901, 41-trait Prot Warrior here. I pulled this 50 times tonight and still have yet to beat it. I went in totally blind (didn't wait for any information to come out before I pulled) and it took me about 20 pulls to start to get a feel for the mechanics. Here's the build/legendaries/trinkets I used, and my tactics:
Talents:
This build provides the best tools for stopping or mitigating Variss' casts while allowing me the greatest amount of CD reduction and self-healing from legendary bracers (Vengeance affects AM and bracers based on the full, unbuffed amount of rage consumed, not the reduced amount). I was able to have BC and Demo Shout up very often, which I'll talk a bit about later.
Legendaries: bracers/gloves
Trinkets: 885 Skorp stam trinket, 880 Parjesh's Medallion
Statline: 15% crit, 23% haste, 13% vers, 31% mast, one piece of gear with speed on it. 6M hp with flask. No food buff.
My normal statline has more haste and mastery, but I swapped some pieces out for vers to help mitigate Variss' Mind Rend ability, which would hit me for about 2M without the help of any debuffs from the adds.
My strategy involved charging in, popping BC and building up the biggest IP I could while doing as much burst as I could before accruing too many -%hp stacks (I would run out after my max hp hit ~4M).
Since I have the new 1/1 trait for 20% more reduction on spell reflection, I was able to deal with the Mind Rend decently if I had something to generate rage against.