Rat Swarm - Dungeons on Automatic Bestiary

Animal · SM +0 Rat Swarm [Monster Manual, page 239]

Attributes

ST4

DX12

IQ3

HT14

HP6

Will9

Per12

FP12

Basic Speed6

Basic Move4

Dodge10

DR0

Melee attacks

Usage	Level	Damage	Reach
Swarm BiteNo attack roll and no active defense. The swarm steps into close combat; the target automatically takes 1d cutting as large-area injury, reduced by DR normally. Retreating or dodging and dropping at least one yard away is the only way to avoid it.	no roll	1d cutting	C

Traits (10)

Combat Reflexes
Flexibility
Fur
Night Vision 4
Reduced Consumption 3 (Cast Iron Stomach)
Resistant to Metabolic Hazards +8
Semi-Upright
Short Lifespan 4
Silence 2
Wild Animal

Skills (4)

14Climbing
14Escape
13Scrounging
14Stealth

Notes

GCS ancestry draft: gcs/rat-swarm.gct
Source template total: 46 points.
Library-rebuilt template total: 46 points.
CER was computed from parsed Typical Stats using the Dungeons On Automatic baseline CER path.
Review attacks, special abilities, encounter frequency, treasure, grappling, and GCS modifiers before approval.
Swarm: the swarm is dispersed at 0 HP and destroyed at -HP. It cannot be slammed or grappled, is immune to crippling injuries, and takes reduced damage from most physical blows (Diffuse).

Encounter rating

CER24

Offense20

Protection4

Threat tierminor

Appearing1

Wandering4

GCS v5 downloads

Where this one came from

Source record: Rat Swarm [Monster Manual, page 239]
Source system: gurps_4e_fan_conversion / author_permission
Released under: cc_by_4_0
Conversion: 0.2.0-reviewed
Review status: approved
Credit: Original GURPS conversion by Enraged Eggplant, from Monsters (May 11, 2024); adapted and republished with permission.

GCS ancestry draft: gcs/rat-swarm.gct
Source template total: 46 points.
Library-rebuilt template total: 46 points.
CER was computed from parsed Typical Stats using the Dungeons On Automatic baseline CER path.
Issue #5: the automatic swarm bite was added from the source's Cosmic (no die roll required, no active defense allowed) construction.
CER recomputed from the reviewed Typical Stats through the canonical Dungeons on Automatic CER path: OR 20, PR 4, CER 24, threat tier minor.
Conversion baseline reported OR 0, PR 4, CER 4 (tier minor). The reviewed values come from the consumer CER implementation, which rounds damage once after the damage-type multiplier and credits ranged accuracy; the conversion baseline ceilinged the damage base first and ignored range.
Encounter metadata derived (solitary): average number appearing 1, wandering weight 4. Encounter metadata derived for 0.2.0 from the reviewed threat tier and creature class (appearing: minor 4 / standard 2 / major 1 / severe 1, forced to 1 for solitary classes — including swarms, which are a single multi-body creature — and raised to 6 for gregarious minor creatures; wandering weight: minor 4 / standard 3 / major 2 / severe 1). The fan-conversion source states no appearing-in-numbers or wandering values, so these are derived, not source mechanics.
Lair, treasure, and grappling remain unpopulated in 0.2.0 by package policy: the authorized fan-conversion source states no lair, treasure, or grappling values, and review declines to invent them. See review/policy/0.2.0-empty-field-policy.md.
Review approved by automated-mechanical-review on 2026-07-26 (batch ee-2026-07-26-b4-special-mechanics); GCS fidelity check passed, DOA playability check passed.
Special-mechanics record. Mechanics the CER path cannot price are named per record in review/reports/cer-audit.md rather than folded into the number, and encounter counts are capped where a save-or-disable attack is present.

Enraged Eggplant GURPS monster conversions; used, adapted, and republished with unrestricted permission from the author. Portrait and tokens are AI-generated original art. Sources and credits.