Adult tome dragon

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

Meta magic (15 points). The adult tome dragon can use meta magic to use the following effects on spells. 

• Empowered spell: When the tome dragon rolls damage for a spell, they can spend 1 sorcery point to reroll a number of the damage dice up to one time. The tome dragon must use the new rolls.
• Heightened spell: When the tome dragon casts a spell that forces a creature to make a saving throw to resist its effects, they can spend 3 sorcery points to give one target of the spell disadvantage on its first saving throw made against the spell.
• Twinned spell: When the tome dragon casts a spell that targets only one creature and doesn't have a range of self, they can spend a number of sorcery points equal to the spell's level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip). To be eligible for Twinned Spell, a spell must be incapable of targeting more than one creature at the spell's current level.

Innate Spellcasting. The adult tome dragon’s innate spellcasting ability is Wisdom. The adult tome dragon can innately cast the following spells , requiring no material components:

At will: arcane eye

3/day: clairvoyance 

1/day: plane shift

Spellcasting. The Adult tome dragon is a 15th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 18, +10 to hit with spell attacks). The adult tome dragon has following sorcerer spells prepared:
Cantrips (at will): blade ward, control flame, dancing lights, mending, prestidigitation, shocking grasp
1st level (4 slots): detect magic, false life, shield
2nd level (3 slots): crown of madness, mind spike, misty step
3rd level (3 slots): blink, slow
4th level (3 slots): blight, sickening radiance 
5th level (2 slots): dominate person
6th level (1 slots): mental prison 
7th level (1 slots): reverse gravity 
8th level (1 slots): earthquake

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

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., 1 target. Hit: 13 (2d10 + 3) piercing damage. 

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 9 (2d6 + 3) [damage type] damage. 

Tail. Melee Weapon Attack: +8 to hit, reach 15 ft., 1 target. Hit: 11 (2d8 + 3) 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 15 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.

Elemental bead breath (Recharges on 5/6). The adult tome dragon spits out a bead of elemental that goes up to 70ft and lands where the tome dragon wishes it to and explodes in a 15ft by 15ft space and the dragon chooses one of the following damage types: bludgeoning, fire, piercing, thunder. Each creature within the blast radius must make a dc 14 Dexterity save or take 36 (9d8) damage of the chosen damage type. On a successful save a creature takes half damage. 

The adult tome 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 adult tome 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 10 feet of the dragon must succeed on a DC 14 Dexterity saving throw or take 9 (2d6 + 3) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.