Teenage Mutant Ninja Turtles Teenage Mutant Ninja Turtles is a theme , officially first released in 2013 , although it was available in stores in some areas as early as December 2012 . It is based on the Nickelodeon TV show that premiered on September 29 th , 2012 in the US , which in turn is based on the Mirage comics by Kevin Eastman and Peter Laird . Seven more sets were released in 2014 , with three being based on the 2014 " Teenage Mutant Ninja Turtles " movie . Background . Season 1 . Ninjutsu master Hamato Yoshi ( Splinter ) is carrying his four pet turtles through the streets of New York City when he encounters members of an alien race called the Kraang . During an altercation with these aliens , Hamato and the turtles are exposed to their chemical , called Mutagen , and undergo major mutations . Hamato becomes a humanoid rat and the turtles become human / turtle hybrids . Splinter retreats to the New York City sewers , where he raises the four turtles as his sons and imparts to them his knowledge of ninjutsu . Now teenagers , the Turtles ( Leonardo , Donatello , Raphael and Michelangelo ) venture to the surface for the first time and learn that the Kraang is using the mutagen as part of their plan to take over New York City . The Turtles befriend the teenage April O ' Neil after she and her psychologist father Kirby are abducted by the Kraang . Donatello , who has developed a crush her , is able to save her , and while Kirby remains a prisoner of the Kraang , April becomes an ally of the Turtles as they help her to find out where the Kraang have taken her father . Meanwhile , upon learning of Splinter and the Turtle ' s presence in New York , Splinter ' s adoptive brother and long - time enemy , Oroku Saki ( Shredder ) , orders his Foot Clan to track down Splinter and his sons , and put an end to their clan . This family feud has the consequence of two of Shredder ' s deciples , world - famous martial arts star Chris Bradford and Brazilian street thug Xever Montes , getting mutated by Mutagen from one of the Kraang ' s Mutagen bombs into Dogpound ( later Rahzar ) and Fishface , and after Shredder learns of the Kraang ' s presence through his adopted daughter Karai , he has the Foot Clan enter an alliance with the aliens to destroy their mutual enemies in the Hamato Clan . The Turtles soon discover the Kraang and their leader , Kraang Prime , have come to Earth from Dimension X and built their headquarters within a company called TCRI to use the Mutagen and a set of psychic Kraang - like powers that April was born with to convert the Earth into a planet suitable for their race . After the Turtles finally rescue Kirby , the Kraang invade New York using their mothership , the Technodrome , but the Turtles and April emerge triumphantly as they send the Technadrome crashing into the sea . Sent by his sons to confront Shredder , Splinter learns that Karai is actually his own daughter , Miwa , who Shredder had kidnapped after his last battle with Splinter in Japan . depressed , he returns to the Turtles to celebrate their victory , promising to tell them the surprise he got from Shredder later . Season 2 . The Turtles struggle to contain an outbreak of mutations that occurs thanks to them accidentally spilling the leftover Mutagen from the thwarted Kraang invasion for the Kraang . Kirby becomes one of the victims in the outbreak , causing April to become very dissapointed and upset with the Turtles and break off her friendship with them . However , the Turtles earn her forgiveness when they save her from Karai , who has taken temporary command of the Foot Clan while Shredder is away in Japan . With April came her new friend Casey Jones , who helps Raphael repel a Foot Clan assault on the Turtle lair . Kirby is eventually restored to his human form when Donatello is able to construct another Kraang chemical , called Retro - Mutagen , and helps the other Turtles and April keep it away from former TCRI inventor Baxter Stockman , who was mutated into Stockman - Fly while employed by Shredder to make a perfect mutant army . Meanwhile , Shredder returns from Japan with mutated Japanese bounty hunter Tiger Claw as his new second - in - command . While helping Tiger Claw fight the Turtles , Karai is informed of her true past by Leonardo , who had a crush on her since Season 1 , but she is too reluctant to except it . When she is taken to the Turtle lair , she finally realizes the truth and disowns Shredder , who responds by imprisoning her . After the Turtles succeed in rescuing her , Shredder captures Karai again and uses her as bait for a trap that involves the Turtles mutating into snakes and unknowingly eating Splinter up . However , Karai ends up mutated instead , to everyone ' s horror . In response to this , Shredder makes a full alliance with the Kraang , who have finally perfected their Mutagen , and help them launch a second invasion on New York , starting with the destruction of the Turtle lair once the Kraang find it , forcing the Turtles to abandon it . The Kraang begin the city ' s entire population , including Kirby , despite Earth ' s military and the Turtle ' s efforts to stop them . Leonardo is gravely wounded after being ambushed by the Foot Clan , and Splinter is seemingly killed during a battle with Shredder . As a result , Turtles , April and Casey are forced to flee the city as the Kraang successfully conquer it . Season 3 . The group takes refuge at the O ' Neil family ' s summer home upstate in Northampton , New York in order to recuperate from their loss at the hands of the Kraang and the Foot Clan . Leonardo takes an extended amount of time to recover , but guided by an apparition of Splinter , is able to overcome his physical and mental wounds . The group eventually returns to the city with the goal of finding Splinter , Karai , Kirby , and their other missing allies , and liberate the city from the Kraang . They are successful in finding Splinter , and set up a temporary base in the abandoned Antonio ' s Pizza while Donatello works on perfecting his Retro - Mutagen for them to retro - mutate the Kraang - enslaved humans as the the search for Karai and Kirby continues . Meanwhile , Shredder mutates Russian arms dealer Ivan Steranko and his only known disciple , international master thief Anton Zeck , into Bebop and Rocksteady for stealing the Kuro Kabuto ( Shredder ' s legendary helmet ) and hunting Karai as a bargaining chip for the securing of their safe departure from the Kraang - taken city and assigns them to find her again . However , the duo withdraw from the mission to get revenge on the Turtles , who were also searching for Karai . This results with them unwittingly leading Bebop and Rocksteady to her so that they could recapture her behind their backs ( which they the duo successfully did ) and sneak her back to Shredder , who promises to cure her of her misery . The Turtles eventually re - take the city and retro - mutate everyone back with the help of a recently - formed mutant squad called the Mighty Mutanimals ( consisting of a few of the mutant friends the they met throughout the show , such as , Leatherhead , Pigeon Pete and Monkey Brains ) , but the effect of Foot Clan ' s involvement in the invasion has given Shredder power over the city ' s criminal underworld . This was done by earning control over many Asian gangs through the Purple Dragons ( under the leadership of martial arts gangster Hun ) , many South American gangs through Fishface , the Russian mafia through Rocksteady and the Sicilian mafia through Italian food critic Don Visiozo .