Undead Sphere

The spell creates a sphere with a 20 foot radius. Creatures in that sphere have to make a dex save, a creature that fails the check suffers from 3d6 necrotic damage and 3d6 soul damage. After the damage is dealt, the sphere expands to the same amount of soul damage. Also the movementspeed lowers for 3d6 ms. In the next turn of the caster everybody who is in the sphere suffers from additional 3d6 necrotic damage.