Dragonwrath, Tarecgosa's Rest Scenario

I'm seeing tons of threads and comments about people completing this scenario, please could someone teach me how to kill this boss at the end as an 85 priest? It's seemingly impossible :/

https://worldofwarcraft.com/en-gb/character/silvermoon/cátloaf

Pri is by far the hardest of the classes atm. Shaman is probs easiest
Dot him, dispell heal, when mob come dot and mc and insta interupt. Then drop MC and kill it then continue same way

Talent for the MC where you dont control the mob. You have to spam heal urself and he will die from dots, use shadowfiend on the add to get rid of it asap. You get mana back at 15% so dont worry about it.
2/2/2/2/1 talents. You pretty much spam heal yourself and dps him when you use defensives. Kill adds as they spawn and use MC'd adds to interrupt boss.
It took me a couple hours to get the strat down. Make sure you have all the consumables and BiS gear/gems/enchants.

Update: Managed to get a kill, thank you guys ^^
I used your build @sti so thank you

Kill:

Gratz man!
Didn't know that healer fights were THIS long
As a mage, you get max 4 phases if you get timing on spellsteal right. Kill or be killed

Gratz on the kill, its hard for priests