Archfey

Improved Magic Resistance. The Archfey has advantage on saving throws against spells and other magical effects and takes half damage from spells.

Shapechanger. The Archfey can use its action to polymorph into a medium, small, or tiny humanoid or fey it has seen, or back to its true form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

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

Magic Weapons. The Archfey's weapon attacks are magical.

Spellcasting. The Archfey is a 20th-level spellcaster. Its spellcasting ability is charisma, spell save DC 24, +17. The Archfey has following spells prepared:
Cantrips (at will): friends, druidcraft, dancing lights, minor illusion, thorn whip, mage hand, vicious mockery, detect magic, speak with animals
1st level (5 slots): animal friendship, charm person, command, disguise self, hex, hideous laughter, sleep, entangle, healing word, sanctuary, faerie fire

2nd level (5 slots): misty step, animal messenger, blur, enthrall, hold person, invisibility, mirror image, suggestion, barkskin, lesser restoration, alter self, healing spirit

3rd level (4 slots): hypnotic pattern, major image, counterspell, dispel magic, bestow curse, conjure animals, clairvoyance, summon fey, plant growth

4th level (4 slots): polymorph, charm monster, compulsion, dominate beast, dimension door,  divination, greater invisibility, hallucinatory terrain, guardian of nature

5th level (3 slots): commune with nature, dominate person, dream, mislead, reincarnate, steel wind strike, tree stride, teleportation circle, greater restoration, mass cure wounds

6th level (3 slots): conjure fey, druid grove, heal, mass suggestion, wall of thorns

7th level (2 slots): project image, teleport

8th level (2 slots): dominate monster, power word stun 

9th level (1 slots): true resurrection, storm of vengeance 

Multiattack. the Archfey can use its Unworldly Presence. it then makes four melee or longbow attacks. 

Longsword. Melee Weapon Attack: +19 to hit, reach 5 ft., one target. Hit: 18 (1d10 + 12) slashing damage. 

Longbow. Ranged Weapon Attack: +19 to hit, range 150/600 ft., one target. Hit: 17 (1d8 + 12) piercing damage.

Unworldly Presence. Each creature of the Archfey's choice that is within 120 ft. of the Archfey and aware of it must succeed on a DC 20 Wisdom saving throw or become Charmed for 1 minute. A creature can repeat this 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 Archfey's Unworldly Presence for the next 24 hours. 

Fey Step: as a bonus action the Archfey may magically teleport up to 60 feet to an unoccupied space they can see.

Parry. The Archfey adds 5 to its AC against one melee attack against it. To do so the Archfey must see the attacker and be wielding a melee weapon.

Enter the description for how legendary actions work for your monster here.

Longbow (Costs 1 Actions). The Archfey makes a longsword attack.

Longsword (Costs 1 Actions). The Archfey makes a longsword attack.

Fey Step (Costs 1 Action). The Archfey uses its Fey Step.

Cast a Spell (Costs 2 Actions). The Archfey casts one of its spells