My solo party is 1 fighter-thief and 2 fighter-mages, circa lvl 24. I play at Heart of Fury.

Mostly my tactics involve summons and lots of AOE, so imagine my reaction when the final boss (and minions!) was revealed immune to magic. I stared at the window for minutes, mumbling how life hadn't been kind to me.

In the end I equiipped everyone with hammers and after a humble 5 tenser transformations each (to refill health), the boss went down. But no preparation time? Traps dispelling my buff? This game hated me.

The end boss is not immune to magic, he just has high magic (and elemental) resistance, evasion and very good saving throws.
Did you really expect that you can win the endfight at the hardest level on the first attempt with an unbalanced small party without priest spells just by repeating your standard tactics? ;-)

I remember that I planned using the water elemental shapeshift to get over 100 percent damage resistance for my HoF solo fighter/druid and getting healed by enemy hits, it was shocking to realize that the endboss was able to ignore the damage resistance. The other tactic I had prepared didn't work either, so I had to do something different.
But In the end it feels more rewarding if you had to put some mental effort into the battles instead of just repeating your standard tactics everytime. :-)

PS: Where did you get all the hammers +3 ?

It took about 20 tries lol. My weapons of choice were: Hammer of Conlan, Hammer of Life Giving, Hammer of Giant Sleep.

I'd forgotten about the little Dispel feature. I had a three-member party. Ended up using a few potions of invis, which gave me enough time to buff my crew with other potions (speed, strength-buffers, a few others). Then took him on. It was close, but we finally took him down just when I thought we weren't going to survive it.

Was restricting your characters to use only hammers a roleplaying choice ? Bashing is fun, but other weapons like longswords of action +4 would have been far more effective.

Did you finish both expansions before the final battle ? How many XP exactly did you have when starting the final battle (level 24 can be 5,624,999 XP for a mage or 3,080,000 for a thief) ?

I used the hammers because I thought the iron golems were immune to other weapons. At final boss my toons had about 4'500'000 xp, but with them I also play multiplayer online with friends (so some XP comes from there too).

I just finished the final battle.

I found out that you don't have to fight the iron golems.
Your party can talk with them.
If you speakt to one golem, than he will stand still for several rounds. One he starts to walk toward you magicans or clerics, simply talk to each one of them again.
This way your weaker characters still can do a job, and your spells can be cast when needed.

This, a strong weapoin (+4 / +5) and a haste spell made it possible to kill the demon.

These stories are cool to read! I remember the final battle, and it was just awesome.

This is called a Fake Talk, and works as long as the creature is neutral.

As for weapons, if you've been through HoW you should have purchased the mace Three White Doves. If you're lucky the magic of the weapon will deal nicely with Poquelin/Belhifet. My paladin had the Girdle of Stromos, an Oil of Speed and the mace ... and got lucky.