Incorporeal Movement. The Hungering Shadows can move through other creatures and objects as if they where difficult terrain. It takes 5 (1d10) force damage if it ends it's turn inside and object

Affinity to the Dark. While obscured in shadow and darkness, the Gnawing Shadows can use the Hide action as a bonus action

Light Sensitivity. The Hungering Shadows has disadvantage on attack rolls, as well as Wisdom (Perception) checks that rely on sight while in bright light.

Shadow Summoner. As a bonus action on each turn the Hungering Shadows is able to, it summons a Shadow to drain it's victims before consuming their souls.

Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 11 (2d6 + 4) necrotic damage. If the Hungering Shadows had advantage on it's attack roll, add 7 (2d6) psychic damage 

Shadow Poison. Ranged Spell Attack: +7 to hit, range 30/120 ft., one target. Hit: 9 (4d4 + 4) poison damage. Each successful attack creates a stack of Shadow Poison on the target, at the beginning of the targets turn they must roll a DC 16 constitution saving through or take 3 (1d6) necrotic damage per stack.
A maximum of 5 stacks may applied to a single target

Demonic Revenge. The Hungering Shadows retaliates against the first successful attack against it each round. Lashing out with a Shadow Poison attack

The Hungering Shadows has a carefully conceived strategy for dealing with intruders into it's work, it will use one legendary action per round whenever it deems necessary.

Soul Catcher (1st Round Action). The Hungering Shadow activates 15-foot radius circle, centring on any point it can see within 120 feet, the ground glows with red demonic runes and any creature caught within must make a DC 14 Constitution saving through or have their maximum HP reduced by 25% for one minute. At the end of that time, they only regain half of the hit points they lost.

Disruption (2nd Round Action). The Hungering Shadow casts Banishment on one target with a DC 16, the target is sent temporarily to the Abyss, leaving behind a swirling pool of inky-red blackness in the air where they where banished. While banished the creature still is affected by Shadow Poison, if the creature dies while Disrupted it's soul is gifted directly to the Abyss

Demonic Purge (3rd Round Action). All creatures affected by the Shadow Poison are released in a wave of demonic energy. Instantly dealing another round of damage to all those creatures, they also have their movement halved for one round.
The Hungering Shadows is healed for half of the damage done by it's Shadow Poison burst