Teenage Mutant Ninja Turtles: The Mega Mutation

Plot
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 Braain. During an altercation with these aliens, Hamato and the turtles are exposed to an alien chemical called mutagen and they undergo major physical transformations. Hamato Yoshi becomes a humanoid rat and the turtles become anthropomorphic turtles. 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 venture to the surface for the first time and learn that the Braain is using the mutagen as part of their plan to take over New York City. The Turtles befriend the teenage orphan Casey Jones and the teenage student April O'Neil after she was abducted by the Purple Dragons.