The material below is Open Game Content from a 3PP Source
Aura strong transmutation; CL 15th
Slot none; Price 12,780 gp; Weight 10 lbs.
This +1/+1 two-bladed sword has blades of alchemical silver. The weapon deals an extra 2d6 points of damage against any creature with the shapechanger subtype. When a shapechanger or a creature in an alternate form (such as a druid using wild shape) is struck by the weapon, it must make a DC 15 Will save or return to its natural form.
Requirements Craft Magic Arms and Armor, baleful polymorph; Cost 6,780 gp