Bramblewood's Twisting Thorns

Writhing, dark grey thorny vines fill a 20-foot square on ground that you can see within range. For the duration, these thorny vines 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 piercing damage and be restrained by the thorny vines until the spell ends. A creature that starts its turn in the area and is already restrained by the thorny vines takes 3d6 piercing damage.

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