Go to the Master's Terrace in Karazhan and use Kalynna's Urn to summon Nightbane. Retrieve the Faint Arcane Essence from Nightbane's corpse and bring it to Archmage Alturus.
Our preparations are complete. I have put the materials you gathered into this urn. Take it to the Master's Terrace, where the fight took place, and set it on fire.
The energy released will bring life back to the charred remains of Arcanagos. Defeat the creature and retrieve its essence immediately! You will need to take it to Alturus.
Should you fail, the stars predict you will have let a great terror loose upon the skies.
A terror known as Nightbane!