Source: Tales from the Yawning Portal

Weapon (spear or javelin), very rare (requires attunement)

You gain a +2 bonus to attack and damage rolls made with this magic weapon. When you throw it, its normal and long ranges both increase by 30 feet. and it deals one extra die of damage on a hit. After you throw it and it hits or misses, it flies back to your hand immediately.

Curse. This weapon is cursed, and becoming attuned to it extends the curse to you. Until the curse is broken with Remove Curse or similar magic, you are unwilling to part with the weapon, keeping it within reach at all times. In addition, you have disadvantage on attack rolls made with weapons other than this one.

Whenever you roll a 1 on an attack roll using this weapon, the weapon bends or flies to hit you in the back. Make a new attack roll with advantage against your own AC. If the result is a hit, you take damage as if you had attacked yourself with the spear.