Alcatraz

Skill Proficiencies: Cthulhu is proficient in Intimidation and Persuasion checks.

Elemental Demise: Should Cthulhu perish, its body will disintegrate into a warm breeze with scatters of dust, leaving a form of it's equipped items behind.

Amphibious: Cthulhu can breathe air and water.

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

Siege Monster: Cthulhu deals double damage to objects and structures.

Special Equipment: Cthulhu carries a Staff of the Forgotten One and wears a Talisman of the Sphere, as well as carries a Sphere of Annihilation. In its offhand, it carries a scimitar.

Rejuvenation: Cthulhu's' body turns to dust, should it die. after 1d10 days, a new body will be composed with all hit points and abilities/gear.

Turn Resistance: Cthulhu has advantage on saving throws against any effect to turn undead.

Spellcasting: Cthulhu is a 20th level spellcaster who uses Intelligence for most of its spells(spell save DC 23, +15 to hit), and also uses Charisma(spell save DC 20, +12 to hit) for select spells. The following list is prepared, and uses Intelligence:

Cantrips(at will): mage hand, ray of frost, shocking grasp

1st level(at will): ray of sickness, shield

2nd level(at will): arcane lock, knock

3rd level(at will): animate dead, counterspell

4th level(3 slots): blight, ice storm, phantasmal killer

5th level(3 slots): cloudkill, hold monster, wall of force

6th level(3 slots): chain lightning, circle of death, disintegrate

7th level(3 slots): finger of death, plane shift, teleport

8th level(2 slots): maze, mind blank

9th level(2 slots): power word kill, time stop

These spells are prepared, and can be switched out with any spell in the wizard's spell table:

at will:

- detect evil and good

- detect magic

- thunderwave

3 per day:

- create food and water

- tongues

- wind walk

1 per day:

- conjure elemental(must be an air elemental)

- creation

- gaseous form

- invisibility

- major image

- plane shift

Ice Walk: Cthulhu can move across and climb icy surface without needing to make an ability check. Additionally, difficult terrain composed of ice snow doesn't cost it extra movement.

Magic resistance: Cthulhu has advantage on saving throws against spells and other magical effects.

Spell Immunity: Cthulhu is immune to three spells chosen by its master: Power Word Kill, Time Stop, and Dominate

(These links come from the D&DBeyond website, the Monster's Manual, as well as the roll20 and ******* websites)

Multiattack(scimitar): Cthulhu  strikes three times with its scimitar.

Scimitar: +17 to hit, reach 30 ft., 2d6 + 5 slashing + 1d6 lightning damage

Create Whirlwind: Cthulhu creates a 10 ft. wide 30 ft. cylinder of swirling magical air within 120 ft. of sight. Lasts until concentration breaks, any other creature entering makes a DC 18 Strength check or be restrained. It can be moved up to 60 ft. as an action, and trapped creatures follow. Creatures can become free by succeeding the check and taking the nearest empty space.

Bite: +17 to hit, 5 ft. reach, one target. 3d8+10 piercing damage. If the target is Large or smaller, and grappled by Cthulhu, then it is swallowed, ending the grapple. It becomes blinded and restrained, has complete cover from outside attacks, and takes 12d6 acid damage at the start of Cthulhu's turn. If Cthulhu take 50+ damage on a single turn from a captive, Cthulhu makes a DC25 Constitution saving throw at the end of the turn or regurgitate all creatures, who fall prone within 10 ft. of it. Should Cthulhu die, they are no longer restrained and can escape using 15 ft. of movement, exiting prone.

Multiattack(tentacle): Cthulhu makes three tentacle attacks. 

Tentacle: +17 to hit, 30 ft. reach, one target. 3d6+10 bludgeoning damage and target is grappled(escape DC of 18). Target is also restrained, and up to 10 targets can be this way at once(one per tentacle).

Fling: Cthulhu yeets a Large or smaller grappled creature up to 60 ft. in a random direction, and knocked prone. If thrown against a surface, they take 1d6 bludgeoning damage for every 10 ft. of distance. If another creature was hit, they must make a DC 18 Strength saving throw or fall under the same effects.

Lightning Storm: Cthulhu creates three bolts of lightning, each of which can strike a separate target within 120 ft. Target(s) must make a DC 23 Dexterity saving throw or receive 4d10 lightning damage on a fail. On a success, damage is halved.

