Cthulhu, the Ancient God of Death

Amphibious. Cthulhu can breathe air and water.

Legendary Resistance. (4/day) If Cthulhu fails a saving throw, he can choose to succeed instead.

Sense Spellcaster. Cthulhu senses spellcasters within 120 feet of it at will, as if it was blindsight. This trait otherwise works like the detect magic spell but isn't itself magical.

Godsight. Cthulhu can see anywhere into the Winds of Death God Plane at will.

God of Death's Last Wish. If Cthulhu hits zero hit points, he goes to phase two. (Mythic)

Insanity Invoking. Every round in combat with Cthulhu, all players and companions must succeed a (DC 15) intelligence saving throw. If they succeed, nothing happens. If they fail, they lose concentration on the current spell they are concentrating on.

The God Plane's Calling. If Cthulhu successfully banishes a player (Using banishment) that player goes to the God Plane for one round.

Immortal. Cthulhu does not age.

Phase Two's Size Increase. In phase two, he can use mythic actions, also he is increase to gargantuan size, and gains the [Ancient Draconic] move list. He cannot use the [Ancient Draconic] move list until phase two.

Immovable. Cthulhu cannot be moved against his will, and cannot have a condition that would set his movement to zero. (petrified, etc.)

Phase Two Wings. In phase two, Cthulhu's back rips open for a second, revealing wings. (Cthulhu can now fly 60ft.)

Destructive. Cthulhu does double damage to objects and structures.

Freedom of Movement. Cthulhu ignores difficult terrain, and magical spells can't reduce its speed or cause it to be restrained. It can spend 5 feet of movement to escape nonmagical restraints or being grappled.

The Pact. Cthulhu can offer one player immense power, usually to Cthulhu's gain, like if Cthulhu was dying. This player would receive the power, but usually at a cost, like shortened lifespan or deadly disease, that ultimately helps Cthulhu in the end.

Multiattack. Cthulhu makes six attacks of its choice, and one automatic [Tentacle] attack (If he spawned a Tentacle with a bonus action.) Cannot use [Ancient Draconic] move list until Phase Two.

Greatest of Swords Swing. Melee Weapon Attack: +7 to hit, reach 10ft., one target. Hit: 40 (8d8 + 8) slashing damage.

Reaping Claws. Melee Weapon Attack: +16 to hit, reach 5ft., one target. Hit: 18 (2d8 + 10) slashing damage.

Claw Pierce. Melee Weapon Attack: +12 to hit, reach 5ft., one target. Hit: 22 (4d10 + 2) piercing damage.

Miasmic Fog. Ranged Weapon Attack: +19 to hit, reach 5/15 ft. sphere radius, multiple targets. Hit: 9 (1d12 + 3) bludgeoning damage. If Miasmic Fog hits, target(s) take an additional 5 (2d8) necrotic damage.

RUNES OF THE GOD PLANE. Ranged Weapon Attack: +8 to hit, reach 5/30 ft., one target. Hit: 37 (3d20 + 7) force damage.

[Tentacle] Tentacle Slam. Melee Weapon Attack: +10 to hit, reach 5/30 ft., one target. Hit: 21 (3d12 + 3) bludgeoning damage.

[Tentacle] Tentacle Grab. Ranged Weapon Attack: +13 to hit, reach 5/30 ft., one target. Hit: 6 (1d8 + 2) bludgeoning damage. Target must succeed a DC 16 dexterity saving throw or be grappled.

[Tentacle] Tentacle Throw. If Cthulhu has any creature grappled, he can choose to throw them up to 60ft. away, every 10ft. the target takes additional 1d6 bludgeoning. (If they're thrown 60ft., they take 6d6 damage, if they were thrown 30ft., they take 3d6, etc.)

Necrotic Star Beam. Creates five beams in a pentagon pattern of green bright light for 5ft.  that start at Cthulhu and branch to 30ft. away. Once he casts this, it takes one round for it to take effect. After one round, if any players are in this beam, they take +20 to hit, reach 5/30 ft., multiple targets. Hit: 54 (8d12 + 6) Necrotic damage. Target must succeed a DC 13 Dexterity saving throw or be petrified until the end of their next turn.

Spellcasting. Cthulhu is an 20th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 22, +14 to hit with spell attacks). Cthulhu has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation, shocking grasp

1st level (4 slots): detect magic, identify, mage armor, magic missile, Comprehend Languages

2nd level (3 slots): detect thoughts, blindness/deafness

3rd level (3 slots): counterspell, fly, lightning bolt

4th level (3 slots): banishment, fire shield, arcane eye, locate creature, black tentacles

5th level (3 slots): cone of cold, scrying, wall of force, cloudkill, telekinesis

6th level (2 slots): mass suggestion, chain lightning

7th level (2 slots): teleport, delayed blast fireball, sequester

8th level (1 slot): mind blank, control weather, feeblemind

9th level (1 slot): power word kill, foresight

Spawn Tentacle. Cthulhu can use his bonus action to spawn a tentacle anywhere that is unoccupied space within 120ft. of Cthulhu. This tentacle makes one automatic [Tentacle] attack. (See actions for Tentacle Attacks). Each tentacle is an individual, and does not share the same stats as Cthulhu. Each tentacle has 16 in all stats, 35 HP, 15 AC, and move up to 20ft. each turn. When it moves, it is considered walking. A tentacle is not magically, and has no standard resistances, immunities, or vulnerabilities. Cthulhu can have a maximum of three alive tentacles at a time. If one dies, he can use another bonus action to replace it. Cthulhu starts battle with no alive tentacles.

