Living Void (Recharges after a Short or Long Rest). If Zexara would be reduced to 0 hit points, her current hit point total instead resets to 250 hit points, and she regains the use of her breath weapon. Additionally, Zexara can now use the options in the "Mythic Actions" section for 1 hour. Award a party an additional 50,000 XP (100,000 XP total) for defeating Zexara after her Living Void activates. When this trait becomes active her physical form becomes that of a living shadow like sludge that reeks of death and decay and gains the Amorphous trait as seen in the black pudding statblock.

Aura of Gloom. Zexara is surrounded in an aura of gloom and shadows. The aura reduces any bright light in a 30-foot radius around Zexara to dim light. Whenever an enemy that is frightened Zexara starts its turn in the aura, it takes 22 (4d10) psychic damage. Additionally, Zexara and creatures she chooses in the aura are draped in deeper shadow. Creatures that rely on sight have disadvantage on attack rolls against creatures draped in this shadow.

Aura of Hatred. Zexara, as well any fiends and undead of her choice within 30 feet of her, gains a bonus to melee weapon damage rolls equal to Zexara’s Charisma modifier.

Innate Spellcasting. Zexara’s spellcasting ability is Charisma (spell save DC 24, +16 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: spirit shroud, detect magic, chill touch (17th level), Arms of Hadar (2nd level)

3/day each: dispel magic, hellish rebuke, create undead

2/day each: blight, destructive wave, Bestow curse (5th level)

1/day each: time stop, maddening darkness

Legendary Resistance (3/Day). If Zexara fails a saving throw, she can choose to succeed instead. Zexara also has advantage on saving throws against spells and other magical effects.

Magic Weapons. Zexaras weapon attacks are magical.

Sunlight Sensitivity. While in sunlight, Zexara has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Demonic Smite. When Zexara hits with a melee weapon attack, they deal an additional 5(1d10) necrotic damage to the target (included in the attack).

Master of Undeath. When Zexara casts animate dead or create undead, she chooses the level at which the spell is cast, and the creatures created by the spells remain under his control indefinitely. Additionally, she can cast create undead even when it isn’t night.

Unusual Nature. Zexara doesn't require food, drink, or air.

Queen of Living Shadow. While in dim light or darkness, Zexara has resistance to damage that isn’t force, psychic, or radiant. Also, while in dim light or darkness, Zexara can take the Hide action as a bonus action.

Multiattack. Zexara makes two Bone Blade attacks and can use her Dreadful Presence.

Bone Blade. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (1d10 + 8) slashing damage plus 5 (1d10) necrotic damage.

Dreadful Presence. Each creature of Zexara's choice that is within 120 feet of her and aware of her must succeed on a DC 24 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it.

Acid Breath (Once per Day). Zexara exhales acid in a 15-­foot line that is 5 feet wide. Each creature in that line must make a DC 15 Dexterity saving throw, taking 36 (8d8) acid damage on a failed save, or half as much damage on a successful one.

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

Lashing Shadows. Zexara casts Arms of Hadar (2nd level).

Acid Breath. Zexara uses her acid breath

Creeping Death (Costs 2 Actions). Zexara chooses a point on the ground that she can see within 100 feet of her. A cylinder of swirling necrotic energy 60 feet tall and with a 10-foot radius rises from that point and lasts until the end of Zexara’s next turn. Creatures in that area are vulnerable to necrotic damage.

If Zexara's Living Void trait has activated in the last hour, it can use the options below as legendary actions.

Destructive Void (Costs 3 actions).  Zexara conjures a singularity of darkness and destructive force as if by the effect of the Ravenous Void, this effect functions as that spell.

Shadow Strike. Melee Spell Attack: +16 to hit, reach 10 ft., one target. Hit: 24 (3d10 + 8) necrotic damage.