During an encounter with Yuvan Rokta in an ancient sepulchre, you may feel his hypnotic gaze at work in your mind. He is compelling you to hand over the ashes of the Eldest. If you choose to attack him, you may successfully remove his head from his body. You promptly douse his corpse in oil and set it ablaze. Once all of the skin has been removed and only bones remain, you claim the skull as proof to Commander Zalic that you were successful in defeating the Vampire.

Showing it later to Zalic he shares a dire warning.

“Their bones retain some of their essence, long after death. That skull can still hypnotize. Keep it safe, but do not point it at me again.” - Commander Zalic - Outbreak in Undercity (RPA-ADV3)