Gelatinous Cubes¶
Acidic, Nigh-Invisible Dungeon Cleaner
A Gelatinous Cube is a silent, quivering mass of acidic goo that dissolves any organic material unfortunate enough to get caught inside. These cubes glide slowly and silently through dungeons, caverns, and other forgotten caverns, with eeie purpose, as if some deeper instinct compels their mindless patrol.
Unless it's recently dined, a gelatinous cube is nearly invisible. Many a would-be hero has walked directly into one, only to add their gear to the cube's collection. Over decades, cubes expand to fill available space, with some ancient cubes reaching tremendous sizes.
From classic D&D dungeons to modern 5E campaigns, Gelatinous Cubes remain a deadly, near-invisible menace waiting to engulf unwary adventurers.
Gelatinous Cube Lore¶
- Gelatinous Cubes glide toward their prey without hesitation, as if guided by some deeper mysterious instinct
- Once engulfed, escape is rare. The cube immediately begins digesting its prey
- The contents of a cube often include more than bones: half-dissolved scrolls, rusted crowns, or the final relics of an unlucky party.
Gelatinous Cube Tactics¶
Gelatinous Cubes are mindless entities driven to absorb any organic matter in their path. The cube simple dashes towards the largest concentration of foes that it can sense.
Gelatinous Cube Statblocks¶
Gelatinous Cube¶
Gelatinous Cube
Summoned with Foe FoundryLarge Ooze (Gelatinous Cube)
AC 6 Initiative +0 (10)
HP 63 (6d10 + 30)
Speed 20 ft., climb 20 ft.
| Mod | Save | ||
|---|---|---|---|
| Str | 14 | +2 | +2 |
| Dex | 3 | -4 | -4 |
| Con | 20 | +5 | +5 |
| Mod | Save | ||
|---|---|---|---|
| Int | 1 | -5 | -5 |
| Wis | 6 | -2 | -2 |
| Cha | 1 | -5 | -5 |
Immunities Acid; Blinded, Charmed, Deafened, Exhaustion, Frightened, Prone
Senses Blindsight 60 ft., Passive Perception 8
CR 2 (450 XP; PB +2)
Traits
Transparent. Even when the gelatinous cube is in plain sight, it takes a successful DC 15 Perception check to spot the gelatinous cube if it has neither moved nor attacked. A creature that tries to enter the gelatinous cube's space is surprised by the gelatinous cube.
Actions
Pseudopod. Melee Weapon Attack: +4 to hit, reach 5ft., one target. Hit 16 (4d6 + 2) acid damage.
Engulf in Ooze.
The gelatinous cube moves up to its speed and can enter Large or smaller creature's spaces. When it enters a creature's space, that creature must make a DC 12 Dexterity save. The save is made at disadvantage if the target is unaware of the cube, and automatically fails if there is no nearby unoccupied space.
On a failure, the creature takes 10 (4d4) acid damage and is Engulfed. A creature that is Engulfed is Restrained, Suffocating, and cannot cast spells with Verbal components. It takes 10 (4d4) ongoing acid damage at the end of each of its turns. It can spend an Action to make a DC 12 Athletics check to escape the engulfing creature.
Bonus Actions
Metabolic Surge. If the gelatinous cube has at least 2 creatures Engulfed then it gains 10 temporary hit points.
Ancient Gelatinous Cube¶
An Ancient Gelatinous Cube has absorbed so much organic material that it has swollen to tremendous size. Some are rumored to contain entire treasure hoards from the assortment of misfortunate adventurers they have absorbed over the decades.
