I killed him eventually, after trying a lot of different strats, but it took about eight hours of attempts and over 200g worth of repairs The mechanics behind the fight are just ridiculous. I don't understand how they can design a boss that makes it impossible to cast heals, then give him the ability to pull everyone in and give them a DoT that ticks for more than half their HP.

The way I did it in the end was to position my shammies at the top of his stairs, facing down. Then I'd pull him around them, and move him in steps down the entire length of the bridge. Whenever he used a beacon, I'd mash the forward movement key on my shammies while at the same time backing up myself. Whenever he pulled my shammies in, I'd back up myself as well. I found that was the only way to keep him from applying the DoT to my shammies. Even then, it took all my cooldowns and a little bit of luck. At least I can say I killed him at the right level, and never go back until I'm 70.