Tentacle Trip. This bonus action cannot be used as the automatic [Tentacle] attack. Target must be 5/20ft. of the tentacle. This tentacle swipes at the creatures feet or support that is holding it up. This creature must succeed a DC 15 Dexterity saving throw or be knocked prone.

Sword Smash. If Cthulhu does a Greatest of Swords Swing attack, in the same turn, he can do Sword Smash. Target must within 5ft. of Cthulhu. +4 to hit target. If it hits, target takes 1d20+9 bludgeoning damage, and is stunned until its next turn. If creature is stunned, it automatically becomes un-stunned at the beginning of its turn, meaning it still gets to make its action and bonus action. {Basically disables their reaction, and does bonus damage to target.}

Piercing Screech. This move can only be used during Cthulhu's Phase Two. Cthulhu emits a piercing screech. All creatures within 20ft. of Cthulhu must make a DC 20 Wisdom saving throw or take 8d6 necrotic damage, and be deafened until the end of its next turn. If target succeeds, they take half damage. All targets within 120ft. {Excluding targets in 20ft.} must make a DC 15 Wisdom saving throw. If they fail, they take 4d6 necrotic damage. If they succeed, nothing happens.

Gateway to the God Plane. Cthulhu uses a forbidden rite of the Ancient Gods, and opens a gateway to the God Plane in an unoccupied space for three rounds. If a creature enters this portal, they are in the God Plane, but can leave, as the portal is open on both the Life Plane and God Plane. This portal is in the same spot every time, so if a creature is trapped within the God Plane and it's been three rounds, and they are trapped, if Cthulhu summons another portal, they can escape. While in the God Plane, Cthulhu can see them, just not hurt them unless he himself enters the portal. The portal takes up 5ft. of space, but any size creature can enter or exit if they touch the tile at any time.

Parry. Cthulhu can add 3 to his AC if hit with a melee attack, and he can see the target who hit him.

Wise Deflection. If Cthulhu needs to save against a spell targeting him only, if he saves this spell, the caster takes all damage that Cthulhu takes. Cthulhu still takes the damage.

Tentacle Shield. If Cthulhu must make a dexterity saving throw, he can use his reaction to move any tentacle within 10ft. of Cthulhu into the way. The tentacle automatically fails the dexterity saving throw and takes all the damage.

Cthulhu gets three legendary action points a turn. He charges 1d4 at the start of his turn. He cannot exceed three legendary action points, even if he rolls a four. He just recharges to three. All of his legendary actions are illusions, and true-sight (or other illusion/magic detecting items) can see through / know they are illusions.

[One Point] False / True Treasure. A chest spawns in the middle of the boss arena. Roll 1d2 (a coin), if heads, it is true treasure and contains one very rare. Once opened and loot collected, it disappears. If destroyed, the treasure fades to dust if it was true. If tails, it is false treasure, and if a player opens it, it deals 30 (5d12) slashing to them, then disappears. Cthulhu cannot use this again until the chest has been opened or destroyed.

[Two Points] Decoy Ring. Cthulhu creates up to four decoys of himself. These clones can mimic his move set, and do one attack on Cthulhu's turn. Each decoy has Cthulhu's stats, but only 10 HP. If two of four decoys are destroyed, the rest are destroyed as well. Cthulhu also swaps with one of these decoys when he deploys them (DM's choice of where). He can deploy them up to 60ft. away from his current position.

[Three Points] Yelp of Last Life. Cthulhu fakes his death, falling to the floor, and fading into golden dust (as all the other main bosses in WOD do.), and combat ends. He can move up to his movement speed and has the spell of greater invisibility cast on himself. He can then attack one player, his invisibility ending once he attacks. This invisibility cannot be seen unless an item / power specifically states it can see invisible creatures.

[Ancient Draconic] Fire. Cthulhu speaks the word "Fire" in Ancient Draconic, fire expels in a 60-foot cone. Each creature in that area must succeed on a DC 14 Dexterity saving throw. On a failed save, the target(s) take 10d10 fire damage. On a success, they take half damage.

[Ancient Draconic] Rise. Cthulhu speaks the word "Rise" in Ancient Draconic. All allied and non-hostile creatures in a 40ft. radius from Cthulhu raises from dead, or heal if they were already alive. They heal 4d8.

[Ancient Draconic] Death. Cthulhu speaks the word "Death" in Ancient Draconic. If the required target is within 60ft. of Cthulhu, they must make a (DC 15) wisdom saving throw, or do counter-ward (Ancient Draconic Word of Ward) as a reaction. If they fail the saving throw or don't do counter-ward, they take 10d20 necrotic damage. Cthulhu can only use this once a battle.