[[WMG: What we saw at the end of Book 9 was just a prank.]]
[[spoiler:George and Harold may be giant zombie nerds now, but they're still pranksters at heart. The "red squishy stain" left behind was actually some ketchup covering Tippy.]]
* It appears I was partially right: [[spoiler:ketchup was indeed involved, but George and Harold's personalities had nothing to do with Tippy's survival]].

[[WMG: There's still one Tippy Tinkletrousers left.]]
As of the end of ''Captain Underpants and the Revolting Revenge of the Radioactive Robo-Boxers'', there were four Tippies in existence -- the original Tippy (who may or may not have escaped from jail by now, depending on whether he was still tasked to build the Warden Gordon Bordon Shmorden statue), Tiny Tippy/Supa Mega Tippy (who was created during Tippy's original trip to George and Harold's Kindergarten days), Big Tippy (who was created when Tippy went back to fix the timeline), and Slightly Younger Tiny Tippy (who was created when Tiny Tippy was sent to see where George and Harold disappeared to). The three Tippies created through time travel died during the events of the book, leaving the original Tippy (who was simply not involved with the story) still at large.
* Actually, the original Tippy was Big Tippy. He went back to when George and Harold were in Kindergarten by accident, then went forward, which caused the apocalyptic scene, then he went back to when George and Harold were in Kindergarten to prevent that from happening, and that's what caused the first two Tippys. So yeah, they're all dead.

[[WMG: Every villain that's not dead will return.]]
So Tippy Tinkletrousers has returned, but [[spoiler: died at the end of Book 10]], and both the ending and the teaser stated that the next book will have a return of [[spoiler: Melvin Sneedly and the Turbo-Toilet 2000]]. Every villain who isn't dead might return for another book until the very last book, which might feature a return of Dr. Diaper.

[[WMG: Post your film adaptation ideas here.]]
George and Harold essentially ruined everyone's good day in the first book, so to give them a AdaptationalHeroism , they did the prank as a retaliation to the [[JerkJock Jerk Jocks]] and the AlphaBitch cheerleaders. To have Mr. Krupp KickTheDog, the boys actually finished to do the chores unlike in the book but Mr. Krupp decides to release the video out of spite.