The Dark Eldar use captured wraithbone looted from the bodies of slain Eldar Wraithguard to create a special kind of ammunition that they use in battle. Models using soul seeker ammunition may re-roll any missed to hit rolls, and any cover saves that would normally be taken by the target are ignored. Soul seeker ammunition may only be used in conjunction with a splinter rifle, splinter pistol, tormentor helm or a hellglaive.
Soul Seeker Ammunition
Source: Codex: Dark Eldar (1998), p. 15