Umbra Regnum

Name	Umbra Regnum
Cooldown	at-will
Action	standard
Duration	concentration
Special	DC 23+
Power	umbra
Class	arcanist
Category	Control, Defense, Shaping

At-will, standard action, concentration, DC 23+; you overlay an area up to 300 feet in diameter with the essence of the Shadow Plane. The area becomes dim at best (bright light is reduced to dim; dim light becomes darkness). All shadows become deep and animate. The terrain warps subtly—colors desaturate, sounds become muffled, and the air chills.

Within the shadow realm:

You and creatures you designate gain advantage on Stealth checks, +2 AC, and resistance to necrotic damage.
Hostile creatures have disadvantage on Perception checks, and their speed is reduced by 10 feet.
Shadow creatures summoned within the area have double hit points.
Mundane light sources are suppressed entirely. Magical light is reduced by one step.
DC +4: the area increases to a 1-mile diameter.
DC +8: the overlay persists for 24 hours without concentration.
Powerful beings native to the Shadow Plane may take notice of this spell and investigate.