SRD

Black Tentacles

0-level (Cantrip) Conjuration

Squirming, ebony tentacles fill a 20-foot square on ground that you can see within range. For the Duration, these tentacles turn the ground in the area into difficult terrain.

When a creature enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or take 3d6 bludgeoning damage and be Restrained by the tentacles until the spell ends. A creature that starts its turn in the area and is already Restrained by the tentacles takes 3d6 bludgeoning damage.

A creature Restrained by the tentacles can use its action to make a Strength or Dexterity check (its choice) against your spell save DC. On a success, it frees itself.