During an altercation with these aliens, Yoshi and the turtles are exposed to a mysterious radioactive alien chemical substance ooze called Mutagen which causes organic beings to undergo major physical transformations.
Yoshi becomes (and takes of the characteristics of) a humanoid brown rat and the turtles become anthropomorphic, they take on human characteristics.
After a five year run spanning five seasons and 124 episodes, the show concluded on November 12, 2017 and will be succeeded by a new 2D animated reboot series (which was revealed under the title Rise of the Teenage Mutant Ninja Turtles), set to replace this series on Nickelodeon in September of 2018.
It's the turtles' fifteenth birthday and they're itching to venture up to the surface and showcase their ninja skills. At first, they love the surface with its weird lights and even stranger food (like pizza).
Merchandise based on the series includes a new line of Teenage Mutant Ninja Turtles consumer products and six LEGO sets.Season 3 was released on October 3, 2014 (one week after the Season 2 finale) and concluded on September 27, 2015.Season 4 aired on October 25, 2015 and concluded on February 26, 2017, both seasons contained 26 episodes per season.Nickelodeon acquired the global rights to Teenage Mutant Ninja Turtles from the Mirage Group and 4Kids Entertainment, Inc.and announced a new CGI-animated TMNT television series.