The Chains

The chains of Tharizdun lash out into the material plane. The caster chooses at 20ft square within range.

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 chains 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 chains can use its action to make a Strength or Dexterity check (it's choice) against your spell save DC. On a success, it frees itself.