Swarm Of Thralls

You summon a swarm of spectral thralls to harass your enemies. Choose a point within range; a 10-foot-radius sphere centered on that point becomes filled with thralls. Any creature that starts its turn in the area must make a Dexterity saving throw, taking 4d6 necrotic damage on a failed save, or half as much damage on a successful one. The area is also considered difficult terrain.