Codename: Kids Next Door S04 E22 Operation: F.E.R.A.L.

Numbuh 1 is sent to retrieve an important code from Rainbow Monkey Island, but after a run-in with the Delightful Children From Down the Lane, he is left stranded there. Soon, he ends up forgetting who he is and starts behaving like a wild Rainbow Monkey. His teammates become very worried when it appears that there may be no way to cure him.