You create a dark orb in a point of space that you can see within range. It is Large size, with a diameter of ten feet. When you cast this spell, all creatures whose space is occupied by the dark orb must make a Constitution saving throw, taking 2d8 necrotic damage on a failed save, or half as much on a successful save. As an action on your following turns until this spell ends, you can move the dark orb up to 30 ft, but no more than 120 feet away from you.