Rephallim

Ereth Khial's most feared servants are the Rephallim -- invisible wraith-creatures who lead souls to the Underworld and keep them imprisoned there. Worshippers of Ereth Khial hide themselves amongst Ulthuan society. They perform vile ceremonies entreating their goddess to send the wicked Rephallim to snatch away important High Elf counsellors, military leaders and mages. They summon the avatars of Ereth Khial with dark rites and set them upon their foes using talismans unique to each victim -- effigies made using the target's hair or blood, or treasured items stolen from the prey's home.

Source

 * : Warhammer Armies: Dark Elves (7th Edition)
 * : pg. 46