In my last session, my players ran into a gelatinous cube. Well, encountered. It would have been funny if they actually ran into it, of course.
Everyone identified it pretty quickly. Dryst's player knew it well enough to list its probable powers. But a couple guys said "I never actually ran into one."
Iconic old-school monster. A killer 10 x 10 x 10 foot cube of dungeon-clearing "so this is why stuff we leave behind is gone" monster.
But they never ran into it.
Heck, I rarely used them myself.
I think part of this is that they are so iconic, so obvious, and so well-known that they are hard to use. You either feel they're overused, or too obvious, or that they are so special you need to save them up for a special occasion. This is also known as "dragon syndrome." You end up not using them at all or using them so late they're more of a campaign afterthought.
Well, that's not going to happen with gelatinous cubes in my game anyway.
And just because, here are some stats for a killer 10 x 10 x 10 foot cube of carrion-eating jelly statted for GURPS 4th edition.
Killer Cube O' Gelatin
A 10 foot cube of hunting gelatin. "Attacks" by moving into/onto a target and then digesting it. Usually motors along at less than 1 yard/second, eating mold, fungus, carrion, and wood (including doors in a pinch!), but it can and will speed up if attacked or it senses a large amount of food.
ST: 0 HP: 10 Speed: 4.00
DX: 6 Will: 10 Move: 2
IQ: 1 Per: 8
HT: 10 FP: 10 SM: +4
Dodge: N/A Parry: N/A DR: 0
Slam or Touch (N/A): 1 point corrosive damage (every 5 pts damage reduces DR by 1 and inflicts 1 damage) (doesn’t affect most metals or any stone/pottery) plus paralysis (contact agent, resisted by HT-2), lasts 1 minute after no longer in contact with cube.
Envelopment (N/A): It can fully envelop paralyzed foes; envelopment does 10 points of corrosive damage per second, plus paralysis as above.
Traits: Amphibious; Discriminatory Smell; Doesn’t Breathe; Doesn’t Sleep; High Pain Threshold; Immunity to Metabolic Hazards; Immunity to Mind Control; Injury Tolerance (Homogenous; No Blood); Invertebrate; No Legs (Slithers); No Manipulators; Regeneration (1 HP/Hour, not from fire); Silence 3; Universal Digestion; Vibration Sense (Air).
Notes: Nonsentient and can’t negotiate. Plant/Slime spells won’t work. Gelatinous cube jelly is worth $10 a quart, 1d6 quarts can be gathered from a slain cube.
Editing Later: Check the comments if you want to see some suggestions for making this tougher. I didn't make it very tough, because I'm not sure why a scavenger should be a tough fight for even a slightly-prepared adventurer. This cube is a scavenger, meant for sweeping up the dungeon and making it perilous to leave the wounded behind, try to stash food, leave corpses you might want to zombie later, and so on. It's not a threat, although you can make it so if you prefer. I don't, so the version above isn't one. It's fodder at best. It's an obstacle, not an enemy, and it's really just a reminder that nothing that isn't alert and able to defend itself is safe in a megadungeon. It should be just as dangerous as a 10' pit - not at all if you're paying attention and ready, but potentially harmful if you aren't.