Valecia

Intimidate Prey. As an action Valecia can spread her wings revealing a terrifying visage. Anyone within a 150ft cone must make a DC 17 Wisdom Saving throw or be Frightened for 10 minutes.

Elemental Mastery. Valecia can change the damage type to any spell or attack to fire damage.

Spellcasting. Valecia is a 20-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 23, +15 to hit with spell attacks). Valecia has following spells prepared:
Cantrips (at will): Produce Flame, Control Flames, Create Bonfire, Primal Savagery 
1st level (4 slots): Shield, Faerie Fire, Burning Hands, Mage Armor
2nd level (3 slots): Dragon's Breath, Flaming Sphere, Scorching Ray
3rd level (3 slots): Fireball, Flame Arrows, Counterspell
4th level (3 slots): Wall of Fire, Polymorph, Dominate Person
5th level  (3 slots): Immolation, Flame Strike
6th level (2 slots), 7th, 8th, 9th levels (1 slot).

Multiattack. Valecia uses Intimidate Prey then makes one ranged attacks and a spell 

Claw. +12 to hit, reach 5 ft., 1 target. Hit: 28 (7d4 + 10) Slashing damage. 

Flame Bow. +12 to hit, range 120/600 ft., 3 target. Hit: 40 (8d6 + 12) Piercing, Fire damage.

Spellcasting. Valecia cast counterspell at the appropriate level.

Winged Shield. Valecia uses her wings to protect herself, she gains a +12 to AC

Ranged Attack. Flame Bow: +25 to hit, range 120/600 ft., 3 target. Hit: 42 (12d6 + 12) Piercing, Fire damage.

Valecia can take 3 legendary actions, choosing from the options below. Only one legendary action can be used and only at the end of another creature's turn. Valecia regains spent legendary actions at the start of its turn.

Detect. Valecia gains Truesight until the end of her next turn.
Spellcasting. Valecia casts Fireball at 5th level.
Wing Swipe (Costs 2 Actions). Valecia swipes her wings at your feet, any creature in a 10 foot radius of Valecia must succeed on a DC 20 Dexterity saving throw or take 14 (3d8 +10) bludgeoning, fire damage and be knocked prone