Aspect of Kyuss

Initiative. This monster has an additional +13 bonus to its initiative rolls.

Legendary Resistance (5/Day). If the aspect fails a saving throw, she can choose to succeed instead.

Limited Magic Immunity. Unless he wishes to be affected, Kyuss is immune to spells of 4th level or lower. He has advantage on saving throws against all other spells and magical effects.

Multiple Reactions. Kyuss can take multiple reactions per turn, rather than only one per round. 

Regeneration. Kyuss regains 30 Hit Points at the start of his turn. 

Divine Aura. Any non-divine creature within 30' of Kyuss must make a DC25 CHA save or be stunned in awe of his divinity. A new save may be made at the end of the creatures turn. A creature that successfully saves is immune to Kyuss' Divine Aura for 24 hours.

Discorporation. If Kyuss is reduced to 0 hit points he falls into a pile of giant vermin (worms, maggots, etc.) that immediately attempt to escape by slithering through holes or burrowing into the earth and his equipment is banished to a demi plane only Kyuss can access.

Multiattack. Kyuss can use his Divine Aura and then make four Mace attacks.

Advanced Critical Strike  Critical Hit on Natural 18, 19 or 20; a critical strike deals x3 damage instead of x2 due to how heavy the ball is driving the axe or pick into a target. +19 

Executioner's Mace. Melee Weapon Attack: +19 to hit, reach 30 ft., one target. Hit: 23 (2d12 + 10) Bludgeoning/Piercing/Slashing damage plus (5d12+15) Necrotic or Psychic damage.

Godly Might. Once per turn, as a bonus action, Kyuss can dismiss 1 negative effect (magical, DoT, etc.) that is affecting him directly. 

Insightful Gaze. Once per round, whenever an attack that requires an attack roll targets Kyuss, he can gaze into the soul of the attacker, striking unease at their core and throwing them off balance. CHA save DC25 All subsequent attacks from that attacker are at disadvantage for the duration of the round on a failed Save, no effect if save successful.

Parry and riposte. You deflect your opponent's attack, then immediately make your own attack against which he is not at that precise instant defending. Parry: Kyuss chooses to Parry increasing his AC by +6. Riposte: He then makes an immediate melee attack after a successful Parry.

Absorb Elements. Kyuss can choose to absorb any Necromantic damage and turn it into negative healing energy.

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

Attack (1 action). Kyuss can make an attack with his mace instantly after an opponent's if the attacker is within range.

Worm Burst (2 actions). Kyuss selects a point he can see within 500 feet of him, conjuring necrotic worms. Each creature within a 20-foot radius of the point must make a DC 25 Dexterity saving throw, taking 55 (10d10)piercing damage plus 36 (8d8) necrotic damage and gaining a level of exhaustion on a failed save and half as much damage on a successful one.

Wave of Torment (3 actions). Kyuss slams his Mace into the ground, causing a devastating shockwave to travel in all directions. All creatures within 60 ft. must make a DC 25 STR saving throw and take 88 (16d10)   Force damage while also being knocked prone on a failed save, or half as much on a success.

Curse of Violence (3 actions). Upon dropping below half his maximum HP, Kyuss lets out an earsplitting screech of torment followed by an infernal curse. All opponents within 300 ft. that can hear this cry suffer 67 (15d8) psychic damage and must make DC 27 CHA saving throws. On a failure, the target is stunned by Kyuss for the next minute and can either use an action or bonus action, but not both on their subsequent turns for the duration. As slow spell. An affected creature may also make additional DC 20 CHA saving throws at the end of their turns to end the curse's effects. A remove curse spell may also end this effect for a target. 

Kyuss' Respite. Upon reaching 200 HP, Kyuss shrinks down to humanoid size and begins to levitate. He then splits off into 4 identical copies, each with an Executioner's Mace. This functions similarly to the Mirror Image spell except all four copies move independently of each other and can attack separately, they all retain Kyuss' initial initiative order. These are 4 independent creatures that all share Kyuss' essence and each one still gets 4 attacks. This is considered a bonus action.