Ankarakan - The nightmare weaver

Legendary Resistance (5/Day). If they fail a saving throw, it can choose to succeed instead.

Threshold Damage: To be hurt by an attack, a threshold of 10% of the remaining health must be met/beaten. When below 5% of the monsters original health, only attacks per turn of damage equal or more to that amount can drop health to 0. 

Multiattack. The monster can use a web attack, followed by a bite and a stinger attack. 

Action Melee Attack. 

Bite. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 25 (3d10 + 8) piercing damage plus 14 (4d6) acid damage.

Stinger. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 21 (3d8 + 8) piercing damage. The creature must make a DC17 CON save. On a failure, the creature is paralyzed for 1 minute. The creature may repeat the saving throw at the end of their turns.

Action Ranged Attack. 

Web Strand. Ranged Weapon Attack: +13 to hit, reach 120 ft., one creature. Hit: The target is restrained (escape DC 18). The web strand can be attacked and destroyed (AC 12; 20 hit points; vulnerability to fire damage; immunity to bludgeoning, poison, and psychic damage)

The monster can take 1 legendary action per round and they must be at the end of another characters turn. 

Feed off the dark (Costs 1 Actions). As a legendary action, Ankarakan. if in dim or no light, can feed their HP for 2D20. 

Eye gaze (cost 1 action). As a legendary action, Ankarakan stares at their enemies within sight (up to 8). They must make a DC 18 CON save or 1 or the below random effects take place.

Roll a D12

1-3 - Fear takes over as you imagine thousands of spiders crawling over your body, devouring you. You are made prone and writhing in pain, scratching at your skin to free yourself. You take 4D6 slashing damage. You may attempt to pass the Save again at the start of your next turn, not losing your turn if you pass. 

4-7 - You gaze into the large eyes of wonder and are charmed for 3 turns. You are no longer hostile towards Ankarakan or it's followers. Roll another DC 18 CON save, if you fail, you feel hostile towards your companions and defend Ankarakan. You may attempt to pass the Save again at the start of your next turn, not losing your turn if you pass. 

8-10 - You feel webbing shroud your body encasing you in a cocoon. You become paralyzed for 3 turns. You may attempt to pass the Save again at the start of your next turn, not losing your turn if you pass

11-12 - Necrotic energy seeps into your mind, ripping your mind apart. You take 6D4 Necrotic damage.