Eldritch Cube A5E

A black, nonreflective, incorporeal 10-foot cube appears in an unoccupied space that you can see. Its space can be in midair if you so desire. When a creature starts its turn in the cube or enters the cube for the first time on its turn it must make an Intelligence saving throw, taking 5d6 psychic damage on a failed save, or half damage on a success.

As a bonus action, you can move the cube up to 10 feet in any direction to a space you can see. The cube cannot be made to pass through other creatures in this way.