Wraith

The Death Family, and specifically Charon, is at the top of the list of families that the Watchers wants destroyed because Charon had a hand in helping to destroy the first Council. Until now she assumed they'd killed all the slayers but another faction was formed at the time to deal with the Council should they return in any way shape or form - Wraith.

Wraith has become legendary because no one ever see's their operatives and when they do their faces and even their eyes are covered to prevent anyone seeing who they are. Wraith operates in crews, the most elite crew is Skeleton which has four operatives and is the Councils primary target, find and kill the members of Skeleton Crew.

All members of the council are aware of Wraith but have never been able to get anyone on the inside.