Innate spellcasting: Neifion's spellcasting ability is charisma. He can cast the following spells, requiring no material components. His spell save DC is 24, +12 to spell attacks.

At will: Charm person, Detect magic, Disguise self, Feather fall, Silent image, Polymorph (self, bat form only)

3/day: Blur, Counterspell, Darkness, Dispel magic, Haste

1/day: Blight, Dimension door, Greater invisibility, True seeing

Spell master: Neifion can keep concentration on up to 2 concentration spells at once. However, while doing this he has dissadvantage on concentration checks. If he loses his concentration, he only loses concentration on 1 of the spells. 

Legendary resistance: 3/day: When Neifion fails a saving throw, he can choose to succeed instead.

Magic resistance: Neifion has advantage on saving throws against magic. 

Magic weapons: Neifion's melee weapon attacks are magical. 

Shadow form: While in darkness, Neifion is always treated as if it had half cover. 

Multiattack: Neifion makes two claw attacks and one bite attack attack.

Claw: Melee weapon attack: +14 to hit: Reach 10 ft., One target, hit: The creature takes (4d8+ 8) slashing damage. The creature must also make a DC 24 charisma saving throw or become blinded until the end of its next turn. If the target is already blinded the hit is a critical hit and the target takes an extra (3d8+ 2) slashing damage. 

Bite: Melee weapon attack: +14 to hit: Reach 10 ft., One target, hit: The creature takes (5d6+ 5) piercing damage and if it is blinded it must succeed on a DC 24 charisma saving throw or lose its concentration if it is concentrating on a spell. If it is not concentrating on a spell, it instead loses its attunement to 1 magic item of the targets choice. If it is not attuned to any magic items, it is blinded for 1 minute instead of the normal duration of the blindness. 

Archfey presence: Recharge 6: All creatures within a 60 ft. cube originating from Neifion must succeed on a DC 20 wisdom saving throw or become charmed or afraid of Neifion (his choice) for 1 minute. Neifion has advantage on attacks against any charmed creature and any hit against a charmed creature is a critical hit. Once a creature suffers a critical hit in this way, it is no longer charmed by Neifion. A creature that is afraid of Neifion is always treated as if it is blinded against Neifion's effects and has disadvantage on saving throws against Neifion. Once it fails a saving throw against Neifion, it is no longer afraid of him. A creature that succeeds on a saving throw against this effect has advantage on saving throws against this trait for 24 hours. 

Neifion can take a reaction whenever he is targeted by a spell or within the area of a spell's effect and the caster of the spell is within distance of Neifion's walking speed.

Swipe: Neifion moves up to his speed and makes a bite attack. On a hit and if the target fails the saving throw, add the following effects. If it requires a spell attack roll, the creature has disadvantage on the spell attack. If the spell requires concentration, the spell fails and the caster takes necrotic damage equal to the level of the spell. If Neifion takes damage from an opportunity attack while moving, the target automatically succeeds on the saving throw and Neifion automatically loses concentration on one spell he was concentrationg on. 

Neifion has 3 legendary actions, choosing from the options below. He can only use one option at a time and only at the end of another creature's turn.

Fang of fear: Cost, 1 action: Neifion makes a bite attack. 

Claw in the dark: Cost, 1 action: Neifion makes a claw attack.

Shadow magic: Cost, 2 actions: Neifion casts a spell.

Archfey ability: Cost, 2 actions: Neifion regains the use of his archfey presence. 

Shadow walk: Cost, 1 action: Neifion moves up to his speed.