Source: Phandelver and Below - The Shattered Obelisk

Weapon (Greataxe), Rare (Requires Attunement)

Carvings of decapitated mind flayers adorn this greataxe’s metal blade. You gain a +1 bonus to attack and damage rolls made with this greataxe.

An Aberration hit with this greataxe takes an extra 1d12 slashing damage. If the Aberration is currently grappling a creature, the Aberration must succeed on a DC 15 Strength saving throw or release each creature it is grappling.