Having suffered multiple deaths at his hand, the Dura'ek sentries can probably be killed solo by an uber paladin if he pulls it out of the pillars. They are quite weak when the turn smaller.
Hmm: Halberdiers are very tough and I doubt anyone can solo one at all. There is no way that anyone beat one of the Dura'ek Sentries solo. As far as Dura'ek himself goes, I've never fought him...