Higher CR: This creature has a CR of 55, not 30, and upon defeat this will reward 1,620,000 xp.

Awakening (Recharges after a short or long rest). If Zynthedenth were to be reduced to 0 hit points, its current hit point total instead resets to 50,000 hit points, it recharges all abilities, and it regains any expended uses of its legendary resistance. Additionally, Zynthedenth can now use the options in the "Mythic Actions" section for 1 hour. Award a party an additional 1,620,000 XP (3,240,000 XP total) for defeating Zynthedenth after his Awakening activates. 

Life Steal. Zynthedenth gains 1 Max Health for every 100,000,000 creatures that have ever died. When Zynthedenth directly kills a creature, he gains 1d4 max health, and if that creature is a humanoid, they are reanimated as a skeleton or zombie under Zynthedenth's control, as though through the create undead spell. Zynthedenth can choose to forgo the hit point maximum increase and instead transform them into a shadow, ghast, or ghoul.

Regeneration. At the start of Zynthedenth's turn, If he has not taken radiant damage since the end of his last turn, he heals for 8d10 health.

Light Sensitivity. While in direct sunlight, Zynthedenth takes triple damage and has disadvantage on attack rolls, saving throws, and ability checks.

Turn Undead Immunity. Zynthedenth is immune to all effects that turn undead.

Storm of Darkness. Zynthedenth can use a bonus action to create or dispel a 1000 ft. storm around him that obscures the sun in a way that acts as though it were total darkness during the day, and complete darkness at night. Creatures with darkvision cannot see in the complete darkness at night. All non undead creatures within the storm take 2d12 necrotic damage at the start of every one of their turns.

Deadly Aura. All creatures within 5 ft. of Zynthedenth take 8d12 necrotic damage at the start of their turns or when Zynthedenth is hit with a melee attack.

Flaming Trail. When Zynthedenth moves, he leaves behind  a trail of green flames. Any creature who ends their turn in the fire or moves into it must make a DC 22 Dex saving throw, taking 4d12 fire plus 3d12 necrotic damage on a failed save, or half as much on a success. The fire lasts for 1 minute, or until otherwise removed.

Soul Rend. When Zynthedenth hits a creature with an attack, roll a d4. On an even number, the target must succeed on a DC 29 Wis saving throw, or be afflicted with soul rend. A creature can repeat the save at the start of each of their turns, ending the effect on a success.

Incorporeality. At will and while this creature has not taken damage within the last 1 minute, Zynthedenth can become incorporeal, which causes him to be unable to be targeted by effects, and capable of passing through solid matter. This creature becomes corporeal again after a week in this state or at will. After a week of incorporeality, Zynthedenth must wait one day to become incorporeal again. If Zynthedenth takes an action that deals damage to a target while incorporeal, he becomes corporeal.

Unsurprising. This creature cannot be suprised and always goes first in initiative.

Omniscient. While concentrating and out of combat, Zynthedenth can see everywhere, as though with normal vision. If a creature is being watched in this manner, they feel a sense of something looking at them.

Omniminded. Zynthedenth can concentrate on up to six spells or other effects at once. He also has advantage on saving throws to keep concentration. If he were to break concentration, only one thing he is concentrating on would end, and the others would have to be broken separately.

Antiatunement. When Zynthedenth hits a creature , they become unattuned to one of their magic items.

True Strike Aura. All creatures within 100ft. have disadvantage on attack rolls made against this creature. This creature has advantage on attack rolls against creatures within 100ft. of him.

Soul Draining. When a creature is damaged by one of Zynthedenth’s attacks, their Max Health is permanently reduced by 1d6.

Dark Lord. Any creature within 200ft. that has an evil or unaligned alignment that is not a player character must make a DC 22 Wis saving throw at the start of every one of their turns or become permanently under this creature’s control. 

Denial, Anger, Bargaining, Depression, Acceptance. If a creature within 200 ft. Is experiencing grief, they must roll a DC 22 Wis saving throw at the start of every one of their turns or become permanently under this creature’s control.

Limited Magic Immunity. Zynthedenth is immune to the effects of spells of 6th level or lower unless he chooses to be. He also has advantage on saving throws against spells and other magical effects.

Legendary Resistance. (5/day): If Zynthedenth fails a saving throw, he can choose to succeed instead..

Alter The Odds (1/day). When a creature rolls for damage, Zynthedenth can choose to change the rolls of all dice to whatever numbers he chooses. For example, if a creature casts fireball at third level, Zynthedenth can change the damage so that it deals between 8 and 48 damage.

Divination (3/day). When a creature makes an attack roll, ability check, or saving throw, Zynthedenth can choose whether it succeeds or fails. This ability can be used before or after the dice is rolled.

Absorbant Barrier. When a creature makes a ranged magic attack against this creature, he heals instead of taking damage, and is immune to any other effects the spell may have unless he chooses to be.

