This quest starts by speaking to Sinephobis at the very back of the temples on the Fear Tainted Isle in Tenebrous Tangle (take the cloud transport station found at the upper West side of the Temple Grounds island in Tenebrous Tangle - on the way to the Sanctum of the Scaleborn). When speaking to him, be subservient and give proper respect to the Priest of Fear. Do not try to bribe him.
To save time, pick up a (1) scintillating incense prior to starting the quest.
Harvest five dragon bone parts in The Bonemire which can only be seen if you are on this step of the quest. They spawn somewhere in the area of these locations and have a short (1-3 minute) respawn timer. A Gnomish Divining Rod can be used to save time in finding the nodes for this step (a pile of dragon bones). You can also use the tracker for harvestable items if you are over 90 in tradeskill and got it from tradeskill prestige AA.
Return to Sinephobis and he will give you a recipe. He asks you to gather a few uncommon T7 harvests from any T7 zone (including Loping Plains). You can harvest them or buy them off the broker. If you already have the items, you can place them in a harvest depot or sales display and remove them for the update. You can also have someone give you the items or have them traded back to you. The items you need are:
blue-silver sheet from ore nodes (Kingdom of Sky zones: "firmament stone;" Loping Plains: "protruding vein")
perfect osseous lumber from wood nodes (Kingdom of Sky zones: "twisted wood" - found in Tenebrous Breeding Grounds; Loping Plains: "slate lumber")
You can use the Commission System for this step. If you use the Commission System for this be sure the person you are commissioning for uses their Instructions otherwise it will take your instructions.
Best to mentor to 65, lest Do'ellin gets stuck at 1%.
Send a pet to start (and potentially finish) engagement.
Can respawn in about 15minutes.
For multiple group members needing soul, be quick, as <Subdued> will despawn <60seconds.
When Do'ellin gets down to about 10% health, he will break the encounter and appear as an NPC, Do'ellin (with '<Subdued>' under his name).
Target the subdued Do'ellin and use the an ornate phylactery to steal his soul. If you accidentally aggro the Subdued version, or he is up when you get there, killing him will cause Do'ellin the Young to spawn again.
Return to Sinephobis. He will hand you three rods and give you six minutes to place them around the islands in the zone.
You will need to find "a spot on the isle, away from any mobs, to use the rod". Many people experience issues with this step, which is often the most time consuming one. See Placing the Rods on the talk page for discussions on tricks people have tried to get this near-bugged portion of the quest to work.
This will start a ring event animation with casters named a priest of fear. At the end of the event, all of the casters will be killed. After this event completes you can kill Do'ellin for the update. If you kill Do'ellin before the event has finished you must wait 30 minutes for respawn.
The ghost dragon is considered a massive undercon with a nasty AOE knockback.
To avoid flying into the air by the knockback, get yourself positioned into a corner, where the temple stones and the mountain wall meet together just behind the dragon.