Umbral Assault

You target a creature within range. The shadows of creatures within 5 feet of the target then turn against the first creature, attacking them from all sides. The target must make a Dexterity saving throw. The creature takes 3d6 necrotic damage for every creature within 5 feet of it of size Small or larger, up to a maximum of 24d6 on a failed save, or half damage on a successful one.