Captain Underpants

Captain Underpants is a series of books written and illustrated by Dav Pilkey and published in 12 volumes by Scholastic from 1997 to 2018. Two boys, George Beard and Harold Hutchins, hypnotize their principal, Mr. Krupp, into thinking he's a superhero called Captain Underpants, but then they make the mistake of pouring water on his head to bring him back to normal. This results in him slipping back and forth between trance and reality whenever he hears the sound of fingers snapping.

The Adventures of Captain Underpants (B01)
In the (in-universe) comic book, the students throw away their "Stinky Taco Surprise", which then comes to life as the Inedible Hunk and eats everything in sight, eating the gym teacher off-page.

Captain Underpants and the Attack of the Talking Toilets (B02)
In the (in-universe) comic book, a spaceship shoots a beam at the school that brings the toilets to life. They get hungry, and (much to the students' delight) one eats the gym teacher. Captain Underpants arrives and sticks plungers into the toilets' mouths, causing them to get stuck. The Turbo-Toilet 2000 comes out of the spaceship, but Captain Underpants wedgies him and shoots him into the spaceship, whereupon they both explode, resulting in the toilets returning to normal.

Within the actual story, George and Harold, who have been serving detention for ruining the Invention Convention (from which they were banned for a stunt they pulled at the Invention Convention the previous year) attempt to use Melvin's Photo-Atomic Trans-Somgobulating Yectofantriplutoniczanziptomiser 2000 (called PATSY for short) to make copies of their comic, but instead accidentally bring the Talking Toilets (but oddly enough, no one else from the comic) to life. The boys run away, but are caught and suspended by Mr. Krupp, who refuses to listen to their warning about talking toilets. The teachers decide to throw a party in the gym to celebrate, ignoring the boys' warnings. Mr. Meaner mockingly opens a door repeatedly, but is then swallowed by a Talking Toilet, prompting the other teachers to run away. Ms. Ribble, Mr. Krupp, George, and Harold stay frozen in fear, until Ms. Ribble snaps her fingers at the toilets and (futilely) tells them to go away. Now turned back into Captain Underpants, Mr. Krupp runs out of the school to grab underwear. George and Harold follow him (whilst being chased by a Talking Toilet). Upon returning, the trio finds the school destroyed. Ms. Ribble runs, chased by the Talking Toilets, who have swallowed all the other teachers. Captain Underpants promises not to let them eat her up, but then one does. After an unsuccessful attempt to subdue the Toilets with underwear, George, Harold, and Captain Underpants run into the school cafeteria to get something disgusting and come across creamed chipped beef (which was to be tomorrow's lunch). They immediately proceed to feed the lunch to the toilets, causing the toilets to regurgitate everything (and everyone) they ate and fall down dead. Just as the boys remember that the machine copied everything on the front cover, the Turbo-Toilet 2000 comes running out of the school. Captain Underpants tries to fight him, but because he (currently) has no superpowers and is merely an overweight man hypnotized into thinking he is a superhero, the Turbo-Toilet 2000 soon defeats and swallows him. At their wits' end, George and Harold run into the school, draw a character called the Robo-Plunger, and use the PATSY 2000 to bring it to life. The Robo-Plunger defeats the Turbo-Toilet 2000, and George and Harold pull out Mr. Krupp (who has turned back to normal as toilet water has gotten on his head). Following a deal with them, Mr. Krupp cancels the boys' suspension and detention, and watches as the Robo-Plunger fixes the school, grabs all the Toilets, and then flies to Uranus.

Captain Underpants and the Invasion of the Incredibly Naughty Cafeteria Ladies from Outer Space (and the Subsequent Assault of the Equally Evil Lunchroom Zombie Nerds) (B03)
After a prank by George and Harold causes the lunch ladies to quit, three evil aliens, Zorx, Klax, and Jennifer disguise themselves as lunch ladies to feed the school Evil Zombie Nerd Milkshakes and turn them all into zombie nerds. George empties the carton of Super Evil Rapid-Growth Juice out a window, but does not notice the contents falling on a dandelion, which grows into a giant monster and later tries to eat Captain Underpants when the trio is jumping out of the spaceship (just before it explodes). George gives Captain Underpants some Extra-Strength Super Power Juice, allowing the hero to defeat the Dandelion of Doom.

Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy, Part 1: The Night of the Nasty Nostril Nuggets (B06)
After he snitches on them for a toilet prank and lands them in detention, George and Harold make a comic making fun of Melvin. The comic shows Melvin as a tattletale who becomes mayor after telling on a guy who has robbed a bank. Melvin quickly goes on a power trip and starts making new rules, resulting in people being arrested left and right. Soon, all of the jails are full, prompting Melvin to create the Tattle-Tron 2000, which functions like a robot eating people. Captain Underpants arrives and (not wanting to hurt the people inside) feeds the robot prune juice, and (in an analog to how prune juice works) all of the prisoners come out through a pipe. Captain Underpants then defeats Melvin and sends him to jail. In revenge, Melvin tries to use his Combine-O-Tron 2000 to combine himself with a robot, but (due to allergies from his family's cat, Danderella) he sneezes at the last second. He eventually gets acclimated to his new form, but when cold and flu season arrives, he starts sneezing more frequently. Mr. Krupp announces a field trip to the Snoddy Bros. Tissue Factory, which greatly horrifies Melvin. Mr. Snoddy, the plant manager, shows everyone tissues, horrifying Melvin even further. Oblivious to Melvin's anger, Mr. Snoddy keeps throwing tissues at Melvin, turning him into a monster. He grabs Ms. Anthrope, prompting Mr. Krupp to run away. Fortunately, George snaps his fingers and turns Mr. Krupp into Captain Underpants, whereupon the hero saves Ms. Anthrope. Unfortunately, Ms. Anthrope (accidentally) turns him back into Mr. Krupp by kissing all over his face, and Melvin grabs him. George and Harold frantically start snapping their fingers, but because of the kiss juice, the snaps have no effect, and Melvin swallows Mr. Krupp. Melvin then grabs George and Harold and tries to swallow them too, but Melvin's hamster, Sulu (who had earlier been combined with a robot by the Combine-O-Tron 2000) hears their cries. He saves the boys, and then uses some novelty items to defeat Melvin. Melvin's parents arrive, and (under George's suggestion) Melvin's father switches the batteries of the Combine-O-Tron 2000 to get his son back to normal, blasting the body into three chunks of boogers. However, the blast morphs Mr. Krupp and Melvin together, and although another blast separates them, it also switches their brains. Just then, one of the chunks smashes the Combine-O-Tron 2000, and the three boogers all come to life and start to chase the gang.

Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy, Part 2: The Revenge of the Ridiculous Robo-Boogers (B07)
The three Robo-Boogers (named Carl, Trixie, and Frankenbooger) are still chasing our heroes at the beginning of the book, but Sulu suddenly grabs the boogers in his mouth and then spits them into outer space. The boys eventually get another Combine-O-Tron 2000 (via time travel) and use it to switch Melvin and Mr. Krupp back to their own bodies. As it turns out, however, Captain Underpants' powers have gone to Melvin, who is unwilling to do anything until George and Harold change an embarrassing comic they made of him. Meanwhile, Carl, Trixie, and Frankenbooger have hitched a ride back to Earth and are eating the control tower at the local airport. George, Harold, and Captain Underpants distract the boogers and are chased to a shopping center, where they throw various things at the Robo-Boogers. Upon eating an orange that Captain Underpants throws at him, Carl disintegrates from the Vitamin C stored in his meal. George and Harold start throwing oranges at Trixie and Frankenbooger, but the two, having gotten wise to the power of Vitamin C, dodge all of their ammo and then grab the boys in an attempt to eat them. Fortunately, Captain Underpants arrives and distracts them with the Underpants Dance. Greatly annoyed, Trixie and Frankenbooger grab the seat of a novelty toilet (which Captain Underpants is standing on) to hoist themselves onto the roof, only to crush two crates of oranges that spray juice on them, killing them.

