Arch-devil Zephyros Nightbinder

Devil’s Sight. Zephyros can see normally in darkness, both magical and nonmagical, to a distance of 120 feet.

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

Magic Resistance. Zephyros has advantage on saving throws against spells and other magical effects.

Magic Weapons. Zephyros’s weapon attacks are magical.

Aura of Whispered Lies. While Zephyros isn’t incapacitated, hostile creatures that start their turn within 30 feet of him must succeed on a DC 23 Wisdom saving throw or be rattled by infernal whispers until the start of their next turn. Affected creatures have disadvantage on Wisdom saving throws, and they can’t gain advantage on attack rolls while they remain in the aura. A creature that succeeds is immune to this aura for 24 hours.

Archdevil of Whispers. When Zephyros deals damage with a spell, he can choose to have that damage become psychic. If he does, the first time the target makes a saving throw against being charmed or frightened by Zephyros before the end of his next turn, the target makes that save with disadvantage.

Mirrorbound Shadows. Zephyros can command inky copies of himself, called Shadows of Nightbinder (CR 3 minions). He can have up to three such shadows existing at any time. If he is reduced to 0 hit points or leaves the plane, all existing Shadows of Nightbinder crumble into black smoke.

Zephyros’s innate spellcasting ability is Charisma (spell save DC 23, +15 to hit with spell attacks). He can innately cast the following spells, requiring no material components:

At will: charm person, command, darkness, detect thoughts, disguise self, minor illusion, suggestion
3/day each: fear, greater invisibility, synaptic static, telekinesis, dimension door
1/day each: dominate monster, feeblemind, power word stun, plane shift (self only), teleport

Multiattack. Zephyros makes three attacks in any combination with Whisperblade or Shadow Lash.

Whisperblade. Melee Weapon Attack: +13 to hit, reach 5 ft., one target.
Hit: 15 (2d8 + 6) slashing damage plus 18 (4d8) psychic damage.
If the target is charmed or frightened, it takes an extra 9 (2d8) psychic damage.

Shadow Lash. Ranged Spell Attack: +15 to hit, range 120 ft., one target.
Hit: 22 (4d10) necrotic damage, and the target must succeed on a DC 23 Wisdom saving throw or be frightened of Zephyros until the start of his next turn.

Word of Binding (Recharge 5–6). Zephyros targets up to three creatures of his choice that he can see within 60 feet. Each target must make a DC 23 Charisma saving throw. On a failure, a creature is charmed by Zephyros and incapacitated, and its speed becomes 0 as invisible chains of oaths and doubt coil around its soul. The effect lasts for 1 minute. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. On a successful initial save, the creature is immune to this ability for 24 hours.

Devouring Whispers (Recharge 6). Zephyros unleashes a wave of soul-gnawing murmurs in a 60-foot cone. Each creature in that area must make a DC 23 Wisdom saving throw, taking 54 (12d8) psychic damage on a failed save, or half as much on a success. A creature that fails the save is also frightened of Zephyros until the end of its next turn and can’t willingly move closer to him.

Shadow Command.
Zephyros targets one Shadow of Nightbinder that he can see within 60 feet. The shadow can immediately use its reaction to move up to its speed and make one Shadow Claw attack.

This basically lets him “direct” a minion each round, tightening the encounter without adding more legendary actions.

Whispered Clause (Recharge 4–6).
Zephyros targets one creature he can see within 30 feet that is charmed or frightened by him. The target must succeed on a DC 23 Wisdom saving throw or take 13 (3d8) psychic damage and be compelled to move up to half its speed to a space of Zephyros’s choosing that it can reach (no opportunity attacks for this movement).
If the target ends this movement within 5 feet of a mirror or other reflective surface, Zephyros has advantage on the next attack roll he makes against it before the end of his next turn.

Infernal Rebuke (3/Day).
When Zephyros takes damage from a creature he can see within 60 feet, he can unleash a burst of hellfire and psychic agony. The creature must make a DC 23 Dexterity saving throw, taking 27 (6d8) damage on a failed save, or half as much on a success.
You can choose the damage as fire, psychic, or half-and-half when you use this reaction.

Twisted Oath.
When a creature Zephyros can see within 60 feet succeeds on a saving throw against being charmed or frightened by him, he can twist the remnants of that effect. The creature must immediately make a second Wisdom saving throw against DC 23:

• On a failed second save, the creature takes 10 (3d6) psychic damage and has disadvantage on its next attack roll or saving throw before the end of its next turn.

• On a success, nothing else happens; the creature shrugs off the last of his influence.

Mirror Interposition.
When Zephyros is hit by an attack while he is within 5 feet of a mirror or other reflective surface at least Medium-sized, he can use his reaction to step partway into the reflection. The attack roll is rerolled with disadvantage.

• If the attack still hits, he takes half the damage from that attack.

• If the attack misses, Zephyros can teleport up to 15 feet to an unoccupied space adjacent to another mirror or reflective surface he can see.

Zephyros 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. Zephyros regains spent legendary actions at the start of his turn.

Whisper Step. Zephyros magically teleports up to 30 feet to an unoccupied space he can see.

Shadow Strike. Zephyros makes one Whisperblade or Shadow Lash attack.

Tempting Murmur (Costs 2 Actions). Zephyros targets one creature he can see within 60 feet. The target must succeed on a DC 23 Wisdom saving throw or be charmed by him until the end of its next turn. While charmed in this way, the creature treats Zephyros as a trusted ally: Zephyros has advantage on attack rolls against the creature, and the creature has disadvantage on saving throws against Zephyros’s spells and abilities.

Twist the Knife (Costs 3 Actions). Zephyros chooses a creature he can see that is charmed or frightened by him. The creature immediately takes 18 (4d8) psychic damage and must succeed on a DC 23 Wisdom saving throw or be stunned until the start of Zephyros’s next turn.

Summon Shadow (Costs 3 Actions). Zephyros targets a mirror or other reflective surface he can see within 60 feet that is at least Medium-sized. A Shadow of Nightbinder (your CR 3 minion stat block) claws its way out of the reflection into an unoccupied space adjacent to that surface and acts on the next initiative count 20. Zephyros can’t have more than threeShadows of Nightbinder summoned by this feature at one time.

Mirrorheart of the Archdevil (Mythic, 1/Day).
The first time Zephyros would be reduced to 0 hit points, he instead shatters into inky fragments and is pulled into the nearest mirror or reflective surface within 60 feet.

• His hit points reset to 170.

• All conditions affecting him end.

• Creatures of his choice within 20 feet of that mirror must succeed on a DC 23 Wisdom saving throw or take 27 (6d8) psychic damage and be frightened of Zephyros until the end of their next turn (half damage and not frightened on a success).

• Zephyros reappears in an unoccupied space within 10 feet of that mirror, wreathed in writhing shadows.