I was so worried that this fight was going to be like the hardest boss battle of all-time after reading the dozens of posts talking about failed attempts at it. Well, I wasn't about to replay the single-player again for a 5th time, so I decided to give it a shot.
Anywho, here's the gist of it. My character is a Level 34 Warrior (Guardian/Berserker/Reaver) and she has 141 Constitution with gear+bonuses. It's funny hearing about Warriors kiting anything in any game, but here's what I did.
After my entire party dropped in a matter of seconds, I knew this boss wasn't anything to fuck around with. So, I did lose a little confidence lol. But I just stuck to my original plan and it paid off. What I did was ran all the mobs around in circles continuously, casting Carapace whenever it was up. If my health was low, I'd take that time to chug a couple potions. I then ran up to the boss, cast Massacre and Peon's Plight on the boss and maybe a couple cheap melee hits until Carapace was 3/4 gone. After that, I ran for dear life and repeated the cycle until the first form of the boss was defeated.
For the second form I used the same technique, except instead of using Peon's Plight on the jumping form, I switched it out for the quad-hit shield technique. I only used this when the boss started healing itself. One quad-hit pretty much negates all of his healing effects. That and a cheap Massacre whenever I had the opportunit and it was a cake walk. And when all the skeletons disappeared for like the last 20% of his health, I just went all out, since the boss could barely hurt me.
All I can say is that was one hell of a boss fight. I wish the original game had some memorable fights like that D: I suppose the Brood Mother and High Dragon would be pretty decent fights on Hard, but I wasn't that brave.
All in all, my favorite non-Awakening DLC by a mile. Really glad I decided to download them all when they were half off.