Daelin's Gravity Well

A violet magic circle fill a 20-foot radius circle on the ground that you can see within range. For the duration, this circle 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 nad be restrained by the gravitational pull until the spell ends. A creature that starts its turn in the area and is already restrained by the increased gravity takes 3d6 bludgeoning damage.

A creature restrained by the gravitational pull can use its action to make a Strength or Dexterity check (its choice) agains your spell save DC. On a success, it fees itself.