When Ethan's grandma suggests they take a zip line to school, Ethan realizes that his grandma is a little different. In fact, she's a ninja! Ethan is soon the hit of the school when his grandma drops from the ceiling at show-and-tell, and teaches the kids karate moves and how to do backflips in slow motion. But when his grandma deflates his team's soccer ball, everyone is upset--including Ethan. Why can't he just have a regular grandma? But when Ethan...