potions (only 95 HP to start with). He couldn't kill me - but there wasn't anything I could do to him either. The Planetars do not do enough damage with their fists and he teleports away and heals. Interesting note: there is a summoning restriction even PI doesn't ignore - you can only have 1 Wizard Eye at a time. I SO miss my moose.
In the end, I had the Planetars (by this time, I was using around 5 at a time) all cast Insect Plague on him. It didn't stop him from teleporting, but at least he didn't heal. Still, this failed once - the Insect Plagues ran out, he ran away and healed again. I got him the second time - around 10 Insect Plagues and 5 Planetar fists. The weird thing was that he refused to die - he just lay down on the ground (maybe sub-dual damage - but he was far from any Planetar at the time). I killed him myself with one blow of SotM - shouldn't he be immune to it?
Suggestion: can you make the final form a little less frustrating? He has a lot of infinities going for him.
1) Infinite and undisruptable teleport
2) Infinite healing
3) Infinite offensive spells (I don't mind this one)
4) Complete immunity to all spells except his own (I am not sure about this one, but it seems to be the case)
5) Weird weapon immunity - I thought it was Prot. from Magic Weapons, but then SotM killed him so...? :huh:
Can you make his teleport disruptable? Or somehow make it so that I don't spend an hour (literally - it took me an hour to hunt him down) running after him? It is not fun. This applies to the full party as well as to the solo character - unless you can stop him from healing, it take a long time to kill him (except if you use stuff like Arrows of Biting).
I think Improved Irenicus is very hard to Solo with some classes. For example, I do not see a way to do it with a Mage who doesn't use Project Image (a Necromancer) - you run out of spells. A Cleric - I am not sure; you will run out of spells and you are not good enough in melee due to lack of attacks/round. A Fighter probably could deal with the Sword of Greed somehow - Ring of the Ram, Ring of Energy; but then it would be hard for him to hunt down the final form of Irenicus - Arrows of Biting are the only thing I can think of. A bard or a thief - maybe if you lure them into Spike Traps - but I don't see you having much of a chance against the Fragments.