Actions

Multiattack. The moon child uses its maddening presence and makes 5 attacks; 2 with its claws, 2 with its tentacles and 1 special attack. If a creature is hit by both claws attacks it takes an additional 13 2d12 slashing damage.   Claws. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 30 4d10+8 slashing + 11 2d10 force damage.   Tentacle. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 26 4d6+8 bludgeoning + 11 2d10 force damage.  

Special Attack

Rain of Blood (Recharge 5-6). The moon child conjures a rain of corrupted blood. Each creature within 40 feet of the moon child must make a DC 21 Constitution saving throw.
On a failed save a creature takes 31 9d6 necrotic damage and becomes afflicted by the corrupted blood for one minute.
On a successful save a creature takes half as much damage and is not afflicted.
As long as a creature is afflicted, it cannot regain hit points.
An afflicted creature repeats the saving throw at the end of its turn, ending the affliction on a successful save.
Creatures that are immune to being poisoned cannot be afflicted and any effect that heals the poisoned condition can also remove the affliction from a creature.   Lunar Gaze. The moon child releases a burst of pale, silvery light which diminishes every living creature of the moon child’s choice within 60 ft of it.
Each creature in the area must make a DC 20 Constitution saving throw.
On a fail, they're reduced to 1/10th of their current hit points.
This attack has no effect on constructs and undead. After using this attack the moon child can only take 1 legendary action until the beginning of its next turn.   Maddening Presence. Each creature of the moon child’s choice that is within 120 feet of the moon child and is aware of it must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute.
A creature repeats the saving throw at the end of each of its turns, ending the effect on itself on a success.
If a creature’s saving throw is successful or the effect ends for it, the creature is immune to the moon child's Maddening Presence for the next hour.

Legendary Actions

The moon child can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. The moon child regains spent legendary actions at the start of its turn.   Move. The moon child moves up to its speed without provoking opportunity attacks.
Tentacle. The moon child makes a tentacle attack.
Pounce (2 Actions). The moon child jumps up to 40 ft. and attacks with its claws against a target within its reach.
Blood Cloud (2 Actions). The moon child summons a cloud of blood at a point within 60 ft. of itself.

The cloud rains corrupted blood in a 40-foot high cylinder with a 10-foot-radius below it.

Each creature in that area must make a DC 21 Dexterity saving throw.

On a failed save a creature takes 13 (3d8) necrotic damage and unless the creature is immune to being poisoned it cannot regain hit points until the end of the moon child's next turn.

On a successful save a creature takes half as much damage and suffers no additional effects.