You open a gateway to the Far Realm, a region infested with unspeakable horrors. A 20-foot-radius Sphere of Darkness appears, centered on a point with range and lasting for the duration. The Sphere is Difficult Terrain, and it is filled with strange whispers and slurping noises, which can be heard up to 30 feet away. No light, magical or otherwise, can illuminate the area, and creatures fully within it have the Blinded condition.
Any creature that starts its turn in the area takes 2d6Cold damage. Any creature that ends its turn there must succeed on a Dexterity saving throw or take 2d6Acid damage from otherworldly tentacles.
Using a Higher-Level Spell Slot
The Cold or Acid damage (your choice) increases by 1d6 for each spell slot level above 3.