Dartain will ask to duel. He's a Heroic 85^^ Necromancer with a T8 tank pet. You only need to hurt him to 10%. Sic your tank pet on his pet and set the aggro, then target him and launch all 5 of your dumbfire and swarm pets. Then make use of your Tainted Heals to keep your pet up. You cannot target his pet or your Tainted Heals will not work! When he reaches 0% he will respawn as an NPC again. Hail him to complete this step.
Return to Steelbone Family Crypt and click on the brazier outside the door to summon Qurst.
Kill Qurst. 85^^^ with 2 85^ pets - Kill his pet. Pet hits like a truck - need well-geared full group for this step. Necro's pets seem unusable for this fight - but swarms work fine.
Talk to Dartain again to perform the ritual and complete the quest.
Level 90 Mythical Conversion
Your Mythical Weapon has unique effects which will not work on level 81-90 spells, combat arts, or pets. By completing two quests, you may convert your Fabled or Mythical Epic Weapon into an Enervated Weapon and add persistent Mythical Effect spells to your knowledge book. This allows you to acquire other weapons without losing class-defining Mythical effects.
The quest requires that your class and your Epic weapon match. You will only receive the mythical spell gem of your current class.
You can start this series as long as you have the fabled version of your epic. But if you have completed "Epic Repercussions" then you will not be rewarded the mythical weapon if you go back and complete your class specific Kunark mythical quest.
The quests which make your Epic Weapon effect into a spell is the same for all classes.
The Necro Epic involves gathering the remains of Vazaelle Kaelyne, the Demi-Goddess of Insanity. She was all but destroyed during the planar invasions.
The remains of Vazaelle that necros have to gather is whats left of her mortal form when she was made into a demigod by Cazic. it has nothing to do with the invasion of the plains.
Although Vazaelle's soul was kinda ripped up as well at some point so the invasion might have done that, but never actually explains how it happened in the quest. just get sent out to gather 4 essence gems to put it back together.