Captain Underpants and the Tyrannical Retaliation of the Turbo-Toilet 2000 (B11)
A ball shot by a robotic version of Harold in Book 5 goes hurdling to Uranus and hits the Robo-Plunger on the head, decapitating it and causing juice to go pouring into the mouth of the Turbo-Toilet 2000. Revived, the robot disassembles the Robo-Plunger into a rocket scooter and flies back to Earth for revenge. On Earth, he begins a rampage in Piqua, causing a very annoyed Melvin to yell at him to be quiet. Angered, the Turbo-Toilet 2000 chases after Melvin to the school, where Melvin hides under Mr. Krupp's desk. He finds a toenail and throws it away, but then realizes that it might contain Mr. Krupp's DNA. He goes looking for it, but is soon found by the Turbo-Toilet 2000. Melvin manages to escape and inserts the toenail into his watch, which has a DNA extractor. Upon reaching his bedroom laboratory, he converts the toenail's DNA to a concoction and drinks it just before the Turbo-Toilet pops him into his mouth, only to find it hard to swallow him. He pulls out Melvin, who then uses his new powers to completely slay him. Melvin is declared a hero (and dubbed "Big Melvin") and enjoys the perks at first, but when people start abusing his help for menial tasks, he finally resorts to tracking down George, Harold, and Mr. Krupp to return them to the present from the Cretaceous period. He dresses in a Robo-Squid, goes to the past, and brings back the whole group. Because they didn't go to school, however, George and Harold are in trouble with their parents and forced to do several chores. This greatly exhausts them, but their luck worsens when they remember that the next day is Test Day. They try to study, but succeed only in exhausting themselves even further, resulting in them sleeping through the school day. The situation worsens the next day when they discover that it was not just Test Day they slept through, but Super Secret Test Day. Not only are the boys not allowed to take makeup tests, but final exams have also been canceled, meaning that the boys have no homework, quizzes, studying, or means of bringing their grades back up. Their final grades are calculated, and while George will move to the fifth grade, Harold has to be held back. Fortunately, George remembers the Robo-Squid, and the boys go back in time to finally take their tests. Unfortunately, they end up creating duplicates of themselves. They take turns during the week, with one duo going to school and the other hanging out at the treehouse. When they start to run low on supplies, George and Harold sneak into school to print a comic they made, only to be seen by Ms. Anthrope. They quickly convince her that she is dreaming when their doubles show up, and she strips into her underwear and goes running around. This process goes on with more of the school staff, except for Mr. Krupp, who instead reacts with utter shock. Eventually, the police arrive and arrest everyone, except Mr. Krupp, who is sent to a mental institute due to his mental collapse. The Turbo-Toilet 2000 (who, in this timeline, was not killed by Melvin) arrives twelve days later and causes havoc in Piqua. After an unsuccessful attempt to convince the nurse to let them see Mr. Krupp, the boys disguise themselves as Talking Toilets and lure the Turbo-Toilet 2000 to the institute. George quickly snaps his fingers into a microphone, snapping Mr. Krupp out of his comatose state and turning him into Captain Underpants. He takes on the Turbo-Toilet 2000, and because he has actual superpowers this time, he is able to hurt the monster. Unfortunately, the Turbo-Toilet 2000 starts crying, and one of his teardrops lands on Captain Underpants's head, turning him back into Mr. Krupp. The Turbo-Toilet 2000 chases and captures him, but upon learning that the monster wants two annoying kids, Mr. Krupp leads the Turbo-Toilet 2000 to the treehouse of George and Harold. Yesterday George and Yesterday Harold hear the vibrations and try to hide. Mr. Krupp asks to be let go, but instead, the Turbo-Toilet 2000 swallows him and rams into the treehouse. Fortunately, this causes some eggs lain by Crackers (a pterodactyl George and Harold found in Book 7) to hatch, releasing some half-hamster, half-pterodactyl hybrids she had with Sulu. While the boys are pondering what they are, the Turbo-Toilet 2000 grabs them, only to then be grabbed in turn by the creatures. They lift him into the sky and then drop him, whereupon he smashes into pieces, freeing Mr. Krupp.