On Christmas with a trip to Korea, Darlyn Paguio invited Kai Smith (who he hates Christmas) to come with her. However, Kai is shown risking going "Frederator" - a term coined when one of the Frederator Studies, Finn the Human from Adventure Times, a 2010 Cartoon Network show, which resulted in show being canceled after eight years. Kai is depressed that he has remained orphaned since his his parents left. Misinterpreting this as stress from overwork, Darlyn has her father books a korea so they can all celebrating the holiday and spend more time together as a family.
Unfortunately, a demons outbreak has occurred, which leads to Darlyn, Kai and Kai’s sister, Nya fighting off hordes of evils on the way to rescue Jones. When she arrives, she discovers Jones is kidnapped by a black haired girl with strange magic who turned him into a lego version of Jones. They manages rescue him, only to hatch a Feast, a dangerous monster from the movie called Feast. Lego Jones and the Feast monster stumble into an escape pod, which is launched out of the game, and crash land in Land of Dimedale-Ooo, a crossover world between Adtuver time and Fairly Odd Parents. With Jones missing, one of the elves, Cooper Blossom, upon learning from his brother, Danny that Jones has left his game, ventures to Korea and allies with Ninjago oc heroines, Kate Ross and Jade Lee, to retrieve Darlyn and the others.
A little boy, Jimmy Neutron and his rebel gang, Manolo Sanchez, Flint Lockwood, Z Marion, Manny Rivera, Miguel Rivera and Rodney CopperBottom, steals lego figure, mistaking Jones for this to buy their way into the nightly race that determines which characters are playable the next day, but King Stan, the ruler of Land of Dimedale-Ooo, forbids their follower, Timmy Turner from joining Jimmy from racing because Jimmy has glitches that cause her to teleport erratically. Meanwhile, Jones escaped with the antidote, ventures to rich manor owned by one of Stan’s followers, Miguel and Tuilo, the girls, Margo, Edith and Agnes as he ended up doing some chores but was able to escape, heading to help his friends and they agree to work together to retrieve his cure to turned him back to human form and help Jimmy win hand of Timmy.
They build a kart and hide out at San Angelville, an city, where Kai, Copper (who come here at the same time) and Jones teaches Jimmy to do Spinjizu. They spending their time togather in their trip.
King Stan’s Prime minister, Finn hacks the show’s code to obtain antidote medal, and offers it to Jones in exchange for preventing Jimmy from hoping Timmy. He claims that if Jimmy wins and be with Timmy, his glitches will lead to Land of Dimedale-Ooo being cancelled; unable to leave the show because of his glitch, Vanellope will be left to die while King Stan, Finn and their subjects become homeless in the arcade. Jones reluctantly agrees and destroys Jimmy’s kart. Heartbroken, he declares Jones "really is a last bad guy in universe" and runs off distraught. Upon leaving the Korea, which he was finally reverse to his human form next morning, Jones notices Jimmy and Timmy image on the show poster, Jimmy Timmy Pour Hour and realizes Jimmy and Timmy‘s crossover was meant to be a real.
Meanwhile, after Cooper left, Danny, Jay, Jade and Kate search for Darlyn, the others and Kai, but she abandons them when Jay inadvertently reminds her of her husband, first born child daughter, younger son and baby daughter and son who were murdered and eaten by a Feast monster on their Christmas day. Jay is later imprisoned in King Stan's castle, but Jones frees him and Darlyn along with Kai and Nya, and where, Jimmy explains Timmy’s abduction and brainwash by the Frederator 20 years ago. Jimmmy blames himself for Timmy being chosen, and regrets that he hadn't been able to save him. Sensei Wu discovers a swarm of Feast monsters underground, which hatch and start devouring the show.
Jimmy participates in the race, but is attacked by Finn. Jimmy’s glitch reveals he is actually cult of Frederator, who took over Fairly Odd Parants and displaced Jimmy to replacing with crossover called Finn Timmy Power Hour. Jimmy do Spinjizu to escape Finn, who is then eaten by a Feast. Darlyn and the others evacuate the show, but Jimmy is trapped due to his glitches. When Cooper points out that the Feast monsters can be attracted and destroyed by a beacon of light as in movie, Jones decides to make Mountain erupt, replicating the beacon with Kai. They are confronted by Frederator, now fused with the monster that devoured him. Jones makes the mountain erupt and falls into its depths to sacrifice himself, allowing Kai to escape using Airjitzu. The volcanic beacon lures and permanently destroys the Feast and Frederator.
After finding Jones was safety, Kai has Cooper to find him but he was gone and Jimmy and Timmy, now be togather forever. Kai learns that he finally faces his fears and decided to made up Darlyn for himself.