Vallatrix's Simulacrum

Contingency. When the simulacrum is reduced below half her hit point maximum, invisibility is automatically cast on herself.

Spell Casting. The Simulacrum is a 15th-level Spellcaster. Her spellcasting ability is Intelligence (spell save DC 19, +11 to hit with spell attacks). She has the following wizard spells prepared.

Cantrips (at will): mage hand, minor illusion, ray of frost
1st Level (4 slots): detect magic, magic missile, shield, thunderwave
2nd Level (3 slots): detect thoughts, invisibility, suggestion, mirror image
3rd Level (2 slots):  dispel magic
4th Level (1 slot): ice storm
5th Level (1 slot): cone of cold

Multiattack. The Simulacrum makes three attacks: one with her bite and two with her claws.

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 7 (2d6) fire damage.

Claw. Melee Weapon Attack: +14 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Ice Breath (Recharge 5–6). The Simulacrum exhales bitter cold in a 60-foot cone. Each creature in that area must make a DC 21 Dexterity saving throw, taking 63 (18d6) cold damage on a failed save, or half as much damage on a successful one.