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Crimson Swarm - AI-generated fantasy Monster

Crimson Swarm

The sect of the Iron Pulse sought a way to monitor the vast reaches of the Undermyr without exhausting their guards. By infusing spider eggs with distilled drow blood and resonant quartz, they created the Crimson Swarms. These creatures are psychically linked to the very stone of the dungeon.

Monsters
Medium swarm · Minor · Common

Crimson Swarm

A magical alarm system composed of thousands of ruby-colored spiders that consume blood and vibrate in resonance with the dungeon's energy.
AC13
HP36/36
CRMinor
Init
STR
DEX
CON
INT
WIS
CHA
ConditionsNone

Combat

AC 13 · HP 36 · Minor

Crimson Swarm

Medium swarm (tiny beasts), unaligned
Armor Class13 (Natural Armor)
Hit Points36 (8d8)
Speed
30 ft.,
Climb 30 ft.
STR
DEX
CON
INT
WIS
CHA
Saving ThrowsDexterity
SkillsPerceptionStealth
Damage Resistances
Bludgeoning,
Piercing,
Slashing
Immunities
Charmed,
Frightened,
Grappled,
Paralyzed,
Petrified,
Prone,
Restrained,
Stunned
Weaknesses
Fire,
Radiant
Senses
Blindsight 10 ft.,
Darkvision 60 ft.,
Passive Perception 12
Languages
None
ChallengeMinor
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 spider. The swarm can't regain hit points or gain temporary hit points.
Spider Climb. The swarm can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Sanguine Scent. The swarm has advantage on Wisdom (Perception) checks to locate any creature that does not have all its hit points.
Iron Pulse Resonance. When the swarm takes damage, it emits a high-pitched vibration. The regional Iron Pulse effect intensifies within 300 feet, and all Iron Pulse sentinels in the dungeon are immediately alerted to the swarm's location.

Actions

Bites. Melee Weapon Attack: to hit, reach 0 ft., one creature in the swarm's space. Hit: 7 () piercing damage plus 7 () necrotic damage, or 3 () piercing damage plus 3 () necrotic damage if the swarm has half of its hit points or fewer.
Internal Feast. The swarm targets one creature in its space that is below its hit point maximum. The target must succeed on a Constitution saving throw or take an additional 10 () necrotic damage as spiders enter its wounds. The swarm then detaches half of the damage taken from the target's maximum HP until the target finishes a long rest.

Reactions

Skittering Panic. When a creature moves within 5 feet of the swarm, the swarm can move up to half its speed without provoking opportunity attacks.
Role
Trash Mob
Built for
Level 5

Feats

Skilled (Stealth)

Augmentations

Blood Magic Infusion

Notes for the game master

The necrotic damage represents the rapid loss of blood as the spiders feed.
The Internal Feast action makes them particularly dangerous to players who are already injured.

Tactics

  1. Opening

    The swarm waits in the ceiling or vents, dropping down only when a creature is bleeding or passes directly underneath.

  2. Mid-fight

    It focuses on the target with the lowest current HP, attempting to use Internal Feast to finish them off.

  3. End of the fight

    The swarm does not flee, as it is a mindless extension of the dungeon's security system.

  4. Retreat

    The swarm fights until destroyed. Its death trigger is the primary alarm for the Drow masters.

How it fights

Ambush from above.
Prioritize wounded targets.
Utilize Swarm trait to bypass front liners.

Who it attacks first

Wounded targets
Low-AC targets
Casters

Works well with

Iron Pulse Regional Effect
Drow Inquisitors
Bleeding Traps

How to beat it

Burning Hands
Area of Effect Spells
Paladin Auras

Ways to avoid a fight

Casting Calm Emotions makes the swarm dormant.
Offering a vial of fresh blood can distract the swarm for 1d4 rounds.

Ecology

A thick, carpet-like mass of tiny spiders. Each individual spider has a translucent, faceted abdomen that glows with a faint, rhythmic crimson light, making the swarm look like a river of flowing rubies.

Behavior

They skitter through narrow pipes and cracks, congregating in areas with high air flow. They are relatively passive until they sense blood or until the Iron Pulse in the walls triggers their aggression. When attacking, they flow over targets like a liquid, seeking open wounds.

How it lives

Artificially created via Drow blood magic, these swarms do not eat solid food. They sustain themselves on the residual mana of the Iron Pulse and the fresh blood of intruders.

Lair

The Undermyr ventilation network and cooling pipes.

Habitat
Underdark, Drow Citadels, ventilation shafts, blood-magic laboratories.

Signs that it is near

Faint humming sound in the walls
Small crystalline husks in the dust
A metallic, copper-like smell in the air vents

Tags

Spider,
Blood Magic,
Detection,
Drow-Made

Lore

The sect of the Iron Pulse sought a way to monitor the vast reaches of the Undermyr without exhausting their guards. By infusing spider eggs with distilled drow blood and resonant quartz, they created the Crimson Swarms. These creatures are psychically linked to the very stone of the dungeon.

What drives it

To protect the sanctity of the Undermyr and alert their creators to the presence of warm-blooded intruders.

After the fight

The surrounding walls continue to thrum with a red light for 1 hour after the swarm's destruction, alerting patrols.

“By infusing spider eggs with distilled drow blood and resonant quartz, they created the Crimson Swarms.”
From its lore

Variants

Shadow Swarm (Deals psychic damage)
Toxic Swarm (Deals poison damage)

Hooks

Plot hooks

The party finds a survivor covered in tiny red geometric scars.
The Drow are harvesting blood from local villages to grow new swarms.

How to use it

Use as a 'tax' monster that drains resources before a big fight.
Combine with environmental hazards like narrow crawlspaces.

Treasure

1d6 Ground Ruby Dust (worth 50gp total)
Crystal Carapace Fragments

Media

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