SRD:Psibane

Psibane: A psibane weapon is crafted to oppose psionic beings. When used against such creatures, its effective enhancement bonus is 2 higher than its actual enhancement bonus. It deals an extra 2d6 points of damage against psionic opponents. It bestows one negative level on any psionic creature attempting to wield it. This negative level remains as long as the weapon is in hand and disappears when the weapon is no longer wielded. This negative level never results in actual level loss, but it cannot be overcome in any way while the weapon is wielded. Psibane bows, crossbows, and slings bestow this ability upon their ammunition.

Strong clairsentience; ML 15th; Craft Psionic Arms and Armor, bend reality; Price +2 bonus.