Paralyzing Touch: +17 to hit, 30 ft. reach, one target. 3d6 cold damage, targets must make a DC 23 Constitution saving throw or be paralyzed for 1 minute. They can repeat the throw at the end of its turns to reverse the effect.

Staff(+3 Quarterstaff): +20 to hit, 30 ft. reach, one target. 1d6+4 bludgeoning + 3d6 necrotic damage

Invoke Curse: Cthulhu expends a charge from the Staff of the Forgotten One to target a creature within 60 ft. The target must succeed a DC 23 Constitution saving throw or be cursed, denying healing and applying vulnerability to necrotic damage until cleansed via greater restoration, remove curse, etc.

Frightful Presence: Each creature or Cthulhu's choice that is within 120 feet of it and aware of it must succeed on a DC 16 saving throw or become frightened for 1 minute a creature can repeat the saving throw at t he end of the creature's 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 Cthulhu's Frightful Presence for the next 24 hours.

Cold Breath(recharge 5-6): Cthulhu exhales an icy blast in a 90-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 16d8 cold damage on a failed save or half as much damage on a successful one.

Breath Weapons(recharge 5-6): Cthulhu uses one of the following breath weapons:

--Fire Breath: Cthulhu exhales fire in a 90-foot cone. Each creature in that area must make a DC 24 Dexterity saving throw, taking 13d10 fire damage on a fail, or half on a success.

--Weakening Breath: Cthulhu exhales gas in a 90-foot cone. Each creature in that area must succeed on a DC 24 Strength saving throw or have disadvantage on Strength-based attack rolls,  Strength checks, and Strength saving throws for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Change Shape: Cthulhu magically polymorphs into a humanoid or beast that has a challenge rating no higher than its own, or back into its true form. It reverts to its true form if it dies. And equipment it is wearing or carrying is absorbed or borne by the new form(Cthulhu's choice). In a new form, Cthulhu retains its alignment, hit points, Hit Dice, ability to speak, proficiencies, Legendary Resistance, lair actions, and Intelligence, Wisdom, and Charisma scores, as well as this action. Its statistics and capabilities are otherwise replaced by those of the new form, except any class features or legendary actions of the form.

PC Capability: Cthulhu is capable of emulating any bonus action that an adventurer could make, if only to display the futility of their efforts.

Counterspell: cast the Counterspell spell.

Legendary Tokens: Cthulhu can use 3 Legendary Tokens per round, each action separated by at least one turn. It can make one Legendary Action at the end of any creature's turn, besides themselves. All 3 tokens recharge at the beginning of Cthulhu's turn.

Tentacle Attack or Fling(1 token): Cthulhu makes a Tentacle Attack or Fling.

Lightning Storm(2 tokens): Cthulhu uses Lightning Storm.

Ink Cloud(3 tokens): While underwater, a 60 ft. radius ink cloud appears. It spreads around corners, and the area is heavily obscured to everyone besides a kraken or Cthulhu. Any creature ending their turn inside(besides Cthulhu) must make a DC 23 Constitution saving throw or take 3d10 poison damage(half as much on success). Strong currents disperse the cloud, or it disappears at the end of Cthulhu's next turn.

At-Will Spell(1 token): Cthulhu casts one at-will spell.

Melee Attack(1 token): Cthulhu uses Paralyzing Touch or one swing with a weapon.

Frightening Gaze(2 tokens): Cthulhu stares into a target within 10 ft. visibility. They must succeed a DC 20 Wisdom saving throw or become frightened for 1 minute.

Talisman of the Sphere(2 tokens): Cthulhu uses the Talisman of the Sphere to move its Sphere of Annihilation up to 90 ft.

Disrupt Life(3 tokens): Every creature within 20 ft. of Cthulhu must make a DC 20 Constitution saving throw or take 12d6 necrotic damage on a fail(half as much on a success).

Detect: Cthulhu makes a Perception check.

Wing Attack(2 tokens): Cthulhu beats its wings. Each creature within 15 feet off it must succeed on a DC 25 Dexterity saving throw or take 2d6+10 bludgeoning damage and be knocked prone. Cthulhu can then fly up to half its flying speed.

There are no mythic actions available for Cthulhu as of this moment.