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Swarm of Crystalline Ice Mephits

Local tribes call them the Whispering Teeth. They are believed to be the frozen breath of a dying winter god, caught in the moment of expiration and turned into predatory crystal.

Monsters
Large elemental · CR 5 · Uncommon

Swarm of Crystalline Ice Mephits

A collective of jagged, semi-transparent ice spirits masquerading as natural tundra formations while scavenging the remains of giant kills.
AC14
HP90/90
CR5
Init
STR
DEX
CON
INT
WIS
CHA
ConditionsNone

Combat

AC 14 · HP 90 · CR 5

Swarm of Crystalline Ice Mephits

Large elemental (swarm of tiny elementals), neutral evil
Armor Class14 (Natural Armor)
Hit Points90 (12d10 + 24)
Speed
30 ft.,
fly 30 ft.
STR
DEX
CON
INT
WIS
CHA
Saving ThrowsDexterity
SkillsPerceptionStealth
Damage Resistances
Piercing and Slashing from nonmagical attacks,
Poison
Immunities
Cold
Weaknesses
Bludgeoning,
Fire
Senses
Darkvision 60 ft.,
Passive Perception 13
Languages
Aquan,
Auran,
Tinkling Melodic Chimes
Challenge5
False Appearance. While the swarm remains motionless hanging from a surface, it is indistinguishable from ordinary icicles.
Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny mephit. The swarm can't regain hit points or gain temporary hit points.
Death Burst. When the swarm dies, it explodes in a burst of jagged ice. Each creature within 5 feet of it must make a Dexterity saving throw, taking 7 () cold damage and 7 () piercing damage on a failed save, or half as much damage on a successful one.

Actions

Multiattack. The swarm makes two Crystal Slash attacks.
Crystal Slash. Melee Weapon Attack: to hit, reach 0 ft., one creature in the swarm's space. Hit: 14 () slashing damage plus 7 () cold damage, or 7 () slashing damage plus 3 () cold damage if the swarm has half of its hit points or fewer.
Frost Breath (Recharge 6). The swarm exhales a 15-foot cone of freezing air and crystal dust. Each creature in that area must make a Constitution saving throw, taking 21 () cold damage on a failed save, or half as much damage on a successful one.

Reactions

Fractal Refraction. When a creature the swarm can see within 30 feet targets it with a ranged attack, the swarm shifts its crystalline bodies. The attacker must make a Wisdom saving throw or have disadvantage on the attack roll as the light splits into confusing patterns.
Role
Environmental Ambush Striker
Built for
5

Feats

Alert

Augmentations

Crystalline Shell

Notes for the game master

Remember that swarm damage is halved when the swarm is at half health or lower.
The swarm is particularly vulnerable to hammers and fire-based magic.

Tactics

  1. Opening

    Drops from the ribs of a behemoth using its False Appearance, attempting to start its turn inside a player's space for a surprise Crystal Slash.

  2. Mid-fight

    Focuses on the creature with the lowest Armor Class, utilizing Frost Breath whenever it recharges to hit multiple targets.

  3. End of the fight

    It stays in the thick of the party, ensuring that when it dies, its Death Burst hits as many enemies as possible.

  4. Retreat

    The swarm flees if reduced to 10 hit points, scattering into individual tiny crystals that are difficult to track in a blizzard.

How it fights

Stays within the target's space to prevent easy movement without provoking opportunity attacks.
Targeting magic users who lack physical defenses against slashing damage.
Utilizing high altitudes to drop on targets, taking advantage of gravity for impact.

Who it attacks first

Weakened or bloodied targets
Unarmored spellcasters
Small creatures

Works well with

Winter Wolves (Wait for wolves to use cold breath, then the swarm moves in)
Remorhaz (Scavenging the scraps of its hot kills)
Ice Storm (Flourish in the chaotic cold weather)

How to beat it

Fireball (Targets weakness and hits whole swarm)
Thunderwave (Disruption of crystalline structure)
Bludgeoning weapons (Warhammers)

Ways to avoid a fight

They can be bribed with highly reflective jewels or gemstones.
They can be tricked into reflecting a specific beam of light to solve a puzzle.
Characters who speak their melodic chime language can negotiate safe passage through their territory.

Ecology

The swarm appears as a glittering cloud of jagged, glass-like shards. Each individual mephit is semi-transparent, reflecting the pale tundra sun in brilliant fractals. When they move, they resemble a localized blizzard of broken crystal.

Behavior

They cling to high vantage points like the frozen ribs of long-dead behemoths, remaining perfectly still to look like massive icicles. They are patient scavengers, watching for Winter Wolves to strike and then dropping onto the weakened survivors to finish the job.

How it lives

They feed on the residual elemental heat and lingering life force of dying creatures, speeding up the freezing process of the environment through their presence.

Lair

The ribcages and hollowed skulls of titan-class creatures where frozen winds create natural resonant frequencies.

Habitat
Arctic tundras, glacial peaks, and the skeletal remains of mega-fauna.

Signs that it is near

Abnormally symmetrical icicles hanging from heights
Tinkling chime-like sounds carried on the wind
Piles of frozen carcasses stripped of soft tissue
Fractured crystalline dust on the ground

Tags

Tundra,
Elemental,
Swarm,
Cold

Lore

Local tribes call them the Whispering Teeth. They are believed to be the frozen breath of a dying winter god, caught in the moment of expiration and turned into predatory crystal.

What drives it

To consume the heat of warm-blooded creatures and maintain the eternal winter of their territory.

After the fight

The area becomes littered with rapidly melting glass shards that leave behind a fine, freezing mist for 1 hour.

Variants

Volcanic Glass Swarm (Fire damage instead of Cold)
Salt Crystal Swarm (Dehydration focus)

Hooks

Plot hooks

A famous explorer was last seen entering the Ribs of the Ancient, but only his frozen gear remains.
The local village is losing its livestock to 'flying glass' that strikes during snowstorms.
An eccentric wizard wants a single Crystalline Mephit trapped in a lantern to use as a focus for light spells.

How to use it

Environmental hazard in a giant's graveyard
Scavengers appearing after a fight with Winter Wolves
Guardian of a frozen treasure hoard

Treasure

Crystalline Shards (worth 250gp as components)
Frozen gems found in the gizzards of the mephits
Elemental Water Essence

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