Alyxian, Dirge of The Deep

Apotheonic Abjection. Upon reaching 1/2 health for the first time each day The Dirge of The Deep regains health equal to his maximum health and becomes Mythic. As long as he is Mythic opposing creatures who start their turn within 10ft of The Dirge of The Deep take 1d10 Cold Damage and must make a DC 17 Wisdom Save or be slowed until the end of their turn. While slowed this way a creature's speed is halved and it can take either an action or a bonus action on its turn, not both. Furthermore, any creature with more than one attack per action can instead make only one attack per action while slowed this way.

Divinely Blessed. Alyxian can’t be surprised and can’t be changed into another form against his will.

Legendary Resistance (3/Day). If Alyxian fails a saving throw, he can choose to succeed instead.

Multiattack. Alyxian makes two Grasping Hand attacks.

Grasping Hand. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 15 (3d6 + 5) force damage, and if the target is a Medium or smaller creature, it is grappled (escape DC 15). Alyxian has six hands, each of which can grapple one target.

Depths of Despair (Recharge 5–6). The Dirge of The Deep targets up to two creatures he can see within 120 feet of himself. Each target must make a DC 18 Wisdom saving throw, taking 14 (4d6) psychic damage and 14 (4d6) cold damage on a failed save, or half as much damage on a successful one.

The Dirge of The Deep 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. The Dirge of The Deep regains spent legendary actions at the start of his turn.

Attack. The Dirge of The Deep makes one Grasping Hand attack.

Aria of The Abyss (Costs 2 Actions). The Dirge begins a lamenting, wailing, song affecting all creatures in a 10-foot-radius sphere centered on a point The Dirge of The Deep can see within 60 feet of himself. A creature takes 18 (4d8) psychic damage when it enters that area for the first time on a turn or starts its turn there. The effect lasts until the end of The Dirge’s next turn, when the song fades.

The Dirge of The Deep Gains 2 mythic actions which can be spent on the options below after he becomes Mythic. The Dirge of The Deep becomes Mythic when it hits half health the first time. 

Attack. The Dirge of The Deep makes two Grasping Hand attacks.

Vortex of Retribution (Costs 2 Actions). The Dirge of The Deep summons one Watery Arm in each body of water that the Dirge does not currently occupy. Each Watery Arm moves on its own turn, has 35 Hp, a 15 AC, and makes two attacks on its turn +8 to hit, 2d6+8 Cold Damage on a hit.