What is The worst Geronimo Stilton book?

As an educator with expertise in literature, it is important to recognize that opinions on books can vary widely among readers. However, some readers have criticized "The Karate Mouse" as one of the weaker entries in the Geronimo Stilton series due to its predictable plot and lack of character development. It is essential to remember that literary preferences are subjective, and what one reader may consider the worst book in a series, another reader may enjoy.