Because I couldn't find video's or info for this quest concerning affliction, maybe the tips below will help others trying:
Don't bother with trying to kill the blob adds that Wrathion spawns. I couldn't kill them fast enough thru lack of proper aoe. Killing them one by one didn't help cause by the time the last one died, the first one already respawned.
Instead focus on the boss the whole time! That way you should get him down before he goes into clone phase.
Don't bother using a pet to tank the blobs, they will devour it in a matter of seconds anyway.
- buy 'celestial offering' from the august celestial quartermaster if you can, it will make sure you get an extra 10% intel buff whenever you are near the temple of the jade serpent
- food buff, intel flask
- Use grimoire of sacrifice; you don't need your pet anyway and the extra dps from sacrifice will help
- glyph curse of exhaustion so you can aoe slow the blobs bigtime
- take shadowfury as a talent, so you can stun the blobs
- set up portals from one end of the room to the other before the encounter
- I glyphed Dark soul as well cause I figured I would spend more time damaging the boss outside it's cooldown then in it
Always remember that standing right behind the boss will make you do 3 times more damage. Even when it seems you are standing in his aoe effect that way, you will take no damage from it!
So when the encounter starts, stand ready behind boss, pre-pot, pop cooldown, summon doomguard and blast away on him as much as you can. He'll do about 3 aoe attacks before summoning blob adds, make sure you get behind him every time to do as much damage as you can.
As soon as the blob adds are starting to get close to you, soulburn:curse of exhaustion one of them so they are all slowed and go back to dps'ing the boss. When the adds start to catch up again, alternate with aoe slowing them, stunning them with shadowfury or using your gateways to get away from them.
All the while try to damage the boss as much as possible, try to get behind him as often as you can, all the while avoiding the aoe effects on the floor.
This way I finally managed to get him down before starting the clone phase.
Demonology and destruction will have it easier I think, cause they can just aoe the blob adds down rather fast.
There might be better, easier or more elegant solutions, but I had a hard time with Wrathion, and this was what finally worked for me and I hope it'll help someone else. :)
I also encountered following problems (bugs?) in the challenge: