Gelatinous Cube 5e: Engulf, Escape and Running the Cube

A gelatinous cube is a CR 2 Large ooze with AC 6, 84 hit points (63 in the 2024 rules) and a speed of only 15 feet. It barely fights. It rolls into your space, swallows you, and digests you while you can't breathe. Everything about the cube comes down to two traits: Transparent (a DC 15 Wisdom (Perception) check to notice a cube that hasn't moved) and Engulf (DC 12 Dexterity save or be trapped inside). The 2024 version deals half as much damage to engulfed creatures, is immune to acid, and stops engulfed characters from casting spells with a Verbal component.

Table of Contents

• •Gelatinous Cube Stat Block (2014)
• •Gelatinous Cube in the 2024 Rules
• •How Engulf Works, Step by Step
• •How the Gelatinous Cube Fights
• •Running a Gelatinous Cube Encounter
• •How Players Beat a Gelatinous Cube
• •Gelatinous Cube Encounter Ideas
• •Frequently Asked Questions

Gelatinous Cube Stat Block (2014)

The SRD 5.1 cube, identical to the 2014 Monster Manual version.

Read the stat block as a trap that moves. AC 6 means nearly every attack hits it, and Dexterity 3 gives it a −4 on Dexterity saves. What keeps it alive is Constitution 20 and 84 hit points, which is a lot for CR 2. Its only real attack, the 10-damage Pseudopod, is an afterthought. The 21 (6d6) acid damage an engulfed creature takes at the start of each of the cube's turns is the actual threat. That number alone drops most level 2 and 3 characters in two rounds.

It has blindsight out to 60 feet and is blind beyond it. Darkness, invisibility and silence do nothing to a cube that is already within 60 feet of you.

Gelatinous Cube in the 2024 Rules

SRD 5.2.1 keeps the cube's CR, AC, speed and Transparent trait, but rewrites Engulf.

The net effect: the 2024 cube is less lethal per victim but better at taking a whole party out of the fight. A level 3 character with 25 hit points who fails the save has taken 31 by the first acid tick from a 2014 cube, but 20 from a 2024 cube, so it is still conscious for its second escape attempt. Blocking Verbal spells means the engulfed cleric can't heal, and the engulfed wizard can't Misty Step out. The acid immunity shuts down Acid Splash and Acid Arrow, which work fine on the 2014 cube.

How Engulf Works, Step by Step

Engulf has more moving parts than any other CR 2 action. In order:

1. The cube uses its action to Engulf. It moves up to 15 feet. In 2014 it can enter the space of any Large or smaller creature. In 2024 it can only move through a creature's space if it has room inside for that creature (one Large or up to four Medium or Small creatures in total), and its movement doesn't provoke opportunity attacks.

2. Each creature whose space it enters makes a DC 12 Dexterity save. In 2024, a creature only saves the first time the cube enters its space during that move. A character with +2 Dexterity saves on 10 or higher, 55% of the time.

3. On a success:

• •2014: the creature takes no damage and chooses to be pushed 5 feet back or to the side. It can also refuse the push and be engulfed anyway (rarely useful, unless it wants to stay with a swallowed friend).
• •2024: the creature takes half damage (about 5) and moves to an unoccupied space within 5 feet of the cube. If no such space exists, it fails the save instead. In a 10-foot corridor with the party packed behind the front rank, the only open spaces may be on the cube's far side, where it came from. A successful save there still cuts the character off from the party. In a dead end or a crowded room, there may be no open space at all.

4. On a failure: 10 (3d6) acid damage, and the creature is engulfed. It is Restrained (attacks against it have advantage, its attacks have disadvantage, its Dexterity saves have disadvantage), it moves with the cube, and it has total cover from everything outside. In 2024 it also can't cast spells with a Verbal component.

5. Damage over time. At the start of each of the cube's turns, every engulfed creature takes 21 (6d6) acid in 2014 or 10 (3d6) acid in 2024. The engulfed creature acts between the swallow and the first tick, so it gets one escape attempt before that damage lands.

6. Getting out.

• •From inside: use an action and make a DC 12 Strength check (2024: Strength (Athletics)). A character with +3 on the check succeeds on 9 or higher, 60%. One with −1 succeeds on 13 or higher, 40%. On a success you exit to a space of your choice within 5 feet (2014) or the nearest unoccupied space (2024).
• •From outside: a creature within 5 feet of the cube uses an action and makes the same DC 12 check to pull someone (or an object) out. The rescuer takes 10 (3d6) acid damage whether or not it succeeds.

