Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy

Part 1: The Night of the Nasty Nostril Nuggets

At demonstration speech day, George and Harold shows off the "Squishy"; two ketchup packets under a toilet seat. But Melvin forces everyone to watch his demonstration, the "Combine-o-Tron 2000", which he uses his hamster Sulu and a robotic hamster body he built to show off. Melvin orders Sulu to do some tricks for the class, but the hamster's able to spank Melvin himself. After noticing the scene, George and Harold adopt Sulu, who happily joins the two. Meanwhile, Ms. Ribble uses a Squishy on an already grumpy Mr. Krupp, who believes that George and Harold are responsible. When Mr. Krupp finds them in the lunchroom, Melvin almost immediately tattles on the boys and Mr. Krupp sends them to detention, causing them to make a libelous Captain Underpants comic starring Melvin.

Having read the comic, Melvin angrily goes home and builds a super-powered robot. However, Melvin sneezes at the last second from an allergy and gets combined with the robot and boogers, turning him into the Bionic Booger Boy. Eventually, he even acquires his own drinking fountain. Cold and flu season begins, however and when the class visits a tissue factory, owner Snoddy offers free tissues, but Melvin becomes gigantic as a natural defense. George turns Mr. Krupp into Captain Underpants and the man saves his secretary, Miss Edith Anthrope. Her wet kisses turn him back and Melvin devours him, but Sulu defeats Melvin using large size novelty items from warehouses.

George's suggestion, reversing the batteries in the Combine-o-Tron, surprisingly works, and only three robotic booger globs fly off. However, Mr. Krupp and Melvin's brains have accidentally switched bodies and the globs come to life and smashes the Combine-o-Tron.

Part 2: The Revenge of the Ridiculous Robo Boogers

The robo-boogers chase the heroes to a dead end, but where Sulu spits them out into outer space. After a number of incidents, George and Harold discover the body mix up. Since it'd take "Mr. Melvin" six months to build another machine, George suggests going back in time, which makes Melvin snap his fingers. George and Harold are forced to tell the secret and "Mr. Melvin" orders them to create a comic about him, before setting to build. The next day, "Mr. Melvin" is furious that the former mentioned depicts him as uncool, but soon explains to them if the machine's used two days in a row. He also gives them the "Forgetchamacallit 2000", against one's short term memory. George and Harold decide two days back.

However, the boys end up in the Cretaceous period and get a Quetzalcoatlus, who they nickname "Crackers". The two go to when Singerbrains is driving to the police station. George convinces her she is dreaming because of "the dinosaur's presence", etc. Harold sends Crackers back, then they erase her memory and travel to the present. Meanwhile, "Kruppy the Kid" is helping two old ladies cross the street. He successfully rescues a cat from a tree at the same time, but accidentally leaves the ladies up there. They, and other victims of him, including Anthrope, form an angry mob. "Mr. Melvin" finds Underpants and switchs one another back.

In space, the boogers land on a spaceship, hanging on as it returns to Earth, before they start destroying the space center. Underpants goes off to help, but discovers that his powers were taken by "Big Melvin", who refuses to help unless George and Harold changes the comic. Captain Underpants and the boys are cornered at a local store and starts throwing random items stacked outside. By chance, Carl is killed upon swallowing an orange. The other boogers become cautious, but Captain Underpants makes an deliberatily annoying "Underpants Dance", making them climb up his chosen building, right into a well-placed orange-made Squishy.

Soon, "Big Melvin" lies to the Eyewitness News crew while George and Harold sneak back to school, returning with the machines. Captain Underpants gets his powers back, then the crew and audience's memories are erased. When the boys return to their clubhouse, Harold is keeping Crackers as another pet, which George allows for a night. The next day, however, they end up in an opposite fictional universe...

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