91 Warrior fought this guy with cleric merc along side. It kept casting Balance of the Nameless about every three to four seconds. The spell description lists that it removes spell debuffs, but my experience is that it also restores their health. Lowest I could get it to was around 80% and bam BotN and it's back to 100%. I was hoping it would eventually run out of mana and I could kill it, but it didn't.
We just kept going back and forth. I'd never drop below 95% health (thx to cleric merc) and it'd so stay near 100% as well. I used the opportunity to top off all the various weapon skills that I'd been neglecting, even skilling up about 50 points in my Hand To Hand skill. Once all my skills were topped off, I just ran away and it deaggrod.
I don't know if this spell effect was added after all these other people said they solo'd him, but I can't see how that's possible, unless there's some way to block it that I'm unaware of or maybe someone can just do a whole lot more damage a lot more quicker than I can.