Mutagen, also known as Retromutagen Ooze, is a mucilaginous substance that has served as a key plot device in nearly every medium of the Teenage Mutant Ninja Turtles. Any creature that is exposed to mutagen will rapidly increase in size, strength and intelligence (sometimes), and even gain superpowers. It is responsible for mutating, among others, Splinter, the four turtles, and villains such as Alopex, Bebop, Rocksteady, among others.