Corrupted Ancient Dragon

Shadow Mage. When the Corrupted Dragon Wyrmling casts a spell they cast it without any somatic or verbal components.

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

Innate Spellcasting. The Corrupted Dragon Wyrmling is a 20-level spellcaster. Its spellcasting ability is Constitution (spell save DC 21, +14 to hit with spell attacks). The Corrupted Dragon Wyrmling has following spells prepared:

Cantrips (at will): Encode Thoughts, Mind sliver, Friends, Message, Prestidigitation.

1st level (4 slots): Catapult, Charm Person, Command, Shield.

2nd level (3 slots): Knock, Suggestion, Arcanist's Magic Aura.

3rd level (3 slots): Fly, Fear, Counter Spell.

4th level (3 slots): Dominate Beast, Charm Monster, Hallucinatory Terrain.

5th level (3 slots): Dominate Person, Telekinesis, Geas.

6th level (2 slots): Mass Suggestion, Investiture of Wind.

 7th level (2 slots): Power Word Pain, Project Image.

8th level (1 slots): Feeblemind.

9th level (1 slots): Psychic Scream.

Multiattack. The dragon can makes three attacks: one with its bite and two with its claws.

Bite. Melee Attack: +14 to hit, reach 5ft., one creature. Hit:  (2d10+5) Piecing damage.

Claws. Melee Attack: +14 to hit, reach 5ft., one creature. Hit:  (2d6+5) slashing damage.

Tail. Melee Attack: +14 to hit, reach 5ft., one creature. Hit:  (2d8+5) Bludgeoning damage.

Shadow Breath (Recharge 5–6). The dragon exhales Black flames in a 90-­foot cone. Each creature in that cone must make a DC 21 Dexterity saving throw, taking 60 (14d10) necrotic damage on a failed save, or half as much damage on a successful one.

Change Shape. The dragon 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. Any equipment it is wearing or carrying is absorbed or borne by the new form (the dragon's choice).

In a new form, the dragon 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 that form.

Magic incarnate. the Corrupted Young Dragon can cast a level 1 spell or lower As a bonus action.

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

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Magic Genius (Costs 2 Actions). the dragon casts a spell of level 4 or lower.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.