Amethyst Dragon Abomination

Legendary Resistance (5/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Immunity to any spells that might alter it's form. 

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +16 to hit, reach 15 ft., one target. Hit: 18 (2d10 + 8) piercing damage.

Claw. Melee Weapon Attack: +16 to hit, reach 10 ft., one target. Hit: 17 (2d8 + 8) slashing damage.

Tail. Melee Weapon Attack: +16 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Frightful Presence. Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 23 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 the dragon's Frightful Presence for the next 24 hours.

Breath Weapons (Recharge 4–6). The dragon uses one of the following breath weapons.

Force Breath. The dragon exhales pure magical force in an 60-foot line that is 15 feet wide. Each creature in that line must make a DC 19 Intelligence saving throw, taking 80 (15d10) force damage on a failed save, or half as much damage on a successful one.

Blinding Breath. The dragon exhales fine particles of dust in a 25-foot cone. Each creature in that area must succeed on a DC 22 Constitution saving throw or become blinded for 5 minutes. This effect ends for a creature if the creature succeeds on a DC 22 Wisdom saving throw or if the blindness is cured, magical or otherwise.

Spellcasting (Psionics). The dragon casts one of the following spells, at it's highest available level, requiring no spell components and using wisdom as the spellcasting ability (spell save DC 24, +16 to hit with spell attacks):

5/day each: Blink, Levitate, Dispel Magic, Freedom of Movement, Globe of Invulnerability, Plane Shift, Protection from Evil and Good, Sending, Counterspell

3/day each: Power word kill, Time Stop, Flesh to Stone, Harm, Heal

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.

Invisibility. The dragon turns invisible for 2 rounds, as if using the invisible spell.

The dragon can take 6 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.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 15 feet of the dragon must succeed on a DC 25 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.

Psionics (Costs 2 Actions). The dragon uses Psychic Step or Spellcasting.

Explosive Crystal (Costs 3 Actions). The dragon spits an amethyst that that explodes at a point it can see within 60 feet of it. Each creature within a 20-foot-radius sphere centered on that point must succeed on a DC 23 Dexterity saving throw or take 18 (4d8) force damage and be knocked prone.