Armageddon, Reaver of Oblivion- Juvenile

Age Old Magic The Armageddon, Reaver of Oblivion is a 3rd-level spellcaster. Its spellcasting ability is WIS (spell save DC 12, +4 to hit with spell attacks). The Armageddon, Reaver of Oblivion has all spellcasting spells prepared(due to its age):
Cantrips (at will): all cantrips

1st level (15 slots): all first level spells

2nd level (10 slots): all second level spells

3rd level (5 slots): all third level spells

Uncanny Senses. Armageddon can’t be surprised unless it’s incapacitated.

Sense Magic. Armageddon senses magic within 200 feet of it at will. This trait otherwise works like the detect magic spell but isn’t itself magical.

Unknowing Aura

Creatures within 120 feet of the creature are not considered proficient with any skills.

multiattack: 3 actions per turn, in any order, must follow size restrictions, except for celestials dragon breath can only be used once per turn.

in any form:

celestial dragons breath (5 times per long rest). You can use your action to exhale destructive energy. When you use your breath weapon, each creature in a 50 ft. cone must make a  WIS saving throw, The DC for this saving throw is 12. if failed creature takes 6d6 psychic damage, if succeeded it takes half as much.

in large or bigger form:

Spiked tongue: roll 4d8+8 piercing damage upon hit as well as 7d4 slashing damage as the tongue grapples you(DC: 15 strength saving throw to escape), slowly crushing you, making you take 2d10 bludgeoning damage per turn your grappled

Slam(melee weapon attack) +8 to hit, 3d12+8 (36) bludgeoning damage 10 ft. reach, charge attack

Stomp(melee weapon attack) +8 to hit 2d12+8(24) bludgeoning damage 5 ft. reach

Bite(melee weapon attack) +8 to hit 2d6+8(12) piercing damage 5 ft. reach

Tail slam(melee weapon attack) +8 to hit4d8+8 bludgeoning damage 15 ft. reach

Disengage- As a bonus action Armageddon can travel its movement speed without provoking an opportunity attack

Dash- As a bonus action Armageddon can travel its movement speed.

Shield. As a reaction to an attack Armageddon may cast shield as a reaction and increase its AC by +5 against that attack.

legendary actions can be used at any size

Legendary Resistance (3/Day). If the celestial fails a saving throw, it can choose to succeed instead.

Legendary shield (2/day): casts shield as a ninth level spell negating all damage unless attacker rolls a D20 and gets at least a 25.

 Grasp of the Void (2/day): The reaver pulls one large or smaller creature up to 30 feet closer to an unoccupied space adjacent to the reaver.

Rending Shockwave (3/day): The reaver slams the ground. Each creature within 15 feet must make a DC 22 Dexterity saving throw or take 18 (4d8) force damage and fall prone.

mythic actions can only be used once enraged healing is activated.

Unattune (3/Day)

When armaggedon hits a creature, that creature loses attunement to one of their magic items.

Void Shield(costs 1 action): At the start of its turn, it gains 100 temporary hit points. This shield reflects force and radiant damage back to the attacker.

Shatter Timeline (costs 2 actions): Target one creature. That creature blinks out of existence until the end of its next turn. It takes 35 (10d6) psychic damage upon return.

Oblivion Step (Costs 2 Actions): The reaver teleports up to 120 feet. It leaves a trail of dead space in its wake. Any creature in that line must make a DC 26 Dexterity saving throw or take 44 (8d10) necrotic damage.

invisibility: as a bonus action it casts ninth level invisibility on itself when severely wounded and out of options and needs to escape, DC: 25 perception check to see it