Slinking their way through cold swamps and bleary marshlands, or sometimes even dungeons and caverns, gray oozes consume any organic materials they encounter. Despite its lack of intelligence, the gray ooze is a most problematic creature due to its transparency. While the ooze cannot easily climb walls or swim, its habit of lurking in the thick mud that lines the banks of marsh pools or lying in harmless-looking pools on dull-colored dungeon floors makes it dangerously easy to overlook and step on.

Some sages believe that the gray ooze is the result of a failed alchemical experiment, while others postulate that the first gray oozes spontaneously arose from a cesspit of magical detritus. Of course, these theories that gray oozes are not living organisms, but rather the alchemical result of an unfortunate mixture of rare caustic fluids and magical waste, are derided by many who dwell in areas plagued by the creatures but which do not have a long history of magical pollution.

The gray ooze adapts readily and swiftly to changes in environments, the simple structure of its primeval form and its method of using fission to reproduce all but ensuring that such changes occur. Listed below are two such variants that adventurers have encountered.

Id Ooze (CR 6): Perhaps the strangest variant gray oozes are those that have developed a rudimentary intelligence, including the ability to communicate telepathically with other oozes, or even the ability to blast enemies with pulses of raw mental power. Id oozes are advanced gray oozes with an Intelligence score of 2 (and thus gain skill ranks and feats—typically 4 ranks in Stealth, Improved Initiative, and Toughness), can communicate basic empathic information with other id oozes within 100 feet via telepathy, and can use lesser confusion at will as a spell-like ability (CL equals the id ooze's HD).