What's with the battle with Kerghan? [SPOILER]

[Mad]

I play an evil character, I spoke to Kerghan and decided to kill him. Battle begins, he turns into a monster, I "kill" him...... and nothing, he shrinks back to human form, can't talk to him or do any additional damage. starts regenerating to about half health at which point he attacks again.
I "kill" him again and again 3 more times at which point I exhausted all of my supplies.

What's the catch?

[Muro]

It's a regenerative shell, penetrable by only two known items. One is the Vendigroth device, while the other can be found in the Void itself.

It's Kryggird's Falchion, located in a cave in one of the void "islands", with the entrance marked with a "2" here - http://mikesrpgcenter.com/arcanum/maps/void06.gif

[Mad]

Many thanks! I went with the Kryggird's Falchion solution, since I gave Vendigroth Device to that Dark Elf guy.