Mordenkainen's Lost Notebook

Blacksphere

4-level Evocation

A burst of force erupts in a 10-foot radius sphere centered at a point you can see within range. Creatures caught within the area must make a Dexterity saving throw or take 4d6 force damage on a failed save, or half as much on a success In addition, the sphere’s area is heavily obscured by dark mists and remains in place around creatures caught within while you maintain concentration. A creature caught within the sphere can try to force its way through the barrier by using its action to make a Strength check against your spell save DC. On a success, the creature can move through the barrier but loses half its movement. On a failed Strength check, the creature takes 1d6 force damage and remains caught within the sphere.   The sphere blocks line of effect from one side to the other and blocks all ranged attacks from crossing the barrier
At higher levels: When you cast this spell using a spell slot of 5th level or higher, the force damage from the initial burst increases by 1d6 for every slot level above 4th.