Armor Class 18 (natural armor)
Hit Points 187 (25d8 + 75)
Speed 30 ft., fly 40 ft.
Saving Throws INT +8, CHA +9
Skills Deception +9, Insight +6, Perception +6, Persuasion +9
Damage Resistances cold, [object Object]
Damage Immunities fire, poison
Condition Immunities poisoned
Senses darkvision 120 ft., passive Perception 16
Languages Draconic, Infernal, telepathy 120 ft.
Challenge 15
Devil's Sight. Magical darkness doesn't impede the abishai's darkvision.
Magic Resistance. The abishai has advantage on saving throws against spells and other magical effects.
Magic Weapons. The abishai's weapon attacks are magical.
Multiattack. The abishai makes two attacks, one with its claws and one with its longsword, or it casts one spell from its Innate Spellcasting trait and makes one claw attack.
Longsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 5 (1d8 + 1) slashing damage, or 6 (1d10 + 1) slashing damage if used with two hands.
Claws. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 12 (2d8 + 3) piercing damage. If the target is a creature, it must succeed on a DC 16 Constitution saving throw or take 11 (2d10) poison damage and become poisoned for 1 minute. The poisoned target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Mordenkainen's Tome of Foes, p. 162