Grey oozes were sluggish subterranean predators that resembled wet stone or slick gray rock, usually spreading around 8 inches thick and up to twelve feet long. They formed thick puddles of sludge that blended easily into cave floors, striking at prey that strayed too close, though had no real intelligence. They could perceive the area around them through a sixth sense, but lacked eyes to see past the radius of their blindsight; as a result, they typically were found in subterranean areas, as they required no light to see.
The ooze's acid dissolved metal, and their transparent bodies made them difficult to see until they attacked. They were immune to most magic, as well as heat, acid, and cold, making them a difficult opponent to fight as they battered prey until it fell, then engulfed it to digest the remains. They reproduced by budding after feeding, and dragged themselves through caverns, dungeons, and sewers in search of anything they could consume. When they grew large, grey oozes sometimes developed a dim intelligence or latent psionic ability, a trait thought to have emerged from living near Illithids.
Due to their ability to dissolve metals, some Artificers and blacksmiths kept small samples of the ooze for use in shaping metal.