Wait for Serinar to administer the disguise of a Burning Depths Necrolyte, then proceed to the back of the Maw of Neltharion to uncover what the Cult of the Damned is doing there. Return to Serinar with details regarding their purpose.
Uncover the Magmawyrm Resurrection Chamber
The Cult of the Damned has not come just to extract power from dead dragons. I suspect I know what they are up to, but I need you to prove me correct.
I will grant you the guise of this dead necrolyte. Proceed to the back of the cave and confirm their intentions for being in this sacred place. I will watch through your eyes.
Be cautious <name>, any damage done to you is likely to break the fragile illusion.