Circe

Nymph Companion (Mythic Feature). Circe is linked with a Nymph Companion. As a bonus action, Circe can call this companion to her from any distance, so long as they are on the same plane of existence as each other.

Magic Resistance. Circe has advantage on saving throws against spells and other magical effects.

Legendary Resistance (3/Day). If Circe fails a saving throw, she can choose to succeed on that saving throw instead.

Master of Transmutation. Whenever Circe casts a transmutation spell that targets exactly one creature other than herself, that spell instead targets 1d4 creatures.

Uncultured Swine. Male humanoid creatures have disadvantage on saving throws against transmutation spells cast by Circe.

Spellcasting. Circe is a 20th-level spellcaster. Her spellcasting ability is Charisma (spell save DC 19, +11 to hit with spell attacks). Circe has following spells prepared:

Cantrips (at will): dancing lights, fire bolt, mage hand, prestidigitation, shocking grasp, vicious mockery

1st level (4 slots): detect magic, expeditious retreat, identify, Tasha's hideous laughter, unseen servant

2nd level (3 slots): detect thoughts, enlarge/reduce, skywrite

3rd level (3 slots): counterspell, fireball, sending

4th level (3 slots): compulsion, conjure woodland beings, dimension door, polymorph

5th level (3 slots): animate objects, modify memory, scrying, telekinesis

6th level (2 slots): mass suggestion, true seeing

7th level (2 slots): forcecage, teleport

8th level (1 slot): animal shapes, glibness

9th level (1 slot): true polymorph

Chill Touch. Ranged Spell Attack: +11 to hit, range 120 ft., one target. Hit: 18 (4d8) necrotic damage and it can't regain hit points until the start of Circe's next turn.

Lightning Lure. Circe targets one creature it can see within 15 feet of her. The target must succeed on a DC 19 Strength saving throw or be pulled up to 10 feet in a straight line towards her and take 18 (4d8) lightning damage if it is within 5 feet of you.

Sunblade. Melee or Ranged Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 10 (1d8 + 6) radiant damage. If the target is undead, that target takes an extra 4 (1d8) radiant damage.

Booming Blade. Circe makes a melee attack with her sunblade against one creature within 5 feet of her. On a hit, the target suffers the weapon attack's normal effects, takes an extra 13 (3d8) thunder damage, and becomes sheathed in booming energy until the start of her next turn. If the target willingly moves 5 feet or more before then, the target takes 18 (4d8) thunder damage and the spell ends.

Green-Flame Blade. Circe makes a melee attack with her sunblade against one creature within 5 feet of her. On a hit, the target suffers the weapon attack's normal effects, takes an extra 13 (3d8) fire damage, and green fire leaps from the target to a different creature of her choice that she can see within 5 feet of it. The second creature takes 19 (3d8+6) fire damage.

Alluring Song (Recharge 5–6).  Circe begins to sing an enchanting melody. She targets one creature that she can see within 90 feet of her. If the target can hear Circe, it must succeed on a DC 17 Wisdom saving throw or be magically charmed. The charmed creature regards Circe as a trusted friend to be heeded and protected, and it has disadvantage on saves against her transmutation spells. If Circe is attacked, charmed creatures will act in her defense. 

Each time Circe or her allies do anything harmful to the target, it can repeat the saving throw, ending the effect on itself on a success. Otherwise, the effect lasts 24 hours or until Circe is incapacitated, is on a different plane of existence from the target or ends the effect as a bonus action. 

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

Cantrip. Circe casts one of her available cantrips.

Coordinated Assault (Costs 2 Actions). Circe attacks with a melee cantrip, and then its mount can use its reaction to make a melee weapon attack.

Shrink (Costs 2 Actions). Circe casts enlarge/reduce choosing the reduce effect, using a spell slot as normal.

Filthy Swine (Costs 3 Actions). Circe casts polymorph transforming the target into a boar, using a spell slot as normal.

When Circe's Nymph Companion is killed, she immediately gains 100 temporary hit points and transforms similar to casting the Tasha's otherworldly guise spell as a mythic action  (no concentration needed), gaining the following effects:

• Her resistances to radiant and necrotic damage turn into immunities. 
• Spectral wings appear on her back, giving her a flight speed of 40 feet. 
• Her AC increases to 18.
• Her weapon attacks become magical and she can now use her spellcasting ability modifier instead of her dexterity (see below). 
• She gains Multiattack. Circe may make two Sunblade attacks, one of which may act as the somatic component of a melee cantrip. 

Sunblade. Melee or Ranged Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 12 (1d8 + 8) radiant damage. If the target is undead, that target takes an extra 4 (1d8) radiant damage.