If you’re a GM, the gelatinous cube either works for you, or it doesn’t. But as far as I’m concerned, the cube is one of the classics. (Evil wizards have to keep the dungeon clean somehow.)
A local brewer is also a bootlegger, running the whiskeys he distills to escape the taxes the crown takes out of his beer. His basement features two trapdoors: one that leads to a cavern lined with bottles, and another that leads to a gelatinous cube (that is also the tavern’s garbage disposal).
The Velvet Cosh was a thieves’ guild shut down a year ago. When a party unearths one of their safe houses, they find a number of traps that no longer function due to lack of maintenance—needle traps whose poison dried out, floor triggers that have rusted solid, and the shriveled lozenge of what was once a gelatinous cube. After cleaning out the guild’s storerooms, they discover the very same gelatinous cube now quite active. The cube was only in torpor, resuscitating itself after encountering the stimulus of fresh prey.
After teleporting blind into a dungeon, a young wizard fell prey to first a glyph blast, then a gelatinous cube. The agony of his death brought the wizard back as a ghost, and in undeath his agony continues—rather than being tied to his corpse, the wizard’s spirit is anchored to the constantly roaming cube that digested him. Freeing his amulet from the cube’s nucleus could free the ghost, but he is too pain-wracked to communicate this and attacks anyone not paralyzed by the cube.
—Dungeon Denizens Revisited 21 & Pathfinder Bestiary 138
Rob McCreary (yet again) is the sage to consult on gelatinous cubes in Dungeon Denizens Revisited.
Also, this Cracked article is dead wrong about the gelatinous cube (and the ash rat, the atropal, and the grell). It’s got the roving mauler pegged, though. That thing was stupid.