I think that's why Dreamworks got Weird Al on to the movie. I mean, they are going all out to make the movie like a fusion between the first four books (The original with the first act, Attack Of The Talking Toilets with the Turbo Toilet 2000 and his Toilet Minions playing a pivital part of the film, the 3rd one with the excessively long title of from what the music video showed us with Captain Underpants already getting superpowers plus the kids are seemingly turned zombie-like, and The Perilous Plot Of Professor Poopy Pants with Professor Poopypants playing the main antagonist do the film and the sizenator gun he uses is a fusion between his growth and shrinking machine), so why not go all the way?