Doomfire Warlocks

When Malekith first learned of the Prophecy of Demise, his initial wrathful blow fell against the Doomfire Warlocks of Hag Graef. Fearing that they would rebel, the Witch King cursed them with hollowness, and their souls have teetered between the mortal world and the Realm of Chaos ever since. Thus, whilst other Elves fear Slaanesh as a potential fate, Doomfire Warlocks feel the Dark Prince's grasp on their souls grow with every passing day. As the grip tightens, dark runes blaze into life on their flesh, an unholy fire that creeps slowly across the skin. If this process is not arrested before the Warlock's entire body is swathed in flame, his soul is snuffed out and consumed by the Dark Prince. This fate cannot be thwarted, for no mortal can long deny rapacious Slaanesh. It can, however, be stalled if the Warlock sacrifices others in his stead -- the purer or mightier the soul, the better. 1a

Doomfire Warlocks descend upon villages in the dead of night, seeking victims to slake Slaanesh's thirst. Cloaked in shadow, they pass like phantoms through defences, stealing prey from their beds before vanishing into the night. When a Dark Elf army musters, the Warlocks gather, hoping to capture mighty warriors to fuel their rites. To aid this cause, they infuse their scimitars with numbing curses that strip a foe of his sense with a single scratch. Alive but mindless, the victims are led from the battlefield to the rituals that will keep Slaanesh at bay for a few days more. 1a

Source

 * Warhammer Armies: Dark Elves (8th Edition) -- pg. 41