Tentacle Trap

Squirming, ebony tentacles surg out in search filling a 20-foot square on ground that you can see within range. For the duration, these tentacles wrap themselves tightly using their suction cups around a creature's legs.  

When a creature becomes affected for the first time on a turn, the creature must succeed on a Dexterity saving throw or take 3d6 skin ripping acidic 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 acidic 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.