Gelatinous Cube

Large ooze, unaligned

Armor Class
6
Hit Points
84
8d10 + 40
Speed
15 ft.
  • STR +2
  • DEX -4
  • CON +5
  • INT -5
  • WIS -2
  • CHA -5
Condition Immunities
blinded, charmed, deafened, exhaustion, frightened, prone
Senses
blindsight 60 ft. (blind beyond this radius), passive Perception 8
Challenge 2 450 XP · Proficiency +2

Traits

Ooze Cube

The cube takes up its entire space. Other creatures can enter the 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 can be seen but have Cover.

A creature within 5 feet of the cube can take an action to pull a creature or object out of the cube. Doing so requires a successful DC 12 Strength check, and the creature making the attempt takes 10 (3d6) acid damage.

The cube can hold only one Large creature or up to four Medium or smaller creatures inside it at a time.

Transparent

Even when the cube is in plain sight, it takes a successful DC 15 Wisdom (Perception) check to spot a cube that has neither moved nor attacked. A creature that tries to enter the cube's space while unaware of the cube is surprised by the cube.

Actions

Pseudopod

Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. 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 must make a DC 12 Dexterity saving throw.

On a successful save, the creature can choose to be pushed 5 feet back or to the side of the cube. A creature that chooses not to be pushed suffers the consequences of a failed saving throw.

On a failed save, the cube enters the creature's space, and the creature takes 10 (3d6) acid damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 21 (6d6) acid damage at the start of each of the cube's turns. When the cube moves, the engulfed creature moves with it.

An engulfed creature can try to escape by taking an action to make a DC 12 Strength check. On a success, the creature escapes and enters a space of its choice within 5 feet of the cube.

How to run it

Transparent is why this creature works: a DC 15 Perception check to spot one that has not moved, and a character who walks into it is surprised. Most gelatinous cube encounters begin with somebody already inside it.

Engulf then does 10 acid damage a round while the victim is blinded and restrained, and pulling them out needs a DC 12 Strength check that also hurts the rescuer. It is slow and stupid and cannot chase, so the whole fight is about the person inside.

Building the encounter

One for a party of four at level 3. It works best in a dungeon corridor where the party is moving carelessly, which is exactly the situation the creature evolved for in the fiction.

Give it a corridor rather than a room. Ooze Cube means it fills its space, so in a ten-foot passage it is a wall that must be dealt with rather than walked around.

What to pair it with

Nothing, generally. It is an environmental hazard with hit points, and adding creatures muddles that.

What pairs well is what is inside it. Half-dissolved equipment and a few coins suspended in the gel tells the party's story before they arrive, and gives them a reason to kill it rather than leave.

Reskins

A slow, invisible, engulfing hazard. Reflavour as a patch of living darkness, a sentient pool, an amoebic thing from another plane. Almost nothing about the fiction matters as long as the party cannot see it coming.

AC 6 is important and should stay. The cube is meant to be hit easily; the difficulty is that hitting it does not free the person inside.

Commonly played wrong

AC 6 means the party hits it essentially every time, and players sometimes read that as the encounter being trivial. It has 84 hit points, which at level 3 is several rounds of everyone attacking while a friend takes 10 acid damage a turn.

Engulfed creatures are blinded and restrained, not unconscious. They can still act, and a spellcaster inside a cube can still cast. Players forget this and give up their turns unnecessarily.

Compared to others at this CR

At CR 2 the cube has 84 hit points, more than the troll at CR 5, and does 10 damage a round to one target. It is the most durable and least threatening creature at its rating.

The ogre at the same CR will kill a character. The cube will scare one badly and cost the party a lot of time. Choose based on whether you want the fight to be dangerous or memorable.

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