Mustakozene-80 was a gaseous chemical. It produced severe mutations on contact with the skin. It was also known to excite the Morlox creatures.
Professor Megelen conducted a series of unethical experiments on Morloxes using Mustakozene-80, attempting to fuse together two forms of tissue into one. After being exposed by the Third Doctor, he continued his experiments and his usage of the chemical caused him to mutate into a half Karfelon/half Morlox being. (TV: Timelash)