Friday Encounter: Cube in a Bottle

Thinking about my recent ruminations on second-string D&D monsters, I do need to give an honorable mention to gelatinous cubes. I didn't include them in the last post because I wouldn't exactly call them underused, and let's be honest, they are pretty silly. I might've made a case for cloakers, but I don't know if I can make gelatinous cubes cool. They're just inherently kind of ridiculous. But I love them all the same. Their inclusion in the 3e starter set that introduced me to the game (complete with a little cardboard gelatinous cube counter for the map) stuck in my mind, introduced me to the word gelatinous, and cemented gelatinous cubes as a running joke in my family for years, to the point where I was very confused when a gelato restaurant opened near me later on. One of the ways this manifested in one of my early games was an encounter I saw fit to revisit for my column.

Cube in a Bottle

This encounter can be used in most environments. It could be dropped in a dungeon room or encountered along the side of the road in an overturned cart, in the wilderness in an abandoned cabin, or in a town in some back alley or run-down house the party decided to tresspass in. The important part is that the PCs should find two items - an old journal, and a strange potion bottle.

The journal details the experiment log of an alchemist, describing how the author scraped some slime off the wall of a cave into the bottle and dropped table scraps into it over a couple of days. As time passed, the slime grew and grew until it began to fill the dimensions of the bottle. The journal notes that this must be a step toward the ultimate pursuit of alchemy - the creation of life! However, the log abruptly ends after a few entries. The reason why is up to you - perhaps something nefarious happened, or the alchemist was a victim of their own curiosity, or perhaps they simply lost their work and are looking for it now...

The bottle, meanwhile, is completely filled with a transparent viscous substance. It might be mistaken for being empty, but is heavier than an empty bottle should be, and is corked with a copper plug. Careful investigation will note that the side of the stopper inside the bottle appears green, like it's corroded.

If watched closely (DC 15 Perception check), one might observe that the fluid inside the bottle seems to slowly slosh back and forth on its own, as though it's alive! A DC 15 Nature check, furthermore, will determine that the bottle contains a gelatinous cube that has grown to fill the dimensions of the bottle rather than those of a dungeon corridor. This check is made with Advantage if the creature making the check previously read the alchemist's journal.

If a creature consumes the contents of the bottle, they must make a DC 12 Constitution save. On a failed save, the thick texture of the cube is so repugnant that they vomit out the contents, preventing further harm but giving them Disadvantage on attack rolls and ability checks for the next hour. On a successful save, the creature is able to supress their gag reflex enough to swallow the cube...which is worse.

Enter Action Time if this happens; also roll initiative for the cube, but it cannot take normal actions at first. Every round, the cube will grow inside the victim's digestive tract, dealing 3d6 acid damage and 3d6 force damage at the start of its turn.

After 1d4+1 rounds, the cube begins to expand from the victim's mouth, during which it can be targeted and can make attacks with its pseudopods (it cannot engulf creatures in this state). If damaged, the cube takes half damage (rounded down) and the victim takes the other half. Note that the cube will not be hostile toward creatures other than the victim until it is attacked by them.

A cure disease or similar spell will automatically expel the cube from the victim's body, but it will remain hostile to the victim and to any creatures that attack it. If the victim dies while the cube is growing inside of it, the cube explodes from its body violently and expands to its full size over the course of 1d4 minutes.

Alternatively, if the bottle is opened and the contents dumped out, the cube will expand to its full size as above. If not attacked, it will be largely indifferent toward the creatures that freed it and will continue on its business doing gelatinous cube things unless interacted with (with hostility or otherwise). A party that provides the cube with food may be able to make an ally of it...though it is wise to keep it sated, lest it go after them instead!