Books like captain underpants and the big, bad battle of the bionic booger boy

Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy are the sixth and seventh books in the Captain Underpants series by Dav Pilkey. The first part was published on August 1, 2003, and the second part was published on September 30, 2003. The duology features the debut of George and Harold's new pets Sulu (a hamster with a bionic endoskeleton) and Crackers (a Quetzalcoatlus) who first appeared in the first and second parts respectively. The second part also features the debut of time travel in the series, which would become a core theme of the series later on. The full color covers will be for Part 1's color called Purple and Blue. but Part 2's color called, Yellow and White.