Ancient Gelatinous Cube
Summoned with Foe FoundryHuge Ooze (Gelatinous Cube)
AC 6 Initiative +2 (12)
HP 161 (14d12 + 70)
Speed 20 ft., climb 20 ft.
| Mod | Save | ||
|---|---|---|---|
| Str | 16 | +3 | +3 |
| Dex | 3 | -4 | -4 |
| Con | 20 | +5 | +5 |
| Mod | Save | ||
|---|---|---|---|
| Int | 1 | -5 | -5 |
| Wis | 7 | -2 | -2 |
| Cha | 1 | -5 | -5 |
Immunities Acid; Blinded, Charmed, Deafened, Exhaustion, Frightened, Prone
Senses Blindsight 60 ft., Passive Perception 8
CR 6 (2,300 XP; PB +3)
Traits
Deadly Ambusher. On the first turn of combat, the gelatinous cube has advantage on any attack rolls against targets with lower initiative than it, and it scores a critical hit on a score of 19 or 20.
Transparent. Even when the gelatinous cube is in plain sight, it takes a successful DC 15 Perception check to spot the gelatinous cube if it has neither moved nor attacked. A creature that tries to enter the gelatinous cube's space is surprised by the gelatinous cube.
Actions
Multiattack. The gelatinous cube makes two Pseudopod attacks. It may replace one attack with a use of its Engulf in Ooze.
Pseudopod. Melee Weapon Attack: +6 to hit, reach 5ft., one target. Hit 20 (5d6 + 3) acid damage.
Engulf in Ooze.
The gelatinous cube moves up to its speed and can enter Large or smaller creature's spaces. When it enters a creature's space, that creature must make a DC 14 Dexterity save. The save is made at disadvantage if the target is unaware of the cube, and automatically fails if there is no nearby unoccupied space.
On a failure, the creature takes 15 (6d4) acid damage and is Engulfed. A creature that is Engulfed is Restrained, Suffocating, and cannot cast spells with Verbal components. It takes 15 (6d4) ongoing acid damage at the end of each of its turns. It can spend an Action to make a DC 14 Athletics check to escape the engulfing creature.
Slime Spray (Recharge 6). The gelatinous cube sprays slimy goo in a 30-foot cone. Each creature in that area must make a DC 12 Dexterity saving throw. On a failure, the creature takes 30 (12d4) acid damage and is Grappled (escape DC 12). On a success, the creature takes half as much damage instead.
Bonus Actions
Metabolic Surge. If the gelatinous cube has at least 2 creatures Engulfed then it gains 30 temporary hit points.
Gelatinous Cube Encounter Ideas¶
- A panicked NPC barrels past the party, screaming about something hunting them. Before anyone can react, they run headfirst into what looks like empty space and vanish mid-sprint into a Gelatinous Cube.
- A gleaming sword glows softly as it floats toward the party, gripped by the skeletal hand of a long-dead adventurer. It’s only when the bones bob and twist that the party notices the faint shimmer. The sword (and its former owner) are suspended inside a Gelatinous Cube.
- An ancient Revenant is forever trapped inside a Gelatinous Cube. Half disolved, it reaches toward the party and implores with gestures to be freed. It wishes only to continue its quest to hunt down those that wronged it.
- A droplet hits a character’s cheek with a soft hiss. Above them, the ceiling glistens and begins to descend. One or more Gelatinous Cubes cling to the ceiling, melting downward like slow, acidic raindrops.
Gelatinous Cube Adventure Ideas¶
- A fast-talking Mage hires the party to capture a Gelatinous Cube alive — "For purely academic reasons, of course." She provides a suspiciously unstable containment field and dubious advice like "Try not to get engulfed."
- A wealthy Noble hires the party to rescue his daughter’s rookie adventuring group from a nearby dungeon. Inside, the halls are strangely clean with just a faint acidic scent revealing the work of one or more Gelatinous Cube. The daughter's bracelet floats, undisolved, inside one of the cubes.
- An overconfident alchemist hires the party to "field-test" a new Ooze-Dissolving Draught™. When thrown at the Gelatinous Cube, it causes it to bubble, shimmer, and suddenly grow in size and transform into an Ancient Gelatinous Cube
- The party has been hired to recover lost treasure of an eccentric mage. The mage created a special vault and enchanted an Ancient Gelatinous Cube to store the treasure within its gloopy body.