Halloween 2008 Quest. It is used to destroy the Skull Totems that have appeared in graveyards throughout Britannia. One can be aqcuired through completion of the quest after killing Sicarii. One can also sometimes be looted from her corpse. Take the venom sac to a totem and use it. It will tell you that the Skull Totem has been damaged somewhat. It is unknown how many are needed to destroy one.