Hallucigenia, the Spined Crawler

Tiny Aberration, Unaligned

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Challenge: 1/4 (50 XP)
Proficiency Bonus: +2

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Armor Class 14 (natural armor)

Hit Points 9 (2d6 + 2)

Speed 20 ft., climb 10 ft.

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STR	DEX	CON	INT	WIS	CHA
3 (–4)	14 (+2)	13 (+1)	2 (–4)	12 (+1)	5 (–3)

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Saving Throws

Dex +4

Skills

Stealth +6, Perception +3

Damage Resistances

Piercing; Bludgeoning from nonmagical attacks

Condition Immunities

Charmed, Frightened

Senses

Darkvision 30 ft., Tremorsense 10 ft., Passive Perception 13

Languages —

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Traits

Spined Deflection

Any creature that hits Hallucigenia with a melee attack while within 5 feet takes 2 (1d4) piercing damage from its defensive spines.

Alien Anatomy

Hallucigenia’s physiology defies logic. It has advantage on saving throws against being grappled or restrained.

Wall Crawler

Hallucigenia can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Camouflaged Skitterer

Hallucigenia has advantage on Dexterity (Stealth) checks made to hide on rocky or sediment-covered surfaces.

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Actions

Proboscis Jab

Attack (Melee Weapon): +4 to hit, reach 5 ft., one creature.
Hit: 3 (1d4 + 1) piercing damage.

If the target is surprised, it must succeed on a DC 11 Constitution saving throw or be disoriented until the end of its next turn, having disadvantage on its next attack roll or ability check.

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Reactions

Recoil Curl (1/Short Rest)

When a creature misses Hallucigenia with a melee attack, it may immediately move up to 10 feet without provoking opportunity attacks. It gains resistance to all damage until the start of its next turn.

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Tactics

Hallucigenia prefers stealth and survival over confrontation. It clings to walls or ceilings and remains motionless, waiting for the right moment to jab or escape. If attacked, it recoils and attempts to flee. In groups, they can swarm and disorient lone creatures, creating an opening for larger predators or hazards. Hallucigenia is especially dangerous in dark, claustrophobic, or underwater environments where its alien shape and movement can cause confusion or fear.

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DM Notes

• Use Hallucigenia as a trap-like creature in primeval ruins, time-lost vaults, or deep-sea ecosystems.
• Great for low-level encounters involving unnatural or alien biology.
• Especially effective when paired with more aggressive predators (e.g., Anomalocaris).
• Can be the target of an Identify spell or lore check to reveal its prehistoric origins.

Swarm of Hallucigenia

Medium Swarm of Tiny Aberrations, Unaligned

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Challenge: 2 (450 XP)
Proficiency Bonus: +2

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Armor Class 15 (natural armor)

Hit Points 45 (6d8 + 18)

Speed 20 ft., climb 20 ft.

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STR	DEX	CON	INT	WIS	CHA
6 (–2)	15 (+2)	16 (+3)	1 (–5)	12 (+1)	3 (–4)

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Saving Throws

Dex +4

Skills

Stealth +6, Perception +3

Damage Resistances

Bludgeoning, Piercing, Slashing (nonmagical)

Condition Immunities

Charmed, Frightened, Grappled, Paralyzed, Petrified, Prone, Restrained, Stunned

Senses

Darkvision 30 ft., Tremorsense 10 ft., Passive Perception 13

Languages —

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Traits

Swarm

The swarm can occupy another creature’s space and vice versa, and it can move through any opening large enough for a Tiny creature. The swarm can’t regain hit points or gain temporary hit points.

Spined Mass

Any creature that hits the swarm with a melee attack while within 5 feet takes 4 (1d8) piercing damage from dozens of sharp spines.

Skittering Nightmare

When a creature sees the swarm appear within 10 feet for the first time, it must succeed on a DC 12 Wisdom saving throw or be startled, granting the swarm advantage on attack rolls against that creature until the end of its next turn.

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Actions

Needle Claws (Swarm Bite)

Attack (Melee Weapon): +4 to hit, reach 0 ft., one creature in the swarm’s space.
Hit: 13 (3d8) piercing damage, or 6 (1d8 + 2) piercing damage if the swarm has half its hit points or fewer.

If the target is wearing armor, it must succeed on a DC 12 Dexterity saving throw or have its armor briefly tangled in the swarm, giving the swarm advantage on its next attack against that target.

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Reactions

Curl & Scatter (1/Short Rest)

When the swarm takes damage from a melee weapon attack, it curls inward, then scatters outward in a bladed wave. Until the start of its next turn:

• The swarm gains resistance to all damage.
• Creatures that move through or remain in its space take 3 (1d6) piercing damage.

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Tactics

The Swarm of Hallucigenia overwhelms its prey through confusion and relentless, razor-like contact. It drops from walls or ceilings to envelop a creature, using its Spined Mass and Skittering Nightmare to disrupt and disorient. It avoids radiant light and fire but excels in claustrophobic ruins, fungal caverns, or void-touched chambers.

The hallucigenia is a strange and very small worm creature that you wouldn’t like to crunch under your feet…

Originally Posted by LordArchaon of the Wizards Community forums.

On this Thread

Hallucigenia is an aquatic organism considered akin to velvet worms. Like some of those, it has a very flexible body and can actually use the spines on its back by bending all or part of its body.

It is said that the strong poison, which can be lethal for non aquatic creatures who get poisoned underwater, comes from some kind of microscopic spores that come from the exotic rifts in which the hallucigenia lives.

Hallucigenia is found in the Middle Cambrian, wormlike it had none of the features generally associated with heads: mouth, eyes, or other sensory organs.

Hallucigenia CR 1/2

Always N Fine vermin

Init +2; Senses Darkvision 60ft.; Listen +0, Spot +4;

Languages none

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AC 21, touch 20, flat-footed 19;

(+8 size, +2 Dexterity, +1 natural)

hp 2 (1/2 HD)

Fort +2, Ref +2, Will +0

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Speed 5 ft. (1 square), Climb 5ft..

Melee spikes +10 (poison)

Space 1/2 ft.; Reach 0 ft.

Base Atk +0; Grp -13

Atk Options poison

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Abilities Strength 3, Dexterity 14, Constitution 10, Intelligence -, Wisdom 10, Charisma 2

Feats Weapon Finesse (B)

Skills Hide +10, Listen +4, Move Silently +6, Spot +0, Climb +6

Advancement –

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Poison (Ex) Injury, Fortitude DC 15, initial damage Paralysis for 1d10 rounds, secondary damage Paralysis for 1d10 minutes. The poison does not derive from the body of the hallucigenia, but from other micro-organisms that live in symbiosis with the vermin‘s spikes, so the posion is very strong for such a small animal.

Skills

A hallucigenia has a +4 racial bonus on Move Silently, Climb and Spot checks. Additionally, it uses its Dexterity modifier for the Climb skill.

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Strategies and Tactics

Although being very colored and not capable of mimetic behavior, the hallucigenia can be mistaken for something else or simply not be seen among all the other colored plants of the rift by creatures not familiar with the environment and this can result in injury and poisoning.

Ecology

Hallucigenia is a pacific detritivorous animal that lives in symbiosis with the corals, sponges, and algae of the rift. Being poisonous, it prevents many animals to eat the barrier-forming organisms, making them able to grow peacefully.

Environment: The hallucigenia needs a tropical rift environment and specific combinations of algae, sponges and corals, that the small worm “cleans”, by eating dead parts or other detritus that periodically gets to fill the orifices of corals and sponges.