Boon of Immortality. Iggwilv is immune to any effect that would age her, and she can’t die from old age.

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

Magic Resistance. Iggwilv has advantage on saving throws against spells and other magical effects. (This trait is bestowed by her robe of the archmagi.)

Special Equipment. Iggwilv wears an amulet of the planes and a robe of the archmagi.

Multiattack. Iggwilv makes two mind whip attacks and then casts a spell or uses abyssal rift.

Mind whip. The target must must succeed on a DC 22 Intelligence saving throw. On a failed save, the target takes  24 (7d6) psychic damage, and it can’t take a reaction until the end of its next turn. Moreover, on its next turn, it must choose whether it gets a move, an action, or a bonus action; it gets only one of the three. On a successful save, the target takes half as much damage and suffers none of mind whip's other effects.

Abyssal Rift (Recharge 5–6). Iggwilv opens a momentary Abyssal rift within 120 feet of her. The rift is a 20-foot-radius sphere. Each creature in that area must make a DC 22 Constitution saving throw, taking 40 (9d8) necrotic damage on a failed save, or half as much damage on a successful one. In addition, there is a 50 percent chance that 3 hezrous then appear in unoccupied spaces in the sphere. They act as Iggwilv’s allies, take their turns immediately after hers, and can’t summon other demons. They remain until they die or until Iggwilv dismisses them as an action.

Spellcasting. Iggwilv casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 24, +16 to hit with spell attacks):

At will: detect magic, disguise self, invisibility, light, mage hand, message, prestidigitation, Tasha’s hideous laughter, dispel magic

3/day each:  fireball

1/day each: telekinesis, teleport, wish

Fiendish Step. Iggwilv teleports, along with any equipment she is wearing or carrying, to an unoccupied space she can see within 30 feet of her. Each creature within 10 feet of the space she left must make a Dexterity saving throw, taking 15 (7d6) fire damage on a failed save, or half as much damage on a successful one.

Dread Counterspell. Iggwilv utters a dread word to interrupt a creature she can see that is casting a spell. If the spell is 4th level or lower, it fails and has no effect. If the spell is 5th level or higher, Iggwilv makes an Intelligence check (DC 10 + the spell’s level). On a success, the spell fails and has no effect. Whatever the spell’s level, the caster takes 10 (3d6) psychic damage if the spell fails.

Iggwilv 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. Iggwilv regains spent legendary actions at the start of her turn.

Witchcraft. Iggwilv casts an at will spell or uses Fiendish step.

Dark Speech (Costs 2 Actions). Iggwilv utters a phrase in a forbidden language and targets one or two creatures she can see within 60 feet of her. Each target must succeed on a DC 22 Wisdom saving throw or take 11 (2d10) psychic damage and be frightened of Iggwilv for 1 minute. A target can repeat the save at the end of each of its turns, ending the effect on itself on a success and thereby becoming immune to Iggwilv’s Dark Speech for 24 hours.