Mutagen creates the turtles’ mutations in Teenage Mutant Ninja Turtles II: The Secret of the Ooze.
The 1991 sequel expands the franchise’s origin mythology by revealing more about the substance that transformed the turtles and Splinter. In the film, the characters investigate TGRI, a company connected to the mutagen and to the origins of the transformed animals.
The movie uses the word “ooze” prominently in its title, but mutagen is the more specific name for the mutation-causing substance. The film also introduces Tokka and Rahzar, two mutant creatures created through exposure to the same material.
This terminology can vary across continuities. Some versions emphasize “the Ooze,” while comics, cartoons, and films may use terms such as mutagen or mutagenic ooze. The underlying idea remains a chemical or alien substance that causes biological transformation in the franchise’s fictional universe.