Cosmic Void

Legendary Resistance (10/Day). If the Deep fails a saving throw, he can choose to succeed instead.

Cosmic Armor. The Cosmic Void cannot be dealt damage by anything that deals less than 10 damage.

Eternal. The Cosmic deep doesn't age, cannot die and will exist for all eternity. If slain, the Cosmic Deep will return to it's resting place and slumber until awakened.

Cosmic Horror. The Cosmic Void doesn’t require air, food, drink, or sleep and all creatures it devours becomes part of its biomass.

The Ancient Forces You Draw Upon Mean Nothing To One As Old As The Universe. The Cosmic Deep is immune to Almighty Damage and is resistant to all.

 You Are Not Unlike An Ant Fighting The Sun. Every Melee attack the Cosmic Deep does, targets 500 ft. Centered around the target.

Only the Ultimate Nullifier Would Give Me Pause. The Cosmic Deep doesn't spend spell slots when using magic and cannot get exhausted.

Multiattack. The Cosmic Deep does 2 Pangea and 1 Supernova Slam.

Pangea. Melee unnarmed Attack: +20 to hit, reach 50 ft., one target. Hit: 10 (10d10 + 10) bludgeoning damage.

Supernova Slam. Melee unnarmed Attack: +20 to hit, reach 100 ft., one target. Hit: 10 (10d10 + 10) fire and bludgeoning damage.

Andromeda (Recharge 3–4). The Cosmic Deep conjures a torrent of corrupted cosmic energy that fill a 300-foot cone and pass through all creatures in that area before dissipating. Each creature in that area must make a DC 27 Constitution saving throw. On a failed save, the creature takes 100 (10d20) necrotic damage and gains one level of exhaustion.

Galaxy Breaker. The Cosmic Deep causes Cosmic Energy to engulf one creature he can see within 500 feet of itself. The target must make a DC 25 dexterity saving throw or take 200 necrotic and 200 radiant damage. If a creature dies by this attack it becomes a herald of the Cosmic Deep or part of the Cosmic Deep's biomass.

Spellcasting.  The Cosmic Void casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 28):

At will: animate dead (as an action), detect magic, dispel magic, fly, lightning bolt, mage hand, prestidigitation, [/spell]dimension door[/spell], scrying, dominate monster, globe of invulnerability, power word kill

Call Herald. The Cosmic Deep summons any remaining living hearalds to assist it in battle.

The Cosmic Deep has 5 reactions.

Devour. Whenever the Cosmic Void is dealt Almighty damage it can gains hit points, equal to the damage of the attack.

 You Are Like An Amoeba To Me. The Cosmic Deep gains immunity to one attack this reaction costs 2 reactions.

Gravitational Pull. Target creature must make a strength saving of 28 or higher or be pulled 200 ft. Near the Cosmic Deep. If a creature is 10 ft. Near to the Cosmic Deep after the gravitational pull, the creature must make a strength saving throw of 30 or higher or be dealt 50 damage and pushed 1,000 ft. into the air, away from the Cosmic Deep.

The Cosmic Void can take 5 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 Cosmic Void regains spent legendary actions at the start of its turn.

Detect. The Cosmic Void makes a successful Wisdom (Perception) check.

Spell Attack. The Devourer of the Deep casts a spell.

Oxygen Crush. The Cosmic Deep pulls target creature's Oxygen it sees 40 ft. near it and if the creature fails a constitution saving throw of 25 or higher it gains one level of exhaustion.

Cosmic Disease. Target creature must make a constitution saving of 20 or higher or be inflicted every condition.