Gelatinous Cube Monster Card art by Jeff Reitz

Gelatinous Cube Culture, Psychology, & Lore

by Alec Wilson

“The Orc fought well–tooth and nail as they do–but in the end, he was no match for the Cube. Watching him get digested alive, I almost felt for the poor bugger. Almost.”

– Vorin Grimsbeard, Dwarven Barbarian

Culture and Psychology

Gelatinous Cubes are native to the Known World. Tales of encounters with cubes are common in the histories of virtually all known populations, and cubes have been observed in nearly all climates. The largest and fastest-moving cubes live in moist, temperate zones with ample organic material to consume, such as jungles, wetlands, and rain forests. Cubes as large as 25’ on a side have been sighted in the Ataradzt Forest, where even large and huge-sized creatures fear and avoid them. And in the hot Karmiani jungles cubes are said to be active hunters that can move across the ground as fast as a man for short distances.

Accounts from reliable witnesses detail encounters with smaller, slower-moving cubes in the dungeons of the frozen north. Until recently, it was thought that cubes could not survive in the dry desert—and on the hot surface sands this may in fact be true—but the Half-Elven Ranger Balendor Goldmoon reports that deep in the Tomb of King Akademzod he was surprised by a Gelatinous Cube:

“How long it had stood there I cannot guess. It waited in the archway that led down to the crypt of the King, filling the portal with its bulk. I nearly stepped into it. I was saved only by the odd reflection of my companion’s torch, on what should have been a patch of empty air. As I leapt back, the cube seemed to shiver awake. Then it let out a high wail and groped at me with many pseudopods. I stumbled away and we fled the antechamber. Whatever the dead King’s secrets, they remain safe for now.”

Goldmoon’s report notwithstanding, the idea that all cubes lurk belowground waiting in silence for their next meal is not representative of the species as a whole. While many cubes do inhabit caves and dungeons, many more live aboveground and hunt actively. They are difficult to see in the shadowed terrain of ravines and canyons, and hard to spot even in the dappled light of forests. They tend to avoid bright sunlight and open spaces where they are more easily avoided. They pose a serious threat at night, especially to those who have camped on the ground. Many adventuring parties have reported that cubes seem drawn to campfires, and will skulk on the edges of the firelight, waiting for an opportune moment to strike.

Gelatinous Cubes were long thought silent and solitary. But Rangers, Druids, adventurers, and inhabitants of the wildlands have reported that this is not the case. Cubes have been observed using both vibration and sonic pulses to communicate not only with each other, but with Aberrations, Fey, and with a host of natural creatures. Cubes send out impulses that can be felt in the air, water, and ground. Nearby cubes respond, sometimes rushing toward the vibration, and at other times fleeing away from it. Cubes also emit sonic blasts similar to hollow shrieks. While these can be deafening to enemies engaged in combat with a cube, they also serve to call in the cube’s allies. Brownies, Pixies, Fairies, Blink Dogs, and Pseudodragons all seem particularly responsive to the high-pitched shriek of a Gelatinous Cube.

A great variety of creatures have been observed working cooperatively with cubes—from beetles and birds, to Fey, Goblins, Kobolds, Aberrations, and Troglodytes. Many are willing to lure live prey within reach of a cube, or lead it onto a fresh corpse it can scavenge, in return for protection, food scraps, or one of the glimmering prizes cubes can choose to expel from their innards. Both Fey and Goblinoids report working for long months in exchange for an excreted pile of gleaming gold, a perfectly preserved necklace, or a magical trinket.

More recently, worrying dispatches have surfaced from mariners who claim to have sighted gargantuan Gelatinous Cubes living in the oceans. If true, these marine cubes would have access to a nearly inexhaustible food source, and could grow to terrifying sizes. This would make them a threat even to large, oceangoing vessels. They would pose a danger to nearly all sea life, and might also contain unfathomable riches–scavenged from ancient shipwrecks that litter the dark sea floor.

Special Tactics

Lay in Wait. Cubes most often conceal themselves in their environment, and wait for prey to step or fall into them. They commonly occupy doorways, or the threshold of descending stairs. When outdoors they also bury themselves, then use pseudopods to cover their surface with gravel, twigs, and leaves–forming a deadly trap. Given time, cubes can climb to the rooves of natural caverns, suspending themselves over well-trodden paths in order to drop down on unsuspecting adventures.

Active Attack. Especially in warm climates, cubes can move quickly over short distances to initiate attacks. They are drawn to loud noises, to the smell of food, and to the light of small fires.

Call Minions. Cubes use vibrations and sonic pulses to call in their minions, especially birds, beetles, Fey, and Aberrations. Most often, these allies serve to disorient the prospective prey, driving them toward the hungry cube.

Regardless of tactics, when cubes encounter live prey they attempt to paralyze or grapple it, then engulf it, and digest it alive.

Note: Cubes can make themselves formless to pass through gaps 1/10th their size. When formless they are adequate climbers on natural surfaces, but are vulnerable to damage and cannot attack.

