Grey oozes are subterranean creatures that closely resemble wet stone or slick rock. Fluid and fast, they reside in low places, such as on dungeon floors, and strike, serpent-like, at those who come near. They are highly mobile oozes, and actively hunt, though being unable to climb surfaces limits their range. They have no real limit to their upper size, but they tend to grow like a puddle, spreading out over a long area, remaining quite thin.
Grey oozes can sense creatures nearby, and eagerly lash out, serpentine, hoping to feed its ever-hungry colony. Grey oozes dissolve metal very rapidly, eating through armor and weapons as it attacks. Its acids don't harm stone or wood, but it does dissolve flesh very quickly.
Grey oozes are immune to most magic, as well as to fire and cold damage, but they are vulnerable to lightning.
Some grey oozes develop rudimentary psionic abilities, unleashing psychic crush on creatures that display similar sensitivity.
Metallurgists of great skill use small grey oozes in stone jars to etch ans score metalwork. It is dangerous work, as the little oozes can lash out at their keepers, making this kind of work very rare.
1e Monster Manual
2e Monstrous Manual
3e Monster Manual