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Rust-Mite Swarm - AI-generated fantasy Monster

Rust-Mite Swarm

Legend speaks of a chronomancer whose workshop was swallowed by a forest. His tiny automated cleaners, left without a master, evolved to feed on the passage of time itself, accelerating the age of everything they touch to scavenge the remains.

Monsters
Medium construct · CR 4 · Rare

Rust-Mite Swarm

A dense cloud of mechanical beetles that vibrate at a temporal frequency, causing metal to oxidize and crumble in seconds.
AC14
HP52/52
CR4
Init
STR
DEX
CON
INT
WIS
CHA
ConditionsNone

Combat

AC 14 · HP 52 · CR 4

Rust-Mite Swarm

Medium construct (swarm), unaligned
Armor Class14 (Natural Armor)
Hit Points52 (8d8 + 16)
Speed
30 ft fly (hover),
30 ft walk
STR
DEX
CON
INT
WIS
CHA
Saving ThrowsDexterity
SkillsPerceptionStealth
Damage Resistances
Bludgeoning, Piercing, and Slashing from nonmagical attacks
Immunities
Poison,
Psychic,
Charmed,
Frightened,
Paralyzed,
Petrified,
Stunned
Weaknesses
Vulnerable to Thunder damage
Senses
Blindsight 60 ft (Metal Detection Only),
Passive Perception 12
Languages
None
Challenge4
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 insect. The swarm can't regain hit points or gain temporary hit points.
Temporal Resonance. Any creature starting its turn in the swarm's space must succeed on a Wisdom saving throw or be under the effects of the Slow spell until the start of its next turn.
Metal Sense. The swarm can pinpoint the location of any metallic object within 60 feet.

Actions

Entropic Bites. Melee Weapon Attack: to hit, reach 0 ft, one target in the swarm's space. Hit: 14 () piercing damage, or 7 () piercing damage if the swarm has half of its hit points or fewer. If the target is wearing armor or carrying a shield made of metal, the item takes a permanent and cumulative -1 penalty to the AC it offers. Armor reduced to an AC of 10 or a shield that drops to a bonus is destroyed. If the target is carrying a metal weapon, it takes a permanent -1 penalty to damage rolls. A weapon reduced to a -5 penalty is destroyed.
Accelerated Decay (Recharge 5-6). The swarm vibrates violently. Each metallic object within the swarm's space ages 100 years in a second. One non-magical metal object of the swarm's choice (such as a weapon or a suit of armor) is immediately destroyed. If the object is being worn or carried, the creature must succeed on a Dexterity saving throw to pull the object away, taking only the Entropic Bite penalty on a failure instead of total destruction.

Reactions

Temporal Flicker. When the swarm would take damage from a melee attack, it can use its reaction to flicker forward in time, gaining a bonus to AC against that attack.
Role
Area Denial / Equipment Destroyer
Built for
5

Notes for the game master

Remember that magical items are resistant to the decay effect. Magical items receive a DC 13 Saving Throw to avoid the penalty entirely.

Tactics

  1. Opening

    The swarm stays hidden in the rusted remains of previous victims, waiting for the clank of heavy armor to approach.

  2. Mid-fight

    It focuses on the target with the highest AC made of metal, attempting to use Accelerated Decay early to soften the target.

  3. End of the fight

    Once the primary metal sources are destroyed, the swarm shifts to the next most metallic target or hovers over the fallen to feed on the remains.

  4. Retreat

    The swarm is mindless and fights until destroyed or until no metal remains within 120 feet.

How it fights

Uses its fly speed to reach the backline if a wizard is carrying a metal staff or ornate book.
Moves into the space of heavily armored fighters to trigger the Slow effect of Temporal Resonance.
Prioritizes shields and weapons first to reduce the party's effectiveness.

Who it attacks first

Paladin or Fighter in Plate Armor
Clerics with metal shields
Artificers or anyone with mechanical tools

Works well with

Rust Monsters: Together they can strip a party of all gear in two rounds.
Time Wraiths: The mites slow the party while the Wraiths drain their age.

How to beat it

Thunderwave: Can hit the entire swarm and deals double damage.
Heat Metal: While it doesn't hurt the mites as much, it can keep them away from a specific object.
Druids/Monks: Characters that do not rely on metal gear are effectively immune to the gear-stripping mechanics.

Ways to avoid a fight

A player can throw a bag of ball bearings or caltrops to distract the swarm for 1d4 rounds.
Using 'Mending' on an item currently being eaten can stabilize it, preventing the penalty for that round.

Ecology

A swirling mass of copper and brass beetles, each no larger than a fingernail. They emit a constant, high-pitched clicking and a faint blue glow from their gears. Trails of rust-colored dust fall from them like snow.

Behavior

They ignore biological matter, focusing entirely on metallic equipment. They move with unnatural jerky speed, often appearing to teleport short distances as they flicker in and out of the current timeline.

How it lives

As constructs from a dead future, they do not eat in a traditional sense. They consume the 'potential' of refined metals, breaking them down into their most entropic states to power their own internal clockwork.

Lair

Within the Temporal Glade, where the ground is a thick carpet of oxidized iron and pulverized bronze gear.

Habitat
Temporal anomalies, cursed forest clearings, or ancient clockwork ruins.

Signs that it is near

Discarded leather straps with no buckles
Piles of fine red and orange dust
The smell of ozone and wet iron
Echoes of ticking clocks that move at different speeds

Tags

swarm,
mechanical,
temporal

Lore

Legend speaks of a chronomancer whose workshop was swallowed by a forest. His tiny automated cleaners, left without a master, evolved to feed on the passage of time itself, accelerating the age of everything they touch to scavenge the remains.

What drives it

To reduce all ordered metal into entropic dust to maintain their temporal stability.

After the fight

The players are left with degraded gear, forcing them to find a master smith or use high-level magic to restore their equipment before the next major fight.

Variants

Silver-Mite Swarm: Targets lycanthropes and specifically destroys silvered weapons.
Lead-Hollowed Mites: Immune to thunder damage but have a slower movement speed.

Hooks

Plot hooks

The local blacksmith's shipment of rare star-metal was lost near the clearing.
A famous knight's 'invincible' armor was found turned to dust, and his family wants to know how.
A time-traveler is stranded in the clearing because the mites ate the copper wiring of his device.

How to use it

A trap-like encounter in a forest clearing where the party must cross quickly.
Scavengers that appear immediately after a different combat ends, targeting the party's damaged gear.

Treasure

1d6 'Chrono-Cores' (valuable to clockworkers, 50gp each)
Fine residue of precious metals (Gold or Platinum dust) if the swarm recently fed on high-value gear.

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