Erinyes

Medium fiend (devil), lawful evil

Armor Class 18 (plate)
Hit Points 153 (18d8 + 72)
Speed 30 ft., fly 60 ft.

Saving Throws Dex +7, Con +8, Wis +6, Cha +8
Damage Resistances cold; bludgeoning, piercing, and slashing from nonmagical attacks that aren't silvered
Damage Immunities fire, poison
Condition Immunities poisoned
Senses truesight 120 ft., passive Perception 12
Languages Infernal, telepathy 120 ft.
Challenge 12 (8,400 XP)

Hellish Weapons. The erinyes's weapon attacks are magical and deal an extra 13 (3d8) poison damage on a hit (included in the attacks).
Magic Resistance. The erinyes has advantage on saving throws against spells and other magical effects.

Actions

Multiattack. The erinyes makes three attacks.
Longsword. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) slashing damage, or 9 (1d10 + 4) slashing damage if used with two hands, plus 13 (3d8) poison damage.
Longbow. Ranged Weapon Attack: +7 to hit, range 150/600 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 13 (3d8) poison damage, and the target must succeed on a DC 14 Constitution saving throw or be poisoned. The poison lasts until it is removed by the lesser restoration spell or similar magic.

Reactions

Parry. The erinyes adds 4 to its AC against one melee attack that would hit it. To do so, the erinyes must see the attacker and be wielding a melee weapon.