Antimagic Cone. Zynthedenth can use a free action to enable or disable an antimagic cone that extends in a 60ft. cone from Zynthedenth's gemstone eye. This creature and any magical effects created by this creature are unaffected by this cone.

Antiantimagic. Zynthedenth is immune to all anti magic effects.

Minmax Obliterator. This creature deals triple damage to players that are ruining the fun of the rest of the party.

Magic Weapons. Zynthedenth’s weapon attacks are magical.

Omniproficiency. Zynthedenth is proficient in all skills.

Eldritch Invocations. Zynthedenth has all Warlock pact abilities. From the pact of the chain he has a familiar imp, he uses Zynthedenth’s Soulblade as his pact of the blade weapon, and has the book of shadows and talisman. Zynthedenth can grant himself 10 eldritch invocations from the Warlock eldritch invocation list, and can change which ones he uses after a long rest. He is considered a level 30 warlock for the purposes of eldritch invocation restrictions.

Metamagic. Zynthedenth has 30 sorcery points, and can spend them on any of the options on the Sorcerer metamagic options when he casts a spell.

Create Magic Item. Zynthedenth can create magic items, requiring a lower amount of time and gp to make them.

• Common: 1 action, 5gp
• Uncommon: 1 minute, 20gp
• Rare: 1 hour, 50gp
• Very Rare: 1 day, 100gp
• Legendary: 3 days, 250gp

Aspect of Zynthedenth. Zynthedenth can create an aspect of him, which s controlled directly by him and can perform tasks that Zynthedenth doesn’t want to do himself, be they too mundane or dangerous. He can create up to one aspect per week, or once per day when Zynthedenth is in The Realm of Death.

Unholy Spellcasting. When Zynthedenth casts a spell that deals radiant damage, it instead deals necrotic damage.

Innate Spellcasting. Zynthedenth is a 30th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 38, +29 to hit with spell attacks). Zynthedenth has following spells prepared:
(At will): All cantrips-8th level spells except simulacrum and clone

(5/day): Every ninth level spell except wish.

(3/day): Spells upcasted up to 15th level.

Action Surge (3 times per short or long rest). Zynthedenth takes three actions, of which none of them can be multiattack.

Multiattack. Zynthedenth makes two deathly tendril or ethereal grab attacks and a soul orb attack,

Deathly Tendrils. Melee Weapon Attack: +29 to hit, reach 30 ft., 1 target. Hit: 30d20 necrotic damage.

Soul Orb. Ranged Weapon Attack: +29 to hit, range 30/500 ft., 10ft sphere. Hit: 40d20 psychic damage + 5d12 necrotic damage. On a hit, the creature becomes cursed. The curse disrupts their thoughts with horrible nightmares. While cursed, the ceatue gains no benifits from short or long rests. If a short or long rest is attempted, the creature must succeed on a DC 30 Wis saving throw or take 12d12 physic damage. After three failures, the creature becomes under the permanent control of Zynthedenth. The curse lasts for 2d12 + 5 days or until otherwise removed.

Etheareal Grab. Melee Weapon Attack: +29 to hit, range 10ft., 1 target. Hit: 30d20 piercing + 15d20 necrotic damage. The target is now grappled (Escape DC 28).

Soulsteel Stab. Melee Weapon Attack: +28 to hit, range 20ft., 1 target. Hit: 30d20 piercing damage. Creates a soulsteel sword and flings it at the target. On a hit, the impaled target takes 2d20 necrotic damage at the start of every one of their turns until the sword is removed. To remove the sword the creature must succeed on a DC 22 Con saving throw.

Death Laser. Ranged Magic Attack: +32 to hit, range 1000 ft., 5ft. line. Hit: 50d20 necrotic damage. If a creature dies from this attack, Zynthedenth heals for 50d20 health. The air disrupted by this attack lingers with its effects for one minute. If a creature enters the area during that duration or ends their turn there, they take 8d12 necrotic damage.

Flame Eruption. Zynthedenth erupts into a column of flames. All creatures within 10 ft. must make a DC 28 Dex saving throw or take 12d8 fire plus 5d8 necrotic damage. Zynthedenth then appears in an unoccupied location within 5 miles, and can take another action.

Ultra Soul Blast. Magic Attack: (3/day):  Every time Zynthedenth deals 100 damage, he gains a charge point. He must have at least one charge point to use this ability, and using it expends all charges. Zynthedenth releases a blast of charged up necrotic energy, annihilating anything in sight. All creatures not friendly to Zynthedenth within charge * 10 ft. must succeed on a DC 20 + charges Wis saving throw or take charge * 2d20 necrotic + charge * 1d20 force damage. If a target fails the saving throw by 5 or more, they are blasted 1d6 * 5ft away and knocked prone.

