Must be a Mage.
Kill Murlocs of the Silting Shore to summon a Quel'dorei Magewraith, then destroy it. Afterwards, speak with Bati at the Vault of Lights in the Exodar.
Quest Text Edit
You have chosen the path of the mage, and so you must learn control. Magic, when unchecked, can corrupt souls and destroy worlds.
To fully understand, you must face one who has been consumed by magic. Travel to the beaches on the northwest coast of Azuremyst Isle and use your spells to decimate the murlocs. The display of power will attract the attention of the evil force lurking there, a Quel'dorei magewraith. Defeat it.
When you have finished, seek out Bati at the Vault of Lights in the Exodar.
Just kill the Murlocs of Silting Shore until Quel'dorei Magewraith spawns then kill her.
You will be allowed to choose one of the following:
With every spell you must steel yourself against its seductive lure, using it only as needed for the purposes of good. Hopefully the wraith granted a glimpse of what you might turn into should you become careless--a mindless slave to magic.
Even if you've killed Quel'dorei already, it may respawn if you continue to kill more Murlocs.