Avatar of Darkness

Darkness Incarnate. Any magical light that is produced by anything lesser than a 9th-level spell is dispelled when it touches the Avatar of Darkness. It can also see through magical darkness up to a distance of 300 feet.

Part of the Great Dark. When the Avatar of Darkness is in dim light at start of its turn it regains 10 hit points. If it is in darkness at the start of its turn it regains 30 hit points. 

Magical Resistance. The Avatar of Darkness has advantage on saving throws made against spells and magical effects.

Spellcasting. The Avatar of Darkness can cast the following spells at will (spell save DC 20, +12 to hit with spell attacks): Darkness, Mage Hand (invisible, at 120 ft. range)

It can also cast the following spells a certain number of times each day (spell save DC 20, +12 to hit with spell attacks): 
2/day each: Greater invisibility (self only), Far Step
1/day: Maddening Darkness

Multiattack. The Avatar of Darkness makes two Slam attacks.

Slam. Melee Weapon Attack: +13 to hit, reach 20 ft., 1 target. Hit: 33 (4d12 + 7) force damage. Any creature within 10 feet of the target (including the target) must make a Dexterity Saving Throw (DC 21) or take 14 (4d6) bludgeoning damage.

Shroud. The Avatar of Darkness draws in the shadows surrounding it and creates a protective barrier around itself. For the next minute it loses its vulnerability to radiant damage and regains 26 (4d12) temporary hit points at the end of each of its turns. While this ability is active, the Avatar of Darkness isconsidered to be in darkness, can not move or take any actions other than the dodge action and automatically fails Dexterity Saving Throws. The Avatar of Darkness can end this ability early at the start of its turn as a free action.