Rift to the Dreadscapes

As an action on your turn, you can choose a point within 5 feet of you to open the rift. Once opened, the rift stretches out from that point to a 20-foot-radius sphere. When a creature other than you enters the rift’s area for the first time on its turn, or starts its turn there, it must make a Constitution saving throw against your Transformation DC.

On a failed save, the creature suffers 10d10 necrotic damage, or half as much on a successful save. Undead creatures are immune to damage from this ability. The rift remains open for 1 minute, but closes if you become unconscious. Once you use this ability, you cannot use it again until you complete a long rest.