Dreadthorn Shadowbind

You summon shadows to bind a target, restraining them with the power of darkness. Choose one creature within range that is large or smaller. The target must succeed on a Dexterity saving throw or be restrained by shadowy tendrils until the spell ends. While restrained in this way, the creature takes 3d6 necrotic damage at the start of each of its turns.

As an action, the restrained creature can make a Strength or Dexterity check (its choice) against your spell save DC. On a success, it frees itself from the shadowy tendrils and the spell ends.

While the creature is restrained, you can use an action on subsequent turns to tighten the tendrils, increasing the necrotic damage to 4d6 for that turn.