C'thulhu

Eldritch Resistance (5/Day). If Cthulhu fails a saving throw, he can choose to succeed instead.

Innate Spellcasting. Cthulhu's innate spellcasting ability is Charisma (spell save DC 22). It can cast the following spells, requiring no material components:

At will: dream, plane shift, teleport

Non-Euclidean Madness. A creature that starts its turn within 240 feet of Cthulhu must succeed on a DC 25 Wisdom saving throw or become frightened 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. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to this ability for the next 24 hours.

Palingenesis. When Cthulhu is reduced to 0 hit points or killed, only his physical shell is destroyed. It will reform at a later point.

Regeneration. Cthulhu regains 15 hit points at the start of his turn.

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

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

Magic Weapons. Cthulhu's weapon attacks are magical.

Multiattack. Cthulhu uses its Otherworldly Gaze. He then makes four attacks: two with his wings and two with his claw, or two with his tentacles and two with his claw.

Action Melee Attack. Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 37 (5d10 + 10) slashing damage.

Tentacles. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 26 (3d10 + 10) bludgeoning damage. If the target is a creature, it is grappled (escape DC 20). If the target is Huge or smaller, it is also restrained until this grapple ends. While grappling the target, Cthulhu has advantage on attack rolls against it. Cthulhu can grapple a maximum of four creatures at a time. When Cthulhu moves, any Huge or smaller target it is grappling moves with it.

Wing. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 32 (4d10 + 10) bludgeoning damage. The target has to succeed on a DC 20 Strength check or will be knocked prone.

Otherworldly Gaze. A creature of Cthulhu's choice that is within 120 feet of Cthulhu must succeed on a DC 25 Intelligence saving throw, taking 33 (6d10) psychic damage on a failed save, or half as much damage on a successful one.

Eldritch Howl. Cthulhu emits a soul-splintering howl. Each creature in a 60-foot radius around Cthulhu must make a DC 25 Constitution saving throw, taking 33 (6d10) thunder damage on a failed save and being deafened until the end of its next turn, or half as much damage on a successful one. Each creature also has to make a DC 25 Intelligence saving throw, taking 33 (6d10) psychic damage on a failed save, or half as much damage on a successful one. Not being able to hear does not protect against this attack.

Attack. Cthulhu makes one claw attack, one wing attack, or one tentacle attack.

Rage (Costs 2 Actions). Cthulhu uses his Eldritch Howl.

Unspeakable Horror (Costs 3 Actions). Cthulhu consumes the soul of an unconscious creature within 120 feet of it that it can see. The creature dies and cannot be resurrected except via a Wish spell or until Cthulhu chooses to release its soul or until his physical form is destroyed.