D&D Creature Feature: Gelatinous Cubes

Personally, I have no idea how a seemingly simple 10ft large cube of acidic Jello became the D&D icon that it is, but Gelatinous Cubes can trace their origins all the way back to 1^st edition, where they haunted the 10x10 corridors of ubiquitous dungeons of Greyhawk and have appeared in every version of the game since. They are the founding member of the “Ooze” creature type, which is by far the smallest family in D&D, with only 4 entries in the 2014 Monster Manual and 6 in 2025. Slow-moving, a mere 15-foot speed, low CR 2, and so boring to look at that most people look right past them, they have somehow pseudopodded the hearts and minds of D&D fans with a PR campaign perhaps second only to that of the Owlbear. From Lego to the D&D movie, these featureless plate wobblers pop up continuously in campaigns, merch and memes. So! Let’s see how you can play them at your table.   

Gelatinous Cubes are not exactly what you call dynamic foes. Almost invisible unless they move, until they do it takes a DC15 Perception check to spot them and remember DMs, most of the time, these guys are skulking in dark dungeons. Unless they carry an open light source, even characters with Darkvision will be at disadvantage to spot them, as one of the most forgotten rules I feel comes into play here that characters with darkvision treat total darkness as Dim-Light, which is lightly obscured terrain, and therefore imposes disadvantage on sight-based checks. So keep that in your back pocket, especially as while Jelly Cubes have very poor Passive Perception at a measly 8, they also have blindsight to make up for it. Meaning, out to 60ft, they suffer no such penalty. Once they do move, they are AC6… which I believe is the lowest official creature AC in the game. Let me know if I’m wrong in the comments. They make up for this somewhat with a fairly beefy HP pool, but that has come down from 84 to 63 in the new rules. This was likely a tradeoff for a big improvement to their signature Engulf ability, which we will look at in a second. They are still immune to all the things you’d expect an amorphous blob of ooze to give zero fire-imps about, like Charm, Fear and the Prone conditions. The last defensive upgrade is an added immunity to acid damage… which I had to double check, as why the hell was this not already a thing?! I mean, the creature is literally a sentient beaker of hydrochloric acid that has dissolved too many dragon bones... but at least it is fixed now.

Switching to offence, and we have the closely related “Oooze Cube” and “Engulf” abilities. The main difference is that Ooze Cube is a passive ability for when a hapless creature wanders into the Jelly, whereas Engulf is used as an action to try to drag a nearby creature inside the acidic death blob by moving into the target's space. Both are DC12 DEX saves, but dopey creatures wandering into the Cube, having failed to spot it, have disadvantage. The nice little buff here that perhaps makes up for the lower HP is that Engulf in the 2025 Monster Manual now no longer triggers opportunity attacks, and a successful save by the target still takes half the damage of 3d6 acid and is bumped to the nearest unoccupied space. Whereas in 2014, on a success, you got off scot-free. This means each turn, a GC could move up to 30ft, not get swung at, and eventually swallow up to 4 medium or small PCs who get dragged along for the ride! It is also worth noting that if there is no unoccupied space to move to, the target automatically fails the check… keep that filed away for when we talk tactics.

Need a spot to hide your Cubes DM? :P

Once inside the cube, there is some nerfing relief for the unfortunate meal. The target is Restrained and takes automatic damage at the start of the Cube's turn, which was 6d6, which is DAMB scary, but now it is halved to 3d6, which brings the acidy average down from 21 to 10. PCs also begin to suffocate, but if you can't hold your breath longer than holding onto your skin, I’d be surprised. What is more significant is that the 2025 versions specifically calls out what was only implied in 2014, that this lack of oxygen prohibits the use of any spell with verbal components, making spellcasters less able to blast their way or misty step out from the inside. Keeping in mind, creatures reduced to 0HP auto fail a death save when taking damage, and you have precisely one chance to save your unconscious buddy trapped within the goo. How you do this is the same for either the trapped creature on its turn or a friendly PC who can attempt to extricate their friend on their own turn, a DC12 Strength Check. The good news for those being slowly dissolved is instead of the flat STR check of 2014, 2025 allows STR Athletics, which could often be higher. For their good Samaritan activities, the rescuer will, however, cop the 3d6 acid damage regardless of success, so… make it count! The only other action the GC has is a single pseudopod attack… but I can’t see any reason to ever use it unless it is already shifting a 4-pack of adventure tasty treats, and if that is so, we are already in TPK territory.

But how do you use this iconic creature to its full potential? Being super slow means once it is seen, it is an easy target to pick off at range, so it almost entirely relies on ambush tactics or clever placement. For me, GCs are nearly always part of some type of trap scenario, which restricts the players' manoeuvrability and brings their deadly Engulf ability to bear like a nice warm melty hug. Remember, while the DC for avoiding Engulf may not be high, you can rig it in your favour by limiting the space players have to move, such as in my ceiling Jelly falling into a 10x10x10 hole example with Kennymac in the intro of the video. A more classic and simple version of that trap is hiding the cube in the hole with treasure at the bottom. Have room doors lock, corridor portcullis slam down, and the GC ooze its way through the holes. In Dungeon of the Mad Mage, there was, Spoilers, a HUGE-sized jelly that filled a whole room. At a dungeon crossroads, have one pop out from each direction and force the adventurers to literally face a jelly sandwich dilemma as the cubes slowly approach from each side. Or, like our example with the slow-moving gibbering mouthers a few blogs ago, pair the GC up in an encounter with other small, fast-moving creatures like stirges, who can quickly engage the party so it has time to get into range.

The old 'Almost Invisible Gelatious Cube in a Pit with Shiny Things at the Bottom Trap' ... works (almost) EVERY time.

So while they may be featureless, slow, yet inexplicably attractive despite a Charisma score of 1, why not get an iconic cube or 4 into your next dungeon?  If your answer is, “Because James, I don’t have a miniature for them”, I have some good news: if you head over to my Patreon via this link and slide into the free membership tier, you can download a scaled paper mini of the Gelatinous Cube right now, along with every other monster featured on past and future Creature Features. I am still new to that platform and getting things sorted out, but for folks keen to flick me a few coppers a month, you’ll also gain access to more paper minis, spell cards, DM tools and monthly discounts on full products from the ZG back catalogue at Zalgariath.com. I hope to see you there as it grows and evolves.