SRD:Unholy

Unholy: An unholy weapon is imbued with unholy power. This power makes the weapon evil-aligned and thus bypasses the corresponding damage reduction. It deals an extra 2d6 points of damage against all of good alignment. It bestows one negative level on any good creature attempting to wield it. The 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 (including restoration spells) while the weapon is wielded. Bows, crossbows, and slings so crafted bestow the unholy power upon their ammunition.

Moderate evocation [evil]; CL 7th; Craft Magical Arms and Armor, unholy blight, creator must be evil; Price +2 bonus.