Backbiter (EFA - B)

Choose a melee weapon you can see within range. The next time that weapon is used to make an attack, it twists around so that the weapon strikes the wielder instead, with the attack roll applied against the attacker’s own AC. Once the weapon attacks its wielder, the spell ends, irrespective of whether or not the attack was successful. A sentient magic weapon can make a Wisdom saving throw to avoid the effect.