Just wanted to write a quick little help guide on this and what I found was most helpful.
First, I did not have the "required" legendary items for this. Ilvl was 926.
I had 18k nethershards saved up. I tried about 80 times a few months ago to no avail. I resubbed and within 3 days tried about another 80 times, but kept at it and did it. There's definitely a little luck you have to catch as well. knowing that one time the RNG Gods will be on your side with your persistence and effort.
As I first started doing the challenge, everything seemed SOOOO overwhelming, but like all things, you get familiar with it and the routine of Kruul's repeating eternity.
All those failures showed me when and where I messed up (sometimes it was not even my fault!). But pay attention to what kills you each time. I had to be very patient and not get too upset, even though I did at times want to destroy the universe around me *winks at Sargeras*.
At first, I could not get to phase 2.
But I kept at it, and started to make it to phase 2 about 25% of the time. then 50% and soon just about every time.
Phase 1 become easy, even though sometimes I would still get shot off.
Now phase 2 seemed an impossible feat. Sometimes I would die immediately and I would not not why.
As time went on it all started to make more sense.
Then with a little bit of faith and prayer, Kruul was gone forever!
So here are my tips as to how I dealt with this baddy
***But first I want to say what I think was the key factor in me completing this... ***Was Bear Tartar***.
This is a Food you can buy off AH for pretty cheap that gives you a movement speed buff for 5 seconds after you kill an enemy.
The movement speed from things dying around you as you spam your AoE abilities will save your life.
Talents:
Brambles
Wild Charge
Balance Affinity
Typhoon
Galactic Guardian
Guardian of Elune
Rend & Tear
Legends:
Oakheart's Puny Quods
Elize's Everlasting Encasement
Nothing too great, the 2 extra Thrashes probably helped, but I'm sure other Legends would have helped more, this was all I had though and highest Ilvl.
Phase 1:
So I started as a Moonkin from max distance, would cast Sunfire and Moonfire as I back pedaled to the edge to bring Variss to the center where Velen could Melee him as he does more damage that way. Then he would normally cast drain life as he got right to Velen so bear form> interrupt> Thrash> back out> spam Moonfire as you circle the radius of his BAD aura. Sometimes you will have to back up change rotation and so on. Anytime you end up running into the circle try and get Thrash on Variss. I would circle the radius of his aura spamming
As the eyes pop up try and Moonfire them dead. You get used to their timing.
As the Infernals start spawning you can cast a moonfire or 2 on them, but leave that to your AoE's as you are attacking Variss and the Nethers.
Keep you're main focus on Variss. ALWAYS interrupt Drain Life or all your efforts were for not. If you don't get it immediately that is okay, but more then 2 or 3 seconds 2 or 3 times will result in failure... :(
As you charge in to interrupt was when I would spam Thrash and maybe get a Mangle or Maul off on him. Then back out. Continuing to Moonfire.
When the purple gates come up you know Netherhorros are coming in about 4 seconds, so try and make it to where as you are circling you'll be near one as they spawn. You can hopefully Mangle & Maul one dead before they start moving. If I was not near one I would Moonfire to try and grab aggro. If you hit one before they start moving they will all charge you instead of Velen (sometimes....)
They will charge Velen and you don't want that. Shortly after they charge out they will START to cast Netherstorm I think it's called. Make sure you wait for the cast to go off before grabbing a life orb or casting Incapacitating Roar. I grabbed Typhoon here as an extra way to interrupt.
A neat trick for this I found was: if I took a bit of damage from the netherstorm before interrupting, I could Frenzied Regeneration for a nice bit of health back and not have to grab a life orb. But be careful, the damage is fast and hard.
So with luck and persistence you will start making it to Phase 2 :D It got to a point where I could have an orb or 2 up as Phase 2 began.
Phase 2:
WTF IS GOING ON!!
So he comes in on his high horse thinking he is the SH*T! .. which he apparently is for a while..
It seemed as if I'd never be able to complete this at first. Until I found the Bear Tartar.
The main reason is the Green puddles of ooze he drops after he casts Annihilate and jumps at you. They do a lot of damage and slow you.
I would be continuously jumping and kiting in a circle a little farther than halfway from the center and edge of the platform.
ALWAYS interrupt Twisted Reflection or it's GG.
Never stand still or you will get knocked off.
Try and keep Ironfur up.
Survival Instincts, Rage of the Sleeper, and Barkskin as each Annihilate comes (Not all at the same time).
Like I said, experience and a little bit of luck are what made this possible. So don't give up after failing 40 times, maybe take a break :D . Learn from all the things that kill you (or Velen). Never give up, Never surrender!
If you have more inquiries ask away, I'll help the best I can.
GL~!
~SpaceChrist