Rex the Runt (1998)

Rex arrives home to find that there's a mouse in the kitchen. But this is no ordinary mouse, he is preternaturally strong, extremely aggressive and refuses to be kicked out. The Gang even resort to getting Tiddles the Cat round to sort him out. Then the mouse reveals that he was once Rex's pet mouse, Morris, who Rex sold to Dr Dogg for animal experimentation. A tearful reunion ensues.