Adult Harpy Dragon

Amphibious. Can breath air and water when in Dragon form.

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

Unearthly Grace. The dragon applies her Charisma modifier to all of her saving throws in place of the normal ability modifier.

Spellcasting. The dragon is a 14th-level spellcaster when in Harpy form. Its spellcasting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). The dragon has the following spells prepared:

Cantrips (at will): message, minor illusion , vicious mockery, friends

1st Level (4 slots): silent image, dissonant whispers, sleep, charm person

2nd Level (3 slots): calm emotions, phantasmal force, suggestion, detect thoughts

3rd Level (3 slots): enemies abound, dispel magic, hypnotic pattern

4th Level (3 slots): dimension door, greater invisibility

5th Level (2 slots): synaptic static, dominate person

6th Level (1 slot): guards and wards

7th Level (1 slot): teleport, regenerate

Multiattack. The dragon can use its Frightful presence. It then makes three attacks: one with its bite and two with its claws in dragon form, or two claw attacks when in harpy form.

Bite. Melee Weapon Attack: +10 to hit, reach 10ft., one target. Hit: 18 (2d12 + 5) piercing damage plus 3 (1d6) force damage.

Claw. Melee Weapon Attack: +10 to hit, reach 5ft., one target. Hit: 14 (2d8 + 5) slashing damage.

Tail. Melee Weapon Attack: +10 to hit, reach 10ft., one target. Hit: 16 (2d10 + 5) 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 16 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 effects ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

Baleful Roar [Dragon Form] (Recharge 5-6). The dragon releases a deep bellowing roar. Each creature within a 60 foot radius must make a DC 18 Charisma saving throw or become stunned until the end of its next turn, also taking 50 (10d10) psychic damage on a failed save, or half as much on a successful one.

Change Shape. The dragon magically polymorphs into the form of a humanoid female. Any equipment it is wearing or carrying is absorbed or borne by the new form (the dragon's choice).The dragon gains spell slots equivalent to it's CR rating in level.
When the dragon returns to its dragon form, any gear it carried or wore while in its other form melds into its dragon form but is not considered to be worn or wielded.

Luring Song [Harpy Form]. The harpy sings a magical melody. Every humanoid and giant within 300 feet of the harpy that can hear the song must succeed on a DC 18 Wisdom saving throw or be charmed until the song ends. The harpy must take a bonus action on its subsequent turns to continue singing. It can stop singing at any time. The song ends if the harpy is incapacitated.
While charmed by the harpy, a target is incapacitated and ignores the songs of other harpies. If the charmed target is more than 5 feet away from the harpy, the target must move on its turn toward the harpy by the most direct route, trying to get within 5 feet. It doesn't avoid opportunity attacks, but before moving into damaging terrain, such as lava or a pit, and whenever it takes damage from a source other than the harpy, the target can repeat its saving throw. A charmed target can also repeat the saving throw at the end of each of its turns. If the saving throw is successful, the effect ends on it.
A target that successfully saves against two individual songs is immune to this harpy's song for the next 24 hours.

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.

Claws. The dragon makes a claw attack.

Tail Attack [Dragon Form]. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.