Gelatinous Cubes

Gelatinous Cubes are a monster from the Dungeons & Dragons multiverse that are known to plague adventurers by trying to devour them whenever encountered, they often have the remains of previous victims within their forms and are may even have enchanted weaponry stick inside their acidic forms, as can be expected the arrival of a Gelatinous Cube is dangerous despite any potential rewards it may bring if defeated and it is often the most common Ooze that players will encounter in most campaigns, especially those involving traditional dungeon-style exploration.

History
Gelatinous Cubes are a type of Ooze that often inhabit dungeons, where they take advantage of their alien physiology to form living walls by which unwary victims may become absorbed - at which point the Gelatinous Cube will dissolve them slowly from within via powerful acidic slime, leaving little but bones, weapons and armor inside its large form. Motivated by instinct Gelatinous Cubes seek only to spread, feed and hunt - a trait they share with almost all Oozes.

Appearance
Gelatinous Cubes come in a variety of colors but are known for having a shape that is roughly that of a large cube - they often utilize this cube-shape to their advantage when hunting in narrow corridors or hallways, their oozing body often has skeletal remains of victims inside as well as armor or weapons, any organic material (save for bones) have long-since been dissolved by the creatures acidic slime.

Abilities
Gelatinous Cubes are known for their ability to absorb victims into their cube-like bodies, which proceed to dissolve a victim with powerful acid - if not rescued in time a victim becomes little more than a skeleton, effectively being digested over time by the ooze.

Trivia

 * the Gelatinous Cube is by far the most iconic of all fantasy monsters created by D&D, rivalled only by the Beholder, the Gelatinous Cube has thus been found in almost any media imaginable in many different forms, despite its simplistic form and mentality.
 * while D&D has innumerable types of Ooze monsters the Gelatinous Cube remains the most popular, like all Ooze in the D&D multiverse they are subservient to Juiblex.