Alice, Aspect of Tiamat

Draconic Ancestry: Alice has draconic blood, granting her a natural resistance to all elemental damage types (acid, cold, fire, lightning, poison, thunder).

Tiamat's Blessing: Alice's magic is imbued with the power of Tiamat, allowing her to cast spells with a more potent effect. She can cast any spell from the sorcerer spell list as a 17th-level sorcerer.

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

Alice is a 17th-level sorcerer. Her spellcasting ability is Charisma (spell save DC 18, +14 to hit with spell attacks). She has the following sorcerer spells prepared:

Cantrips (at will): Acid Splash, Fire Bolt, Minor Illusion, Message, Prestidigitation, Shocking Grasp

1st Level (4 slots): Charm Person, Disguise Self, Sleep, Tasha's Hideous Laughter

2nd Level (3 slots): Invisibility, Suggestion, Web

3rd Level (3 slots): Fireball, Hypnotic Pattern, Counterspell

4th Level (3 slots): Confusion, Polymorph, Wall of Fire

5th Level (3 slots): Cone of Cold, Hold Monster, Telekinesis

6th Level (2 slots): Chain Lightning, Disintegrate

7th Level (2 slots): Fire Storm, Mirage Arcane

8th Level (1 slot): Mind Blank, Dominate Monster

9th Level (1 slot): Prismatic Wall

Multiattack. Alice makes three attacks: one with her greatsword and one with with her breath weapon.

Greatsword: Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 14 (2d6 + 5) slashing damage.

Breath Weapon (Recharge 5-6): Alice exhales a 30-foot cone of an element of her choice (acid, cold, fire, lightning, poison,). Each creature in the cone must make a DC 18 Dexterity saving throw, taking 30 (8d8) damage of the chosen element on a failed save, or half as much damage on a successful one

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

Legendary Actions: Alice 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. Alice regains spent legendary actions at the start of her turn.

Attack: Alice makes one greatsword attack.

Move: Alice moves up to her speed.

Cast a Spell: Alice casts one spell from her spell list.