I tried it without a guide and thats how I did it:
- first try I tried to lure him into the center and use the hammer, it took a long time and I found it complicated. Then several fire mephit adds showed up and I reloaded.
- Second try: 3 strong characters with hammers where he comes out, one caster at the lava valve. The hammer guys drink a haste potion and attack, the caster used magic missle when not using the valve.
Went down in 2 rounds without problems, even when only one of my chars used a haste potion (forgot it for the others somehow)

Prof. Dr. Dr. Mad S. Tist

World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already