The Court's Stampede

You open a space between this realm and the Umbral Court. This area is considered difficult terrain, and consists of a 20 foot sphere of murky violet-black darkness, interspersed with motes of starlight. Faint echoes of animal cries and a distant rumbling are audible within 30 feet of this sphere. When a creature enters the sphere, it takes 4d6 cold damage. If a creature starts its turn inside the sphere, it must make a dexterity saving throw, taking 4d6 force damage on a failed save, or half as much on a successful save.
A creature fully inside the sphere is considered blinded, and feels the rush of furred creatures in a stampede.