Ungoliant Gloomweaver

Legendary Resistance (3/Day). If Ungoliant fails a saving throw, it can choose to succeed instead. If Ungoliant has no Legendary Resistances at the start of her turn, she gains one. 

Magic Resistance. Ungoliant has advantage on saving throws against spells and other magical effects from Clerics or other creatures with divine nature. 

Unlight. Ungoliant can surround herself  with darkness made by malice out of light. It has the power to pierce eyes, enter creature's heart and mind and strangle the very will (Read Lair Actions). No creature can see through this darknes unless iluminated by magical light of 9th level or higher. 

Multiattack. Ungoliant can make up to 3 attacks with her claws. Alternatively she can use her Bite or one of the abilities. 

Eldritch Claw. Melee Weapon Attack: +19 to hit, reach 20 ft., 1 target. Hit: 25 (3d8 + 10) slashing damage plus 16 (4d6) necrotic or acid damage.

Bite. Melee Weapon Attack: +19 to hit, reach 20 ft., 1 target. Hit: 25 (2d12 + 10) slashing damage plus 16 (30d4) piercing damage.

Devourer of Light. Ungoliant sends forward a wave of gloom, creating an area of darkness within 500 feet of her. This darkness supresses all spells and divine abilities. Ungoliant regains 30 hit points for each spell of 5th level or higher and 100 hit points for each spell of 6th level or higher. 

Web of Eternal Hunger. Ungoliant covers a 120-foot cube with her webs, which are made of pure darkness and shadow. Creatures cought in these webs must make a DC 25 Strenght or Dexterity saving throw. On a failure creatures become restrained and take 8d10 necrotic damage at the start of each of their turns and their maximum hp is reduced by the same amount if they fail DC 23 Constitution save. Ungoliant regains hit points equal to twice the amount of damage dealt. 

Insatiable Void (1/day). Once per day, Ungoliant can summon the Insatiable Void within her, revealing her true nature. All creatures within 300 feet must make a DC 25 Strenght saving throw or be pulled 60 feet closer to her and take 12d10 force damage. Creatures and objects that end their turn within 30 feet of her are pulled into a demiplane of complete darkness. Within this demiplane, creatures experience eternal hunger, loosing all hit point recovery and taking 10d10 psychic damage per round. Escaping the damiplane requires a successful DC 20 Charisma saving throw made at the end of each turn. 

Abyssal Venom. Ungoliant can use a venomous bite attack as an action, dealing 5d12 piercing damage. In addition, the venom spreads into the targes bloodstream, inflicting additional 10d12 necrotic damage at the start of each of the creature's turns and looses 10 feet of movement each time. The creature is unable to maintain or cast spells that require concentration. The venom effect can only be removed by a Wish spell or similar Divine Intervention. 

Devour. When a creature drops below 50% hit points Ungoliant can move to half of her speed and make one bite attack against that creature.

Ungoliant can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Ungoliant regains spent legendary actions at the start of her turn.

Change Form (Costs 2 Actions). Ungoliant can change her form at will. In battle, she choses one phisical damage type and gains immunity to it untill the start of her next turn. It can't choose the same damage type each turn. 

Satiate Hunger (Costs 2 Actions). Ungoliant can make one Bite attack. If the target creature has half of it's hit points or less Ungoliant has advantage on the attack. 

Shadow Crawl (Cost 1 Action). Ungoliant covers herself in Unlight, she can teleport to any place in range of 60 feet. After this, she appears from the Unlight and all creatures must make DC 24 Strenght saving throw or be pushed away 5 feet for every 1 point of failed check. 

Extinguish Life (World Eclipse only). Ungoliant concentrates eclipse power in 10 feet radius within a point. All creatures within radius must succeed on DC 30 Constitution saving throw or take 18d8 necrotic damage that ignores resistances or immunities. Ungoliant restores hit points equal to damage dealt.

World Eclipse. When Ungoliant is reduced to half of her hit points, she activates her mythic ability, gaining access to new legendary actions. Ungoliant creatres a total eclipse over the material world for 10 minutes or until she dies. All magical and natural light ceases to exist. All radiance spells of 8th level or lower are extinguished and can't be cast while the eclipse exists.