Gelatinous Cube

Gelatinous Cube

Large ooze · CR 2 · 450 XP

6 AC · 63 HP

Roll the Gelatinous Cube

Pseudopod
Engulf DC 12 DEX

Press a roll button. The dice land here.

The Gelatinous Cube is the thing nobody looked for

How to run it. AC 6, 63 Hit Points, Speed 15. Almost anything hits it: a +5 attack lands 95% of the time. Its danger is not the fight but the first moment. Unless someone saw it move, noticing it takes a DC 15 Wisdom (Perception) check. A character with +2 makes that 40% of the time.

Engulf. It moves into creatures' spaces without provoking. Each makes a DC 12 Dexterity save: with +0, 55% fail; walk into it unaware, with Disadvantage, and 80% fail. Failing means 3d6 Acid, then Restrained, suffocating, no Verbal spells, and another 3d6 at the start of each of the cube's turns. Two turns inside after a failed save is about 31 damage on average.

Getting out. An action and a DC 12 Strength (Athletics) check. A fighter with +5 escapes 70% of the time; a wizard with −1, 40%. A friend outside can pull someone free with the same check, and takes 3d6 Acid for the favour.

The choice that matters is where you put it. A 10-foot corridor it fills wall to wall is the classic, because the party walks into it. Give a clue with no alarm attached: a clean floor where the rest is dusty, bones hanging at knee height.

The common mistake is describing it. "The corridor ahead is clear" is enough. If you describe the air as shimmering, you told them.

For players. Poke the dark with a 10-foot pole, or a thrown copper. Keep the wizard out of the front rank; a Restrained, suffocating caster with no Verbal spells has nothing.

The human angle. Simons and Chabris asked people to count basketball passes, and about half missed a person in a gorilla suit walking through the scene. Attention filters out what we don't expect. The cube is transparent, but the real reason it works is that nobody expects a hallway to be a monster.

Source: Simons, D. J., & Chabris, C. F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception, 28(9), 1059–1074. doi:10.1068/p281059

Stat block

Type
Large ooze, unaligned
Armor Class
6
Hit Points
63 (6d10 + 30)
Speed
15 ft.
Challenge
2 (450 XP), proficiency +2
Immunities
acid
Condition immunities
Blinded, Charmed, Deafened, Exhaustion, Frightened, Prone
Senses
blindsight 60 ft., passive perception 8
Languages
None
STRDEXCONINTWISCHA
14
3
20
1
6
1

Gelatinous Cube odds against your Armor Class

Chance to hit, then average damage per attack once misses and critical hits are counted.

AttackAC 12AC 14AC 15AC 16AC 18AC 20
Pseudopod (+4)65%
8.7 dmg		55%
7.4 dmg		50%
6.8 dmg		45%
6.2 dmg		35%
4.9 dmg		25%
3.7 dmg

Gelatinous Cube hit points

The stat block uses the average, 63. Rolled, 6d10 + 30 lands anywhere from 36 to 90.

36: 0.00%37: 0.00%38: 0.00%39: 0.01%40: 0.01%41: 0.03%42: 0.05%43: 0.08%44: 0.13%45: 0.20%46: 0.30%47: 0.43%48: 0.61%49: 0.82%50: 1.09%51: 1.40%52: 1.76%53: 2.16%54: 2.59%55: 3.05%56: 3.51%57: 3.97%58: 4.39%59: 4.77%60: 5.09%61: 5.33%62: 5.47%63: 5.53%64: 5.47%65: 5.33%66: 5.09%67: 4.77%68: 4.39%69: 3.97%70: 3.51%71: 3.05%72: 2.59%73: 2.16%74: 1.76%75: 1.40%76: 1.09%77: 0.82%78: 0.61%79: 0.43%80: 0.30%81: 0.20%82: 0.13%83: 0.08%84: 0.05%85: 0.03%86: 0.01%87: 0.01%88: 0.00%89: 0.00%90: 0.00%
36chance of each total for 6d10 + 3090
Hit pointsChance
50 or more97%
63 or more53%
77 or more3%
85 or more<1%

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 () 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 () 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 () 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 () 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.

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This page includes material from the System Reference Document 5.2.1 (“SRD 5.2.1”) by Wizards of the Coast LLC, available at dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License. The averages, odds and tables are ours.