Teenage Mutant Ninja Turtles (2003)

S07E02 Karate Schooled

The Turtles join forces once again with Casey and April, only to discover that Casey has fallen under the influence of his charismatic new martial arts teacher. As they delve deeper, they realize he’s been manipulated and turned against them through intense brainwashing techniques. Now, the Turtles must devise a plan to break the mind control and bring their friend back to his true self before it's too late.