Are beings like this guy:
Hard to see him, I know, but he's like Insta-Death Man. I threw about 7 characters at him today. By the time I got to my Warlock, and was killed killed killed as soon as I was back to life, and I was swearing like I do...it occurred to me just how bad it would be for me to be heard by others during fights like this. Tsk.
My Paladin (lvl 108) and my Demon Hunter (who I've let flounder at lvl 104) acquitted themselves well against him. The Demon Hunter actually got more hits in than any other character. I'll have to move her forward.
I have to say these bosses are different than any I've encountered in dungeons. I want to say Real Suckers, but of course I'm too polite.