Corrector

Legendary Resistance (8/Day). If the Corrector fails a saving throw, it can choose to succeed instead.

Mythic Presence. Regardless of Intelligence score, even non-sentient creatures recognize the Corrector as a being of immense, otherworldly power. 

Prescient. The Corrector cannot be surprised.

Fire Absorption. Whenever the Corrector is subjected to fire damage, it takes no damage and instead regains a number of hit points equal to the fire damage dealt.

Inscrutable. The Corrector is immune to any effect that would sense its emotions or read its thoughts, as well as any Divination spell that it refuses.

Immutable Form. The Corrector is immune to any spell or effect that would alter its form.

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

Incorruptible Conviction. The Corrector automatically succeeds Charisma saving throws.

Magic Weapons. The Corrector's weapon attacks are magical.

Spellcasting. The Corrector harnesses the cosmic energy of the universe to cast spells. The Corrector recovers all of its spell slots at dawn. It can cast the following spells innately (spell save DC 25, +15 to hit with spell attacks):

At will: counterspell (5th level), geas (5th level), telekinesis, disintegrate (8th level), forcecage, plane shift, antimagic field, feeblemind

8/day: gate, imprisonment, power word kill, prismatic wall, time stop, true resurrection 

Multiattack. The Corrector makes four melee attacks.

Blade Arm. Melee Attack: +13 to hit, reach 15 ft., one target. Hit: 69 (9d10 + 21) piercing or slashing damage, Corrector's choice.

Crushing Grip. Melee Attack: +13 to hit, reach 10 ft., one target. Hit on a target medium or smaller: The Corrector crushes the target beyond recovery, killing it instantly. Hit on a target large or larger: 46 (6d10 + 14) bludgeoning damage.

Life Drain (Recharge 4-6). The Corrector unleashes necrotic energy in a 20-foot radius around itself. Each creature in that area must make a DC 25 Constitution saving throw, taking 45 (10d8) necrotic damage on a failed save, or half as much damage on a successful one. 

Force Blast (Recharge 5-6). The Corrector fires a blast of pure force from the center of its chest at a singe target. The target must make a DC 25 Strength saving throw, taking 135 (30d8) force damage and getting knocked prone on a failed save, or half as much damage on a successful one. 

The Corrector 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. The Corrector regains spent legendary actions at the start of its turn.

Blade Arm Attack. The Corrector makes an attack with its blade arm.

Teleport. The Corrector teleports anywhere up to 90 ft. away from its current location.

Battlefield Recovery. The Corrector recovers 30 hit points.

The Corrector is a mythic being, commanding power beyond that of even the strongest legendary creatures. It is, in essence, an extension of the will of the universe; as such, it can take actions that bend the rules of reality itself. 

Restore Order. In an emergency, the Corrector can take drastic action to restore the universe to balance after a sufficiently harmful disruption. Thrice per day, the Corrector may cast the spell Wish. Due to the Corrector's nature, it cannot act against the interest of the universe; as such, it faces none of the usual consequences of casting the spell. This is considered an option of last resort.

Time-Space Rupture. Once per day, the Corrector can create a tear in the fabric of reality. Four creatures of its choice within its line of sight must make a DC 27 Charisma saving throw. On a successful save, nothing happens to the creature. On a failed save, the Corrector transports the creature, willingly or unwillingly, instantly to a precise location of the Corrector's choice on any plane of the Corrector's choice. This is considered an option of last resort.

Absolute Execration. After killing its target or any other creature that is neither a bystander nor an innocent, the Corrector may suck the creature's soul into its chest and erase it from existence irrecoverably. In effect, this erases the creature's identity from the universe. There is no appeal.