Geumhyeoreo 금혈어

Huge swarm of tiny monstrosities, chaotic neutral

Armor Class 16 (natural armor)

Hit Points 135 (18d12 + 18)

Speed 0 ft., swim 60 ft.

STR 8 (−1) · DEX 18 (+4) · CON 12 (+1) · INT 6 (−2) · WIS 14 (+2) · CHA 8 (−1)

Saving Throws Dex +7

Skills Perception +5, Stealth +7

Damage Vulnerabilities fire

Damage Resistances bludgeoning, piercing, slashing

Damage Immunities poison

Condition Immunities charmed, frightened, grappled, paralyzed, petrified, prone, restrained, stunned

Senses darkvision 60 ft., passive Perception 15

Languages — (the swarm has a limited collective consciousness)

Challenge 9 (5,000 XP)

Traits

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 fish. The swarm can’t regain hit points or gain temporary hit points.

Coordinated Assault. The swarm has advantage on attack rolls against a creature if at least one other Geumhyeoreo Swarm is within 5 feet of the creature.

Lacerating Scales. A creature that touches the swarm or hits it with a melee attack while within 5 feet of it takes 5 (2d4) slashing damage.

Noise Sensitivity. If the swarm takes thunder damage, or if three or more creatures within 30 feet spend their actions making sustained, loud noise (drums, clanging metal, thunderwave, etc.), the swarm is stunned until the end of its next turn.

Invasive Hunters. The swarm can enter a hostile creature’s space and stay there. The first time in a turn that the swarm enters a creature’s space, that creature must succeed on a DC 15 Constitution saving throw or be Infested (see the Infestation action).

Actions

Multiattack. The swarm makes two Slashing Rush attacks, or one Slashing Rush attack and one Infestation attack if a creature is in its space.

Slashing Rush. Melee Weapon Attack: +7 to hit, reach 0 ft., one target in the swarm’s space. Hit: 27 (6d8) slashing damage, or 13 (3d8) slashing damage if the swarm has half of its hit points or fewer.

Infestation. One creature in the swarm’s space must make a DC 15 Constitution saving throw. On a failure, razor-finned fish burrow into the creature’s body, and the target is Infested. An Infested creature takes 9 (2d8) slashing damage at the start of each of its turns as the fish carve its insides. At the end of each of its turns, the creature can repeat the saving throw, ending the effect on a success. The effect also ends if the creature is submerged in boiling water or takes fire damage.

Bonus Actions

Reform (Requires at least 30 hit points). If the swarm is stunned or restrained, it can shatter apart and re-coalesce elsewhere in the same body of water. The swarm teleports up to 60 feet to an unoccupied space it can see that contains water, becoming no longer stunned or restrained when it arrives.

Reactions

Blade Burst. When the swarm takes damage from a creature within 5 feet, it lashes out. Each creature within 5 feet of the swarm must succeed on a DC 15 Dexterity saving throw or take 7 (2d6) slashing damage.

Lore

Schooling fish (around a hundred together) with razor-sharp teeth and a ravenous appetite.

The name Geumhyeoreo (금혈어) is made up of three characters: 금 “gold,” 혈 “blood,” and 어 “fish.” The literal meaning—“Golden Blood Fish”—immediately highlights an inner contradiction that is key to understanding this monster’s nature. In Korean culture, the character for gold (금) is traditionally linked to divinity, imperial power, holiness, and high status. Gold appears in descriptions of sacred beings such as the Four Divine Creatures (Sayeongsu), including the dragon, the kirin, and the phoenix. Creation myths and hero legends often feature golden eggs, golden objects, or golden animals, underscoring their supernatural or noble origins. By contrast, the character for blood (혈) in folklore and myth carries an entirely different weight, connected to violence, rage, death, curses, and vengeful spirits. Thus the “bloody” aspect of Geumhyeoreo’s name clashes sharply with its “golden” half. The golden side may stand for an originally noble or even divine potential that was twisted or cursed, turning into something bloody and deadly. Geumhyeoreo might have been created as a sacred fish but somehow lost its divine destiny, becoming an aggressive, voracious creature that hunts in swarms to satisfy its endless wrath.

According to the only known source, the Cheonseon Japgi, Geumhyeoreo is “two to three chi” long. A chi varied through history but averages about two to four inches (6–9 cm), making it unusually small for a monster. This modest size is deceptive. Its main anatomical feature is scales and fins sharp as blades, which serve as its primary weapons. They inflict slicing wounds and can even penetrate a victim’s flesh like parasites. The creature’s golden coloring may lure prey or be a remnant of its former noble state. Its “bloody” nature might show in the color of its fins, its eyes, or patterns on the body resembling fresh or dried clots of blood.

From Korean Bestiary 5E, p. 40 · Fern Flower Press