Grimmlet Swarm

Flowing over the landscape like a glass carpet, this mass of smoky crystalline shards moves in a manner most unnatural. Occasionally, a bolt of black or purple energy arcs between two or more of the shards in the swarm.

Grimmlet Swarm

Large swarm of Tiny monstrosities, unaligned
Armor Class 15 (natural armor)
Hit Points 199 (21d10 + 84)
Speed 0 ft., fly 30 ft. (hover)
STR DEX CON INT WIS CHA
17 (+3) 12 (+1) 19 (+4) 3 (−4) 10 (+0) 18 (+4)

Damage Immunities psychic
Damage Resistances bludgeoning, piercing, and slashing from nonmagical weapons.
Condition Immunities blinded, charmed, deafened, petrified, poisoned, stunned, unconscious
Senses blindsense 120 ft., passive Perception 10
Languages
Challenge 10 (5,900 XP)

Innate Spellcasting. The grimmlet swarm’s innate spellcasting ability is Charisma (spell save DC 16, +8 to hit with spell attacks). It can innately cast the following spells, requiring no material components:
At will: crushing curse (as 11th-level cantrip), maddening whispers, minor illusion
3/day each: hypnotic pattern, major image, void strike
1/day each: hallucinatory terrain

Reproduce. If the grimmlet swarm is dealt damage by a spell that does not reduce it to 0 hit points, a number of new grimmlets equal to the level of the spell slot used to cast the spell are created in the nearest empty spaces to the injured grimmlet swarm. If the grimmlet swarm is injured by a spell cast using innate spellcasting, the number of new grimmlets created is equal to the level of the spell cast. Grimmlet swarms injured by cantrips or at-will innate spells create one new grimmlet. New grimmlets created by the grimmlet swarm are not subsumed into the swarm. They instead form a new swarm once sixteen or more new grimmlets have been created.

Maze of Edges. A creature that attempts to move out of or through the grimmlet swarm must make a DC 15 Dexterity saving throw or take 19 (3d10 + 3) slashing damage.

Shroud of Whispers. As a bonus action, the grimmlet swarm can cast crushing curse or maddening whispers on all creatures that share its space.

Swarm. The grimmlet swarm can occupy another creature’s space and vice versa, and the swarm can move through any opening large enough for a single grimmlet. The swarm can’t regain hit points or gain temporary hit points.

Actions

Multiattack. The grimmlet swarm makes three attacks with its crystal edges.

Crystal Edges. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 19 (3d10 + 3) slashing damage and 20 (3d10 + 4) psychic damage.

Reactions

Enervating Maelstrom. When the grimmlet swarm is reduced to 0 hit points, it explodes in a plume of ennui that deals 42 (12d6) psychic damage and 1d3 levels of exhaustion to all creatures within 20 feet of it. Creatures that make a DC 16 Dexterity saving throw take only half of the psychic damage and one level of exhaustion.

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