The Jailer (5e Creature)
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Large undead, chaotic evil
Damage Immunities poison
Magic Resistance. The jailer has advantage on saving throws against spells and other magical effects.
Undead Fortitude. If damage reduces the jailer to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the jailer drops to 1 hit point instead.
Multiattack. The jailer makes two melee attacks.
Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage.
Chain. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 18 (4d6 + 4) slashing damage. The target is grappled (escape DC 14) if the jailer isn't already grappling a creature. Until this grapple ends, the target is restrained and takes 7 (2d6) piercing damage at the start of each of its turns.
Imprison. The jailer makes one chain attack against a Medium or smaller target it is grappling. If the attack hits, the target is also imprisoned in the jailer cage, and the grapple ends. While imprisoned, the target is restrained, it has half cover against attacks and other effects outside the jailer, and it takes 9 (3d6) acid damage at the start of each of the jailer turn's. The jailer can have only one creature imprisoned at a time.
If the jailer takes 15 damage or more on a single turn from the imprisoned creature, the jailer must succeed on a DC 12 Constitution saving throw at the end of that turn or release the creature, which falls prone in a space within 10 feet of the jailer. If the jailer dies, a imprisoned creature is no longer restrained by it and can escape from the corpse by using 15 feet of movement, exiting prone.
The Jailer's hulking torso is formed from the remains of countless cadavers. Hanging from this shroud of decayed flesh are cages where the souls of those killed by the Jailer remain trapped. These souls can be summoned as rotting corpses to serve the Jailer's command. As the undead mob harries his prey, their master crushes the victim beneath his cage. The legends hint that some darker secret lies hidden within the Jailer's hideous frame.