This creature looks like a quivering puddle of water.
Crystal Ooze CR 4
A crystal ooze strikes by slamming into its opponents. Paralyzed victims are devoured.
The digestive acid that covers a crystal ooze dissolves metals and organic material, but not stone. Each slam and constrict attack deals 1d6 additional acid damage. Armor or clothing worn by a creature grappled by a crystal ooze takes the same amount of acid damage unless the wearer succeeds on a DC 20 Reflex saving throw. A wooden or metal weapon that strikes a crystal ooze takes 1d6 acid damage unless the weapon’s wielder succeeds on a DC 20 Reflex save. The ooze’s touch deals 12 points of acid damage per round to wooden or metal objects, but the ooze must remain in contact with the material for 1 full round in order to deal this damage. The save DCs are Constitution-based.
Due to its lack of vivid coloration, a crystal ooze is difficult to discern from its surroundings in most environments. A DC 15 Perception check is required to notice the ooze. Any creature that fails to notice a crystal ooze and walks into it automatically suffers damage as if struck by the ooze’s slam attack and is immediately subject to a grab attempt by the ooze.
Environment any aquatic
The crystal ooze is an aquatic variety of the gray ooze. It is semitransparent and clear and almost impossible to see in the water. The crystal ooze can grow to a length of up to 8 feet and a thickness of about 6 inches.
Crystal Ooze from the Tome of Horrors Complete, Copyright 2011, Necromancer Games, Inc., published and distributed by Frog God Games; Author Scott Greene, based on original material by Gary Gygax.