7. Walking into it. A creature that enters the cube's space voluntarily or by accident is hit by Engulf and makes the save with disadvantage. With disadvantage, that +2 Dexterity character saves only about 30% of the time. In 2014, a creature that steps into an unnoticed cube is also surprised.

About breathing. The 2014 cube says the engulfed creature "can't breathe". Under the SRD 5.1 suffocation rules it can hold its breath for 1 + its Constitution modifier minutes (minimum 30 seconds); after that it survives rounds equal to its Constitution modifier (minimum 1) and then drops to 0 hit points.

The 2024 cube says the engulfed creature "is suffocating". SRD 5.2.1 defines Suffocation as a hazard: a creature can hold its breath for 1 + its Constitution modifier minutes (minimum 30 seconds) before suffocation begins. Once it runs out of breath, it gains 1 Exhaustion level at the end of each of its turns, and it removes all of those levels when it can breathe again. Read against that definition, the engulfed creature starts holding its breath when swallowed. Even the 30-second minimum is 5 rounds, so in most fights the acid matters long before the air does.

DM ruling, not rules text: some DMs read "is suffocating" as "already out of breath", so the victim gains Exhaustion at the end of every turn inside. That is much harsher than the glossary definition. If you use it, tell the players before the session, not mid-fight.

How the Gelatinous Cube Fights

A cube has Intelligence 1. It doesn't plan. It moves toward food, engulfs, and keeps moving. The danger comes from where you put it.

Corridors are its home. A Large cube fills a 10-foot-wide corridor wall to wall. Nothing gets past it, and with a 15-foot Engulf move it can swallow the front rank of a party that is marching two abreast. Under the 2024 rules, a front-rank character with allies directly behind it and walls to both sides can only dodge to the cube's far side, alone, and in a dead end it has nowhere to go and fails the save automatically.

Swallow, then retreat. With a victim inside, the cube's best play is to keep moving away from the rest of the party. The engulfed creature moves with it, so the rescuers have to chase a slow but solid wall of acid. Every turn the cube spends out of reach is another 21 (or 10) damage to its passenger.

Engulf beats Pseudopod almost every round. Compare a 2014 cube's options against a character with AC 16:

The pseudopod only matters when there is nobody left to swallow, or when the cube is full.

Let it be found. The cube is at its worst when the party sees it first. Players can walk backward at 30 feet and shoot it to death while it crawls toward them at 15. Put it somewhere that removes the walk-away option: a dead-end, a corridor behind a door, a pit bottom, the far side of a portcullis that just dropped.

The ambush. A motionless cube in a dim corridor takes a DC 15 Perception check to notice. Most level 2 characters have a passive Perception between 10 and 14, so an unnoticed cube is the default. In 2014, a creature that walks into an unnoticed cube is surprised and makes its save at disadvantage. In 2024, if the cube starts the fight unnoticed, the party is surprised and rolls initiative with disadvantage.

Running a Gelatinous Cube Encounter

The cube is a CR 2 creature worth 450 XP. For four characters under the 2024 SRD 5.2.1 budget:

Good level 3 builds within the Moderate 900 XP: one cube plus an ochre jelly (450 XP each), or one cube plus a gray ooze and some zombies pushed into the party from the other side.

Under the 2014 Dungeon Master's Guide thresholds, which our encounter difficulty calculator applies, one cube against four level 2 characters is a Medium fight (450 XP against a 400 Medium threshold). XP doesn't capture a cube well, though. In the open it's an easy kill. In a corridor with surprise, the 2014 cube can kill a level 2 character outright: 10 on the swallow plus 21 at the start of its next turn is 31 damage, more than most level 2 characters have.

Rules of thumb:

• •The 2014 cube is a level 3+ monster in practice. Use the 2024 cube if you want it at level 2.
• •One cube is a corridor event, not a boss fight. It works best as an interruption during another encounter.
• •Put loot inside it. Coins, a key, a sword and some bones visible through the jelly give the party a reason to fight it instead of walking away.