Qualities

Relentless. Once cubes catch the scent of injured prey, or injure a creature during combat, they rarely retreat. When badly injured with magic, some cubes will try to flee, but move so slowly that their best option is usually to continue the attack.

Remorseless. Cubes do not show compassion when feeding. They devour children, the wounded, and the elderly as readily as they eat hardened warriors. They make exceptions only when presented with better opportunities, such as when a small creature can lead them onto larger, more satisfying prey.

Sonic Sensitive. Cubes are extremely sensitive to sounds and vibrations. They sense footsteps and voices from 500 feet, and appear to react to a spectrum of sound that is beyond the sense of humanoids.

Heat Avoidant. Cubes avoid dry heat whenever possible. Some varieties appear to enjoy wet, tropical heat, but they avoid direct sunlight and none are known to inhabit arid deserts.

Weaponry

Melee 1. Grapple. Cubes enter occupied squares or lash out with their pseudopods to grapple opponents. While size Large cubes have a range of only 5′ with their pseudopods, Huge cubes have a range of 10′, and Gargantuan cubes extend their pseudopods 20′ and more. Grapple: Large +6, Huge +10, Gargantuan +16. PCs who fail grappling contests with cubes are engulfed. They take 6d6 acid damage at the start of each round until they escape with a STR Check: Large DC 12. Huge DC 16. Gargantuan DC 19.

Melee 2. Stunning Blow. Twice per combat, Cubes can choose to strike with their pseudopods from range or with their body mass in melee with a stunning blow. Damage: Large 3d6+2. Huge 5d6+5. Gargantuan 9d6+12. PCs struck by a stunning blow must Save DEX DC 14 or be knocked Prone.

Ranged 1. Spit Slime. Cubes can spit a slick slime to a range of 60′. This slime does no damage, but coats a 10′ square and makes it difficult to move through. PCs passing through affected squares must Save DC 14 DEX when moving normally, DC 18 DEX when Dashing, or fall Prone.

Ranged 2. Spit Acid. Twice per combat, cubes may spit their acid to range of 60′. This acid deals 3d6 damage.

Special Units

Crystal Cube. These cubes are extremely transparent and require a DC 17 WIS Check to see when they have not moved or attacked, even in daylight conditions. They tend to go into hiding while digesting their prey, then emerge when their mass has reclarified. They rarely grow above size Large.

Sable Cube. Sable cubes are shot through with dark coloring. They are easy to see in broad daylight, but extremely difficult to spot in shadowed environments, at night, and underground. Sable cubes require no Check to see in daylight, and a DC 18 WIS Check to see when they have not moved or attacked while in dark conditions. Sable cubes are slow movers and prefer cool, dark environments. They avoid direct sunlight unless fleeing from fire or other existential threat.

Shrieker. These cubes are known to emit blasts of sound similar to hollow, echoing shrieks. Those within 60′ must Save CON DC 14 of suffer -3 to STR for 1d4 rounds. Shriekers may use this sonic attack as an action twice per day.

Prismatic Cube. These chameleon cubes shift their coloring at will to blend with their environment. They requite a DC 17 WIS Check to see in all environments when they have not moved or attacked. They are especially likely to possess the special abilities Dancing Lights and Confuse (see below.)

Special Abilities

Eerie Mimic. Some cubes have the ability to make eerie sounds, often mimicking the sounds they hear in their habitats. Adventurers have reported hearing hollow voices mouthing strange words before an encounter with cubes. When a hidden cube uses this ability, PCs must make a DC 15 WIS Check to determine the true direction of the voice or sound.

Paralyze. Twice per day, cubes with this ability can paralyze their victims when they hit in combat. PCs must Save DC 14 CON or suffer from paralysis for 1d4 rounds. Cubes who have paralyzed their prey move to engulf and digest it as soon as they can.

Dancing Lights. Some cubes, especially Prismatic Cubes, are known to cast Dancing Lights, as per the spell, up to twice per day, to disorient their prey.

Confuse. Cubes size Huge and larger can befuddle their opponents with this psionic attack once per combat. PCs within 60′ must Save DC 15 WIS or 16 INT, or lose their next action. PCs who fail their Save by 6 or more must Save again. If they fail the second Save, they attack the nearest ally with their next action, before shaking off the effects of the confusion.

Movement

Run. Poor. Gelatinous Cubes move slowly and steadily along the ground, and do not tire. In warm, moist environments such as tropical jungles they can move as fast as a man for short distances..

Climb. Poor/Average. Cubes are poor climbers unless they have made themselves formless. While formless they can climb natural surfaces, even vertical cliffs. Their rate of ascent is slow.

Swim. Poor. Cubes do not swim in the classic sense, but they have been observed crossing rivers and lakes by navigating along the bottom. Rumors persist that some cubes are primarily aquatic, and even live in the oceans.

Burrow. Average. Cubes can quickly bury themselves in loose dirt and sand.

Fly. n/a

Grudges

Gelatinous Cubes do not hold grudges in the classic sense. They remember by smell those who have trespassed into their territories and escaped. They prioritize eating first those who are noisy, or who carry light or fire sources.

Gelatinous Cubes