Captain Underpants:The Preposterous Plight of the Purple Potty People by Dav Pil

Captain Underpants, George, and Harold got cloned. They wanted to prank everyone but the George and Harold stopped the pranks. The bad Captain Underpants and the good Captain Underpants had a war. The good Captain Underpants, George, and Harold won the war by defeating the bad clones of themselves