Does anyone know the title of a movie where....?

A boy is being chased through a sewer and falls into a world ruled by kangaroo looking people?! I recall the title being two words. Sorry this is so vague my boyfriend confided in me that he used to love this movie when he was younger and I want to rent it for him. He also mentioned something about the 'roo people being represented by the different elements or something? Or that they were like ninjas? The more I try to describe this the more I think it's made up.