AC 6
HP 76 (8d10 + 32; bloodied 38)
Speed 15 ft., swim 15 ft.
Proficiency +2; Maneuver DC 13
Condition Immunities blinded , charmed , deafened , fatigue , frightened , prone
Senses blindsight 60 ft. (blind beyond this radius), passive Perception 8
Languages —
Engulfing Body. A creature that enters the cube’s space is subjected to the saving throw and consequences of its Engulf attack.
Sunlight Sensitivity. While in sunlight, the cube has disadvantage on attack rolls .
Transparent. While the cube is motionless, creatures unaware of its presence must succeed on a DC 15 Perception check to spot it.
Ooze Nature. An ooze doesn’t require air or sleep.
ACTIONS
Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (3d6) acid damage.
Engulf. The cube moves up to its Speed. While doing so, it can enter Large or smaller creatures’ spaces. Whenever the cube enters a creature’s space, the creature makes a DC 13 Dexterity saving throw . If the creature is unaware of the cube’s presence, it makes its saving throw against Engulf with disadvantage . On a success, the creature may use its reaction, if available, to move up to half its Speed without provoking opportunity attacks . If the creature doesn’t move, it is engulfed by the cube.
A creature engulfed by the cube takes 10 (3d6) acid damage, can’t breathe , is restrained , and takes 10 (3d6) acid damage at the start of each of the cube’s turns. It can be seen but has total cover . It moves with the cube. The cube can hold as many creatures as fit in its space without squeezing.
An engulfed creature can escape by using an action to make a DC 13 Strength check. On a success, the creature moves to a space within 5 feet of the cube. A creature within 5 feet can take the same action to free an engulfed creature, but takes 10 (3d6) acid damage in the process.
Combat
The cube moves constantly, stopping only when its blindsight detects moving creatures. It then waits motionless for creatures to blunder into it. It pursues creatures that move away from it, either Dashing or using the extra movement from its Engulf action. It retreats only if it’s full (containing four Medium creatures or one Large creature) or if it’s exposed to sunlight.
Legends and Lore
With an Arcana or Nature check, characters can learn the following:
DC 10 Mindless and able to squeeze through the narrowest of cracks, oozes inhabit dank, dark places all over the world.
DC 15 There are many different types of oozes. Perhaps the strangest is the gelatinous cube: a nearly transparent ooze that engulfs dungeon explorers who stumble into it.
DC 20 Oozes dissolve any organic matter they come into contact with. Some oozes, such as black puddings, corrode metal as well.
Some believe gelatinous cubes are merely a myth perpetuated by adventurers, but gelatinous cubes are very real. These improbable organisms are literally shaped by their hunting grounds. Gelatinous cubes squared by decades of patrolling dungeon corridors are most common. However, gelatinous cubes that spend years squeezing through sewer tunnels may become gelatinous tubes, while those that waft through underwater caves resemble gelatinous bubbles.
Whatever its shape, a gelatinous cube is as transparent as a pane of glass, and unlucky prey may blunder right into it. A gelatinous cube that’s still digesting a meal is easier to spot, as inedible materials like metal, wood, and bone remain suspended inside the cube and appear to float in midair.
1–2 DC 13 Perception check: pristine floors or walls
2 A door missing its metal hinges (gray ooze), a door missing its lower half (black pudding), or a skeleton (gelatinous cube or ochre jelly)
3 A bit of writhing ooze stuck in a crack
4 Wet and dripping walls and floors. DC 14 Investigation or Survival: The area is completely free of lichen, fungus, and other life that might thrive in this environment
Oozes lurk in sunless areas such as caverns, dungeons, and the ocean depths, as well as in areas of the Abyss and the Bleak Gate.
CR 0–2 gelatinous cube ; ochre jelly ; 1 to 3 gray oozes ; gray ooze in pit trap
Treasure flat carnelian gem carved with a lion, possibly once part of a signet ring (75 gp)
CR 3–4 black pudding ; gelatinous cube in pit trap; 2 gelatinous cubes or ochre jellies ; ochre jelly with 1d4 flying swords
Treasure flint, chalk, marble chess pieces (125 gp), malachite gem (10 gp), 1 dagger enchanted with continual flame
CR 5–10 elder black pudding ; gelatinous wall ; black pudding with walking statue or mimic
Treasure 3 sealed wine bottles containing fine wine (100 gp each), 4 amethyst gemstones (100 gp each), 2 elemental gems (fire)
Oozes are ambulatory, predatory amoeboid creatures that infest caverns and other dark places. A gelatinous cube is an ooze.