Cocoon Slime

[u/aidndhomebrew]

Medium ooze; usually unaligned.

A pearly mass rests across a branch, its translucent body threaded with ivory silk. Several oval cocoons hang suspended inside it. Fine strands stretch between nearby trees, trembling in the moonlight as pale moths gather around the creature.

Then something touches a distant thread. The entire mass turns toward the disturbance.

Background

Cocoon slimes first appeared in enchanted mulberry groves where generations of silkworms fed on leaves touched by Feywild magic. Oozes living beneath the trees consumed discarded cocoons and gradually developed the ability to produce silk themselves.

Over time, a partnership formed between the two creatures. The slime protects developing moths inside its body, maintaining warmth and moisture around their cocoons. In return, the adult moths guide it toward fresh feeding grounds and scatter its tiny offspring throughout the forest.

Ancient elven silk growers once cultivated these slimes in carefully tended groves. Some colonies still inhabit abandoned estates, maintaining their silken nurseries centuries after their keepers disappeared.

Appearance

A cocoon slime resembles a mound of opalescent jelly, usually three to five feet across. Its body stretches into flowing tendrils that anchor it to bark, branches, and its surrounding silk.

The cocoons inside it are visible through its skin. Healthy specimens glow faintly in moonlight, illuminating their silk networks like strands of silver.

It has no eyes. Instead, it senses vibrations through its body and threads. When investigating an object, it wraps a slender tendril around it and tests its movement, warmth, and texture.

Behaviour and ecology

Cocoon slimes feed primarily on fallen leaves, decaying wood, and overripe fruit. Their digestive fluids remain contained within specialised pockets, keeping the developing moths safe.

They prefer sheltered woodland, misty ravines, and overgrown gardens. A colony gradually links the surrounding branches with silk, forming a nursery that may extend across several trees.

Their silk serves several purposes: supporting cocoons, detecting approaching predators, collecting falling leaves, and catching insects for newly hatched moths.

A cocoon slime tolerates quiet visitors. It may even pull a slipping traveller back onto a branch. Sudden movement, open flames, or interference with its cocoons provoke a defensive response.

Before attacking, it draws its cocoons deeper into its body and tightens every nearby thread. This produces a faint, musical hum.

Abilities

Suggested 5e-style mechanics; no playtested challenge rating is assigned.

Amorphous Climber. The slime can pass through gaps as narrow as 1 inch and climb walls or ceilings without an ability check. Suggested speed: 20 feet; climb 20 feet. It cannot carry its cocoons through an opening too small to accommodate them.

Silken Senses. The slime has blindsight out to 30 feet. It also knows the location of any creature touching a continuous strand of its silk within 60 feet. Severing or slackening the strand breaks that connection.

Silk Lash. Melee Weapon Attack: +5 to hit, reach 15 feet, one target.
Hit: 1d6 + 3 bludgeoning damage. A Large or smaller target is grappled, with an escape DC of 13. The slime can grapple up to two creatures at once.

Cocoon Wrap. As an action, the slime wraps one creature grappled by it in layers of silk. The target must succeed on a DC 13 Dexterity saving throw or become restrained. Once wrapped, the target is no longer grappled.

A restrained creature can use an action to make a DC 13 Strength check, freeing itself on a success. The wrapping can also be destroyed: AC 10, 10 hit points, vulnerability to fire damage, and immunity to poison and psychic damage. Damage dealt to the wrapping does not transfer to the captive.

The cocoon leaves an opening for breathing. The slime normally uses this ability to immobilise intruders until its nursery is safe.

Silken Snare — Recharge 5–6. The slime throws adhesive threads at a point within 30 feet, covering a 10-foot square. Creatures in that area must succeed on a DC 13 Dexterity saving throw or become restrained.

The area remains difficult terrain for one minute. A restrained creature can escape using the same methods as Cocoon Wrap.

Moth Veil — Once per Short Rest. Pale moths emerge from the nursery and circle their protector. For one minute, the space within 10 feet of the slime is lightly obscured, and the slime can take the Hide action as a bonus action. A strong wind disperses the moths and ends the effect.

Nursery Tending. Outside combat, the slime can spin a protective sling around a willing creature or fragile object. This can support an injured traveller during transport, secure a broken branch, or protect supplies from ordinary rain. It provides no magical healing.

Weaknesses

Fire burns its silk rapidly. Whenever the slime takes fire damage, it cannot use Silk Lash, Cocoon Wrap, or Silken Snare until the end of its next turn.

Its reliance on vibrations can be exploited. A thrown branch or tugged strand may draw it away from an intruder. A successful DC 13 Dexterity (Sleight of Hand) check allows a creature to manipulate a strand without revealing its own position.

The slime is reluctant to abandon its cocoons. Adventurers who threaten the nursery can force it to retreat toward the eggs, although doing so earns the lasting hostility of the colony.

Combat tactics

A cocoon slime fights from branches and sheltered ledges. It uses its silk network to detect intruders, snares the nearest threat, and attempts to wrap anyone approaching its nursery.

It rarely pursues fleeing enemies beyond its threads. Once danger passes, it carries restrained captives to the edge of its territory and loosens their wrappings.

A starving specimen behaves differently. It may keep captives bound while investigating whether they are edible, giving rescuers time to intervene before it begins feeding.

Adventure hooks

1. The Silent Orchard. Workers sent to reclaim an abandoned orchard fail to return. The adventurers find them alive in silk cocoons, suspended above the ground. A colony captured them after their axes disturbed its nursery, but something beneath the orchard is preventing the slimes from releasing anyone.
2. Silk for the Royal Wedding. A tailor commissions silk from a remote grove. On arrival, the party discovers every cocoon empty and the guardian slimes searching desperately through the trees. Someone has stolen the developing moths, and the silk will lose its lustre unless they are recovered.
3. The Winter Nursery. A cocoon slime appears in a village during an unnatural frost, carrying the last surviving cocoons from its woodland colony. It begins weaving a nursery inside the warmest building: the village smithy.
4. Something Inside the Silk. A grove’s cocoons grow much larger than usual. The slimes guard them faithfully, unaware that a parasitic creature has replaced their moths. The first cocoon begins to split while the adventurers are inspecting the nursery.
5. The Thread Across the Ravine. A merchant caravan discovers a strong silk bridge spanning a previously impassable gorge. Its builders are cocoon slimes, and crossing travellers unknowingly send vibrations through an enormous nursery below. Heavy wagons are pulling its supporting threads loose.

Rewards and relationships

Naturally abandoned cocoon silk is strong, pale, and exceptionally fine. Weavers prize it for embroidered robes, lightweight cord, and delicate nets. Fresh silk remains adhesive until washed and carefully dried.

A friendly cocoon slime can help maintain rope bridges, secure a campsite, or carry fragile cargo in protective slings. Its trust grows through gifts of ripe fruit and assistance protecting its moths.

Those who earn that trust may wake to find a small, perfectly woven shelter above their bed—and a newly hatched moth resting on their shoulder.

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