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From Pathfinder Wake the Dead #5, which isn't enabled.

Nyctessa's Staff

ITEM 4
UNIQUEMAGICALMONKSTAFFTWO-HAND-D8
Price 90 gp
Usage held in 1 hand
Bulk 1
Category simple
Group club
Damage 1d4 bludgeoning

This macabre staff is crafted from gleaming white bone, a spinal column spiraling out of its base with a skull swinging from the spine's tip. It was handcrafted for Nyctessa by her father, a powerful Blood Lord, from her mortal mother's bones.

When you damage a creature with Nyctessa's staff, that creature gains weakness 2 to void damage until the end of your next turn.

Effect: Sepulchral Drain

Activate Cast a Spell
Effect You expend a number of charges from the staff to cast a spell from its list.
Pathfinder Wake the Dead #5OGL