Random Magic Weapons (any level)

A bane weapon excels at attacking one type of creature. Against its designated foe, its effective enhancement bonus is +2 better than its normal enhancement bonus (so a +1 longsword is a +3 longsword against its foe). Further, it deals +2d6 points of bonus damage against the foe.
Aura: Moderate conjuration
Caster Level: 8th
Requirements: Craft Magic Arms and Armor, summon monster I
Price: +1 bonus
Source: Dungeon Master's Guide v.3.5