boon of Immortality. Zybilna is immune to any effect that would age her, and she can't die from old age.

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

Spellcasting. Zybilna 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.

3/day each: dispel magic, fly, polymorph

1/day each: maze, telekinesis, teleport, wish.

Abyssal Reference. You can reference the Demonomicon whenever you make an Intelligence check to discern information about demons or a Wisdom (Survival) check related to the Abyss. When you do so, you can add double your proficiency bonus to the check.

Fiendish Scourging. Your magic causes pain to fiends. While carrying the book, when you make a damage roll for a spell you cast against a fiend, you use the maximum possible result instead of rolling.

Ensnarement. While carrying the book, whenever you cast the magic circle spell naming only fiends, or the planar binding spell targeting a fiend, the spell is cast at 9th level, regardless of what level spell slot you used, if any. Additionally, the fiend has disadvantage on its saving throw against the spell.

Demonomicon Spellcasting. The book has 8 charges. It regains 1d8 expended charges daily at dawn. While holding it, you can use an action to cast Tasha's hideous laughter from it or to expend 1 or more of its charges to cast one of the following spells (save DC 20) from it: magic circle (1 charge), magic jar (3 charges), planar ally (3 charges), planar binding (2 charges), plane shift (to layers of the Abyss only; 3 charges), summon fiend (3 charges).

Crook Spellcasting. The crook has 6 charges. While holding it, you can use an action to expend 1 or more of its charges to cast one of the following spells (save DC 18) from it: aura of life (2 charges), aura of purity (2 charges), banishment (1 charge), beacon of hope (1 charge), mass cure wounds (3 charges). The crook regains 1d6 expended charges daily at dawn.

Absolute Banishment. While you are attuned to the crook of rao and holding it, you can spend 10 minutes to banish all but the mightiest fiends within 1 mile of you. Any fiend with a challenge rating of 19 or higher is unaffected. Each banished fiend is sent back to its home plane and can't return to the plane the Crook of Rao banished it from for 100 years.

Multiattack. Zybilna makes two Bewitching Bolt attacks.

Bewitching Bolt. Melee or Ranged Spell Attack: +16 to hit, reach 5 ft. or range 120 ft., one target. Hit: 25 (5d6 + 8) lightning damage, and if the target is a creature, it must succeed on a DC 22 Wisdom saving throw or be charmed by Zybilna until the start of her next turn.

Abyssal Rift (Recharge 5–6). Zybilna 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 Zybilna's allies, take their turns immediately after hers, and can't summon other demons. They remain until they die or until Zybilna dismisses them as an action.

Baba Yaga's pestle. melee weapon attack: +3 to hit, reach 5ft., one target. Hit: 3 (1d6) bludgeoning. The pestle has 12 charges. When you hit with a melee attack using the pestle, you can expend up to 3 of its charges to deal an extra 4 (1d8) force damage for each charge expended. The pestle regains all expended charges daily at dawn.