Tank with your back to the stump located on his peninsula.
He has a melee AoE that has to be jousted, Piercing Darkness.
He has an AoE knockback, so control your flight by holding forward while airborne.
You'll have to cure Noxious.
There are arcane/traumatic poxules that have to be killed by mages/priests and fighters/scouts (if the wrong class hits it first, you're SOL)
If the poxules are up too long, they cast an AoE stun on the classes that are not able to kill them, so make sure you kill them quickly.
Battle Weary (raid-wide debuff) sets in after 6:30.
Combat Fatigue, the second stage of Battle Weary sets in a couple mins later. You probably wont live through Battle Weary, though, and you WILL die to the next Piercing Darkness melee AoE once Combat Fatigue has been applied.
Avatar has Consume Soul, so stay out of range of his melee AoE because it'll heal him.