SRD:Shifter's Sorrow

Shifter’s Sorrow: 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.

Strong transmutation; CL 15th; Craft Magical Arms and Armor, baleful polymorph; Price 12,780 gp; Cost 6,780 gp + 480 XP; Weight 10 lb.