Ben 10 The Aipom

A boy named Billy is transformed into a cat due to an angry magician who decides to teach the boy a lesson after seeing him bullying a cat. In order to keep his family from worrying, the magician also uses his magic to make his cat, Dandelion, assume Billy's own form and live with his family. No matter how much he begged during the series, Billy was never turned back into the boy he used to be.