Backbiter

Backbiter is an cursed spear +3 which can't be removed from the weapon slot without the Remove Curse spell and it inflicts 3 piercing to the wielder upon a successful hit. The weapon can inflict 1d6 +3 points of damage, has -3 THACO bonus and weighs 5 lbs. Despite the fact the statistics claim this weapon has speed factor of 6, it's actually 3 in the game files. This item appears in Baldur's Gate, Baldur's Gate: Enhanced Edition, Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition.

It's not known where this weapon can be gained in Baldur's Gate.

In Baldur's Gate II, this weapon can be found in the Underdark near the object that house the victims of the spell Imprisonment.

In-game description
"This cursed spear will appear as a magical spear, however when a combat situation arises, the wielder will attack an enemy and Backbiter will attack the wielder. For every attack made, Backbiter will attack the foe and also the wielder. This is a powerful spear, but one must ask if it is worth it in the end. The only way that Backbiter can be removed is by a remove curse spell."