Gloom | New Monster for Fifth Edition (Patreon)

A gloom is an assassin that cloaks itself in supernatural camouflage, lingering in the periphery of vision and stalking its prey from the deepest shadows. A gloom looks very much like a human from the neck down, with dull, rubbery black skin. Its head, however, is another matter. Completely devoid of hair, the gloom also has no eyes. Its distended, exaggerated mouth, drawn back in a perpetual fiendish smile, is full of jagged black teeth. Despite its apparent lack of ocular organs, a gloom seems to have no trouble seeing. A gloom typically dresses in fine clothing suitable for a funeral (stylized for the local culture), snug fitting and all black. 

Gloom

Medium monstrosity, usually lawful evil

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Armor Class 23

Hit Points 212 (25d8 + 100)

Speed 30 ft.

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Abilities Str 20 (+5), Dex 24 (+7), Con 18 (+4), Int 20 (+5), Wis 19 (+4), Cha 22 (+6)

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Saving Throws Dex +13, Int +11, Wis +10

Skills Perception +16, Sleight of Hand +19, Stealth +19

Damage Immunities psychic; bludgeoning, piercing, and slashing from nonmagical weapons

Condition Immunities blinded

Senses blindsight 60 ft., passive Perception 26

Languages understands all languages but doesn't speak

Challenge 20 (25,000 XP)

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Fatal Strike. As a bonus action, the gloom can target one creature within 30 feet of it. The gloom has advantage on its first attack roll against the target provided the gloom makes its attack before the end of its next turn and it maintains its concentration (as if concentrating on a spell).

Fear Gaze. If a creature starts its turn within 30 feet of the gloom and the creature can see the gloom's face, the gloom can force the creature to make a DC 19 Wisdom saving throw. On a failure, the creature is frightened of the gloom for 1 minute. The creature can repeat its saving throw at the end of each of its turns, ending the effect on itself with a success. A creature that succeeds on its saving throw or the effect ends for it is immune to the gloom's fear gaze for 1 hour.

Magic Resistance. The gloom has advantage on saving throws against spells and magical effects.

Quiescence. Creatures have disadvantage on Wisdom (Perception) checks that rely on hearing when used to detect the gloom. 

Shadow Essence. While the gloom is wearing no armor and wielding no shield, its AC includes its Charisma modifier. 

Sneak Attack (1/Turn). The gloom deals an extra 35 (10d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally of the gloom that isn't incapacitated and the gloom doesn't have disadvantage on the attack roll.

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Actions

Dagger. Melee or Ranged Weapon Attack: +13 to hit, reach 5 ft. or 20/60 ft. range, one target. Hit: 9 (1d4 + 7) piercing damage, plus 36 (8d8) poison damage.

Coup de Grace (Recharge 4-6). The gloom makes a melee dagger attack against a creature within 5 feet of it that it has advantage against. If the attack hits, the creature must make a DC 19 Constitution saving throw. On a failed saving throw, the creature dies instantly. On a successful saving throw, the creature is stunned until the end of the gloom's next turn. The gloom's coup de grace does not work against constructs or undead.

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Reactions

Shadow Dodge. The gloom halves the damage that it takes from an attack that hits it. Immediately afterwards, the gloom magically teleports, along with any equipment it is wearing or carrying, up to 30 feet to an unoccupied space. Both the space the gloom is leaving and its destination must be in dim light or darkness.