Green slime

Green slime is a highly acidic type of semi-intelligent mold that can destroy flesh and other organic materials on contact. It clings to walls, floor, and ceilings, and is able to detect movement and drop onto prey below. It can also affect wood and metal, but not stone. A creature covered in green slime suffers ongoing effects until the slime is scraped off (which must be done immediately), or frozen or burnt. It is destroyed by sunlight.

On Golarion

A particularly massive colony of green slime exists on the floor of the cavern below the drow fortress of Harrowspire in the Darklands realm of Sekamina. The slime acts as a natural moat and an easy way for members of the Fighting Societies to dispose of captured intruders and failed trainees.