Tentacles of the Deep

(2/long rest): When a creature within 5 feet of you hits you with a melee attack, you can use your reaction to conjure a watery tentacle that lashes out in retribution. The attacker must make a Dexterity saving throw, taking 2d6 bludgeoning damage on a failed save, or half as much on a success. On a failed save, their speed is also halved until the start of their next turn.