Restrained on a fail; 3d6 again each turn until it escapes.
Casting Time
Action
Range
90 feet
Duration
Concentration (up to 1 minute)
Components
V, S, M
a tentacle
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 that area into Difficult Terrain.
Each creature in that area makes a Strength saving throw. On a failed save, it takes 3d6Bludgeoning damage, and it has the Restrained condition until the spell ends. A creature also makes that save if it enters the area or ends it turn there. A creature makes that save only once per turn.
A Restrained creature can take an action to make a Strength (Athletics) check against your spell save DC, ending the condition on itself on a success.