Use call lightning and static charge!!!!
He's not immune to electricity and these two spells are not affected by magic resistance.
In fact you can kill him using
only these spells if you have enough of them (around 10). Start casting them
before summoning him. They will apparently be wasted but
the spell repeats itself after 10 rounds. So after casting all of them summon him. The spells should be repeating by now. Now all you have to do is try and survive while your cleric/ranger/druid (the one who cast the spell) is near enough him.
Try this thread
http://www.ironworksforum.com/ubb/cg...;f=23;t=001118