A spite weapon is, much like a bane weapon, designed to fight a specific creature type. When used to attack a creature of that type, a spite weapon automatically overcomes its damage reduction (even if the damage reduction cannot normally be overcome.)
Moderate conjuration; CL 8th; Craft Magic Arms and Armor, summon monster IX; Price +5 bonus.

As a DM, you may not want to allow PCs to use this item as it will make a lot of monsters easier to defeat. It might be useful as a one time thing, something that can help the PCs overcome a single powerful creature with massive damage reduction.

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