Source: Princes of the Apocalypse

Weapon, uncommon

This boomerang is a ranged weapon carved from griffon bone and etched with the symbol of elemental air. When thrown, it has a range of 60/120 feet, and any creature that is proficient with the javelin is also proficient with this weapon. On a hit, the boomerang deals 1d4 bludgeoning damage and 3d4 thunder damage, and the target must succeed on a DC 10 Constitution saving throw or be stunned until the end of its next turn. On a miss, the boomerang returns to the thrower’s hand.

Once the boomerang deals thunder damage to a target, the weapon loses its ability to deal thunder damage and its ability to stun a target. These properties return after the boomerang spends at least 1 hour inside an elemental air node.