Ritual Dagger. Zynthedenth creates a short dagger inscribed with an emerald on its hilt, with a short curved blade. The blade is stabbed into the heart of a creature within 20 ft., and the creature takes 1d4 true damage. If a creature is reduced to 0 hit points by this attack, they die and their soul is stored in the emerald in the dagger. Zynthedenth cannot dispel a dagger that contains a soul, and can have a maximum of 12 creatures stored in daggers at once. 
A soul stored within a dagger retains the stats it had in its previous life, but loses all equipment. Zynthedenth can use an action to summon the creature as a ghostly green apparition of its previous self. This creature is under Zynthedenth’s control and can be directed to take actions by him without using an action. When the creature is reduced to 0 hit points, their soul is returned to the dagger. If the gemstone in the dagger’s hilt is destroyed, the dagger crumbles to dust and the creature’s soul is released and returns to its body if that is still possible. Zynthedenth can dispel a dagger without a soul in it at will.

Ultra Word Kill. (Three times per short rest) Kills a creature with 300 health or less.

Release Death. All bones or corpses of creatures within 100 ft. become animated undead and under this creature’s control.

Undead Army. (1/day): Summons 1d100 + 20 skeletons, 1d100 Shadows, 5d20 Zombies, 2d20 + 10 Warhorse skeletons, 1d12 + 8 Minotaur Skeletons, and 1d4 Ancient Black Shadow Dragons.

Summon Lichs. (1/day): Summons 1d6 - 1 (min 1) lichs in a 60ft. area around Zynthedenth. The phylacteries of the lichs are stored in objects of this creature’s choice, and are permanently under his control.

Summon Minion (Recharge 4-6). Summons an undead or fiend with a challenge rating of 30 or less. The creature manifests in an open space within 120 ft. The creature has its own initiative, but takes orders from Zynthedenth (no action required by him). 

Corrupting Whisper. Zynthedenth telepathicly whispers quietly into the ear of its target, speaking about their deepest desires and persuading them to join him. They must succeed on a DC 25 Wis saving throw or be under Zynthednth’s control for 1 day. If the controlled creature is forced to attack something they think friendly, they are able to reroll the saving throw. The spell ends on a success.

Undead Curse. Zynthedenth touches a creature, and they become cursed. The creature begins to wither away, their flesh rotting and falling off. Every day the creature’s hit point maximum is reduced by 1d10. If the creature’s maximum hit points reaches 0 in this manner, they die and are reanimated as an undead version of them, usually skeletal. For example, most humanoids would be reanimated as a skeleton or lich, and a dragon would become a dracolich.

Necrotic Charge (Recharge 5-6). When Zynthedenth next makes a melee attack, it deals an extra 24d6 necrotic damage.

Soul Powered Shield. Zynthedenth's AC increases by 1 and he gets a +1 to all saving throws for each creature he has killed within the last 24 hours. This effect lasts for 1 minute. When Zynthedenth uses this ability, the counter resets.

Spell. Zynthedenth casts a spell if 5th level or lower.

Reaction Attack. When a creature makes a melee attack against Zynthedenth while they have disadvantage, Zynthedenth can use his reaction to make a melee attack against the creature.

Shield. When Zynthedenth is attacked, he can use his reaction to increase his AC by 4 and grant himself a +4 to all saving throws for the duration of the attack. If a creature deals damage to Zynthedenth while the shield is active, the creature takes damage equal to one fourth of the total damage of the attack (rounded down).

Zynthedenth 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. This creature regains spent legendary actions at the start of its turn.

Deathly Tendrils. Zynthedenth uses his Deathly Tendrils attack.

Spell. Zynthedenth casts a spell of 6th level or lower that has a casting time of 1 action or bonus action.

Withering Cone (Costs 2 actions). Zynthedenth blasts out a 80 ft. cone of mist infused with necrotic energy. Each creature within range of the mist that is not undead must succeed on a DC 26 Con saving throw or become withered until the start of Zynthedenth's next turn. A withered creature deals half as much damage on all of their attacks, and takes an additional 2d12 necrotic damage when they are hit by an attack.

If Zynthedenth has activated its awakening trait within the last hour, it can use the options below as legendary actions.

Necrotic Blade. Summons a soulsteel sword and slashes it through the air. All creatures within 10 ft. must make a DC 25 Dex saving throw. On a failure the creature takes 5d12 necrotic plus 5d12 slashing damage. A creature hit by this attack has their soul ripped apart. They must succeed on a DC 14 Wis saving throw or be reduced to 0 hit points, and automatically fail their first saving throw.

Necrotic Spears (Costs 2 actions). Zynthedenth creates six spears of necrotic energy, and launches them at up to six targets, or can have multiple spears hit a single target. For each spear flung at a target, it must succeed on a DC 22 Dex saving throw or take 12d12 force plus 8d12 necrotic damage, and have their movement speed reduced by 5ft. (min 0ft.) until the end of their next turn.

Summon Dracolichs (Costs 3 Actions). Summons 1d4 Ancient Dracolichs within 60ft. of Zynthedenth. The dracolichs are permanently under this creature’s control