Gelatinous Cube
- Size: Large
- Type: Ooze
- Alignment: Unaligned
- AC: 6
- Initiative: -4 (6)
- HP: 63 (6d10+30)
- Speed: 15 ft
| ATTR | VAL | MOD | SAVE |
|---|---|---|---|
| STR | 14 | +2 | +2 |
| DEX | 3 | -4 | -4 |
| CON | 20 | +5 | +5 |
| 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
- Languages: None
- CR: 2 (XP 450; PB +2)
Traits
Ooze Cube. The cube fills its entire space and is transparent. Other creatures can enter that space, but a creature that does so is subjected to the cube's Engulf and has Disadvantage on the saving throw.
Creatures inside the cube have Total Cover, and the cube can hold one Large creature or up to four Medium or Small creatures inside itself at a time.
As an action, a creature within 5 feet of the cube can pull a creature or an object out of the cube by succeeding on a DC 12 Strength (Athletics) check, and the puller takes 10 (3d6) Acid damage.
Transparent. Even when the cube is in plain sight, a creature must succeed on a DC 15 Wisdom (Perception) check to notice the cube if the creature hasn't witnessed the cube move or otherwise act.
Actions
Pseudopod. Melee Attack Roll: +4, reach 5 ft. Hit: 12 (3d6+2) Acid damage.
Engulf. The cube moves up to its Speed without provoking Opportunity Attacks. The cube can move through the spaces of Large or smaller creatures if it has room inside itself to contain them (see the Ooze Cube trait). Dexterity Saving Throw: DC 12, each creature whose space the cube enters for the first time during this move. Failure: 10 (3d6) Acid damage, and the target is engulfed. An engulfed target is suffocating, can't cast spells with a Verbal component, has the Restrained condition, and takes 10 (3d6) Acid damage at the start of each of the cube's turns. When the cube moves, the engulfed target moves with it. An engulfed target can try to escape by taking an action to make a DC 12 Strength (Athletics) check. On a successful check, the target escapes and enters the nearest unoccupied space. Success: Half damage, and the target moves to an unoccupied space within 5 feet of the cube. If there is no unoccupied space, the target fails the save instead.
Lore & Background
Gelatinous cubes are among the most feared and efficient dungeon cleaners in existence, massive oozes that have evolved to perfectly fit within the corridors of ancient ruins and underground complexes. These translucent, cube-shaped creatures move slowly but inexorably through passages, dissolving and consuming everything organic in their path. They serve as nature's ultimate recycling system, breaking down dead matter and maintaining the ecosystem of underground environments.
Created through magical experimentation or spontaneous generation in areas rich with magical energy, gelatinous cubes have become synonymous with dungeon exploration. Their perfect cubic shape allows them to navigate corridors with mechanical precision, while their transparent nature makes them nearly invisible until it's too late. Many adventurers have met their end by walking directly into these patient predators.
Combat Tactics
Gelatinous cubes rely on their Transparent nature to remain undetected until prey walks directly into them. Once combat begins, they use their Engulf ability to swallow entire creatures, subjecting them to ongoing acid damage while preventing them from breathing. Engulfed creatures can attack the cube from within, but must succeed on ability checks to escape.
The cube's Pseudopod attacks can paralyze victims, making them easier to engulf on subsequent turns. Their Ooze Cube nature makes them immune to many conditions and allows them to squeeze through spaces as narrow as 1 foot wide, despite their large size. They are particularly dangerous in narrow corridors where escape is difficult.
Encounter Ideas
The Cleaning Crew: A wealthy noble has hired a wizard to use gelatinous cubes to 'clean' his dungeon of unwanted monsters, but the cubes have grown beyond their intended size and now threaten to escape into the manor above.
Transparent Trap: A gelatinous cube has positioned itself in a doorway between two rooms, creating an invisible barrier that dissolves anyone trying to pass through. The party must find an alternative route or a way to detect and defeat the creature.
The Curator's Collection: A gelatinous cube in an ancient library has been 'preserving' books and scrolls within its body for centuries, creating a mobile archive of knowledge that the party needs to access without destroying.
Dungeon Maintenance: The party discovers that a complex of ruins is kept clean and functional by a family of gelatinous cubes that have been fulfilling their purpose for generations, raising questions about whether they should be destroyed or left to continue their work.
Environmental Effects
Gelatinous cubes leave behind perfectly clean corridors and chambers, having dissolved all organic matter in their path. Stone surfaces appear polished and gleaming, while metal objects may show signs of acid etching. The air in areas frequented by gelatinous cubes often has a sharp, acidic smell.
Floors in cube territory are typically free of debris, dust, and organic matter, creating unnaturally clean pathways through otherwise ancient ruins. Walls may show acid damage at cube height, creating distinctive horizontal scarring patterns.
Treasure
Gelatinous cubes inadvertently serve as treasure repositories, as inorganic items consumed by the cube remain suspended within its body. Coins, gems, jewelry, and magic items can often be seen floating within the creature's transparent form, creating a tantalizing but dangerous treasure display.
Weapons and armor may be partially dissolved but still functional, while books and scrolls are typically destroyed unless they have magical protection. The cube's body might contain decades or even centuries worth of accumulated treasure from its victims.
Plot Hooks
The Living Vault: A gelatinous cube has been used as a mobile treasure vault by a criminal organization, with the cube trained to regurgitate specific items on command. The party must find a way to access the treasure without becoming the cube's next meal.
Dungeon Ecology: Scholars studying dungeon ecosystems have discovered that gelatinous cubes play a crucial role in maintaining the balance of underground environments. The party must protect a cube from those who would destroy it, despite its dangerous nature.
The Transparent Witness: A gelatinous cube has absorbed the remains of a murder victim, and divination magic reveals that the cube somehow retains the victim's final memories. The party must find a way to extract this information to solve the crime.
Cube Cultivation: A mad alchemist has been breeding gelatinous cubes in different sizes and colors, each with unique properties. Some cubes preserve rather than dissolve, others move at different speeds, and the party must navigate this dangerous laboratory of experimental oozes.