After killing him get his body loot and put it into the skeleton next to his spawn point. If the bones are not there you need to wait for them to re-pop. 15 up to 40 minutes, cant miss them. This will spawn Eldrig the Old (83^^^, Abilities: AoE Stun, Knockback and Mez). Kill him to get the axe.
Return to Morwynn.
A portal opens and mobs come pouring through. All are 82^^^ Heroic. Kill them until you get your update.
Protect the Apprentice! If the mobs get near here she will die with the first AoE they throw! If she dies you must start all over again.
The zone has no cooldown or lockout, so if things are going badly just zone out and return to try again.
Once you get your update the gate should close. Speak to Morwynn again to claim your weapon.
Inside you'll find a recipe next to the forge. Create your mythical weapon. The recipie looks like a scroll on the floor, and it's around level 2 or so for crafting.
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.