How Players Beat a Gelatinous Cube

Don't let it reach you. Its speed is 15 feet. A party that spots it first can back away and attack every turn. Ranged weapons and cantrips will kill it: at AC 6, a +5 attack only misses on a natural 1.

Spot it. Light, a familiar scouting ahead, or a ten-foot pole poked into the corridor all reveal a cube. Characters with high passive Perception should walk in front.

Hit its Dexterity. It has a −4 Dexterity save and no resistances in 2014. Fireball deals 28 on average on a failed save, a third of the 2014 cube's hit points. Burning Hands also targets Dexterity. Skip Constitution-save spells: the cube's +5 there is its best save. Be careful with area spells once a friend is inside it: the DM may rule the blast reaches them.

Don't waste these: Acid damage against the 2024 cube (immune). Charm, fear and blindness effects (it is immune to charmed, frightened and blinded in both editions). Knocking it prone (immune). Invisibility within 60 feet (blindsight).

If someone gets engulfed:

• •The engulfed creature should try to escape on its own turn. The strongest character pulls from outside (action, DC 12 Strength check, costs 3d6 acid).
• •You can't target someone inside the cube with a spell like Cure Wounds or Healing Word because they have total cover. Heal them after they're out, or kill the cube.
• •Often the fastest rescue is a dead cube. With 63 HP in 2024, a focused party of four at level 3 can usually burn it down in two or three rounds.

Restrain or hold it. It has no immunity to Restrained or Paralyzed. Entangle targets Strength saves, where the cube has only +2. A Restrained cube has a speed of 0, so it can't use Engulf to move into anyone new. Anyone already inside still takes the acid, so get them out.

Gelatinous Cube Encounter Ideas

The museum guard. A wizard's old vault uses a cube as its cleaner. The cube follows a fixed route through the corridors every hour and has 40 years of failed thieves' gear suspended inside: daggers, a lantern, a full set of thieves' tools, a signet ring. Smart players can time its route and slip past. Greedy ones go fishing.

The flooded stairwell. A spiral stair descends into a pool of still water. The water is clear and the bottom looks 10 feet down. The bottom is actually the top of a cube sitting in a narrow shaft. Anyone who jumps in falls into its space. The fix is a rope and a rescue roll, and the treasure is whatever it ate on the way down.

Two cubes, one corridor. The party fights something at a corridor junction. On round three, a cube enters from the passage behind them, slowly. On round five, another arrives from the side passage. The fight in front is now on a clock, and the party has to decide who holds the rear and who finishes the main threat.

If your campaign has a dungeon full of cubes and the party keeps losing gear inside them, Loreify's session notes can track who lost what and where.

Frequently Asked Questions

What CR is a gelatinous cube?

A gelatinous cube is CR 2 (450 XP) in both the 2014 and 2024 rules. It has AC 6, a speed of 15 feet, and 84 hit points in 2014 or 63 in 2024.

How do you escape a gelatinous cube in 5e?

Use your action and make a DC 12 Strength check (Strength (Athletics) in 2024). On a success you leave the cube. An ally within 5 feet can also pull you out with an action and the same DC 12 check, but the ally takes 10 (3d6) acid damage.

How much damage does a gelatinous cube do?

Engulf deals 10 (3d6) acid damage when it swallows a creature. After that, an engulfed creature takes 21 (6d6) acid at the start of each of the cube's turns in 2014, or 10 (3d6) in 2024. Its Pseudopod deals 10 (2014) or 12 (2024) acid.

Can you see a gelatinous cube?

It is transparent. Noticing a cube that hasn't moved or acted takes a successful DC 15 Wisdom (Perception) check, even when it is in plain sight. Creatures inside it are visible but have total cover.

Is a gelatinous cube immune to acid?

Only in the 2024 rules. The 2014 cube has no damage immunities, so acid spells work on it. Both versions are immune to the blinded, charmed, deafened, exhaustion, frightened and prone conditions.

Can you cast spells while engulfed by a gelatinous cube?

In the 2024 rules, an engulfed creature can't cast spells with a Verbal component. The 2014 stat block has no such restriction, though the engulfed caster is Restrained and has disadvantage on attack rolls, including spell attacks.

Stat blocks: System Reference Document 5.1 (2014) and 5.2.1 (2024), Wizards of the Coast, CC-BY-4.0. Tactics, encounter math and ideas are Loreify's own.