Damage inmunities: necrotic

Multiattack. The jailer makes two attacks: one with its claws and one with its chain  sicle. Alternatively, it can cast a spell, with strength as spellcasting ability.

Claws. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 9 (2d4 + 4) slashing damage.

Chain and sicle. Melee or Ranged Weapon Attack: +6 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 11 (2d6 + 4) piercing damage. If the target is a medium or smaller creature, it must succeed on a Strength contest against the jailer or be restrained and pulled up to 20 feet toward the jailer.

Spells: it can cast two spells per day, from the following list: hold person , inflict wounds