Praying a stormer doesn’t cast trough terrain.
Seriously, you need to go high stagger high dps. Bw conflag/slayer stagger ult/ fk/ shade or bh work. It will take a few tries tho depending
Hm, I haven’t done the challenge or even tried it on Cataclysm as I just play public games but I think I would use something like Ironbreaker with Shield, Witch Hunter, Mercenary and … hm … Shade probably. Looking for two concentration potions and using Decanter and/or Proxy.
I haven’t even attempted it on Cataclysm, but I imagine some Barkskin would actually be pretty good if you’re constantly taking damage.
Or are we talking about just clearing the event at all?
No, clearing works with any team composition. We talk about the challenge. That one actually needs some preparation.
Hm, I would like to have Handmaiden somewhere for Stamina but the other positions are more needed. And Shade is quite good at getting the Chaos Warriors. Although with three stagger ults the stamina regeneration might not be needed. Hard to say without actually trying.
In my mind the optimum crew would be Mercenary, Shade, Bright Witch, Slayer/Ironbreaker. I feel like it really rightly combines a bunch of damage mitigation (45%DR from the Mercenary shout is insane) and if you can get appropriate up-time on the Mercenary shout you’ll probably be fine???
Why not, I’ll give it a whirl tonight.
I just gave some examples, plenty work. Some better than others. Potion luck from the map also makes it easier, so saving pots makes it much easier aswell. Just expect to be overheaded a couple times 
It seems the end of convocation is still imposible
I used to hate this map, and then I understood you don’t have to stay up there, and now I love it. Easy as that.
It was literally the first map I completed in Cata… Impossible might be a stretch.