Simba, Timon, and Pumbaa's Adventures of Horton Hears a Who! is another upcoming Lion King/Ronald McDonald mixed crossover film planned to be made by Yakko Warner. It will appear on Google Drive in the near future.
A dust speck is dislodged from its obscure place and sent adrift through the Jungle of Nool. At the same time, Horton the elephant, the jungle's eccentric nature teacher, takes a dip in the pool. The dust speck floats past him in the air, and he hears a tiny yelp coming from it. Believing that an entire society of microscopic creatures are living on that speck, he places it atop of a clover. Horton finds out the speck harbors the city of Whoville and its inhabitants, the Whos, led by Mayor Ned McDodd.
He has a wife, Sally, 96 daughters (whose names all begin with the letter H), and one teenage son named JoJo. Despite being the oldest and next in line for the mayoral position, JoJo doesn't want to be the next mayor, and because he's so scared of disappointing his father, never talks. Once Horton begins carrying the speck with him, the city starts experiencing strange phenomena (earthquakes and changes in the weather), and the Mayor finds his attempts to caution Whoville challenged by the Town Council, led by the opportunistic yet condescending Chairman.
After he makes contact with Horton, the Mayor finds out from Dr. Mary Lou LaRue that Whoville will be destroyed if Horton does not find a "safer, more stable home". Horton resolves (with the help of his best friend Morton the mouse) to place the speck atop Mt. Nool, the safest place in the jungle. The head of the jungle, Jane Kangaroo, disbelieving Horton's beliefs and resenting him for overshadowing her authority, attempts several times to demand that Horton give up the speck, but Horton ignores her demands. Also taking force toward Horton are the Wickersham Brothers, a group of monkeys who love making misery. Eventually, the Kangaroo enlists a vulture named Vlad Vladikoff to get rid of the speck by force.
Vlad manages to steal the clover away from Horton and drops it into a massive field of identical pink clovers, causing an apocalyptic tremor in Whoville. After unsuccessfully picking nearly three million clovers, Horton eventually recovers the clover (exactly the 3,000,000th clover). The Kangaroo eventually finds out, thanks to Mrs. Quilligan, that Horton still has the speck, and decides to rally the jungle community into fighting Horton, saying that Horton's goal will lead to anarchy. Upon cornering him, the Kangaroo offers Horton an escape from punishment by renouncing Whoville's existence.
Despite Horton's heartfelt speech when he refuses, the Kangaroo orders the animals to rope and cage him, and to have the speck and the Whos destroyed in a pot of boiling beezlenut oil. The Mayor enlists all of his people to make noise by shouting "We are here!", as well as playing a variety of instruments, so the animals may hear them, assisted by JoJo's "Symphonophone", an invention which creates a huge musical contribution (which reveals that JoJo's "true" passion is music), but still fails to penetrate the surface of the speck.
As Horton lies beaten and captured, the Kangaroo easily takes the clover, and drops it. Meanwhile, JoJo grabs the horn used to project Horton's voice, runs up the highest tower and screams "YOPP!", breaking through the sound barrier just seconds before the speck hits the oil.
The Kangaroo's son, Rudy saves the clover from being destroyed and returns it to Horton. The animals finally hear the Whos and realize the truth and isolate the Kangaroo for tricking them. While being praised for his integrity by his neighbors, Horton even forgives the upset Kangaroo, and she befriends him with a makeshift umbrella for Whoville. Here, the people of Whoville and the animals of Nool gather in song and recite the chorus from "Can't Fight This Feeling". The film ends with the narrator revealing that the Jungle of Nool, or rather Earth, is just one speck, like Whoville, among numerous others, floating in outer space.
- King Julien, Maurice, Mort, Tarzan, Jane Porter, Professor Archimedes Q. Porter, Terk, Tantor, Louis, Genie, Sebastian, King Louie, Fu Dog, Rutt and Tuke, Roger Rabbit, the McDonaldland Adventure Crew, Yakko Warner's Pooh's Adventures team (excluding Winnie the Pooh characters), Ash Ketchum, Pikachu, Misty, Togepi, Brock, Littlefoot, Cera, Ducky, Petrie, Spike, Chomper, Ruby, Guido, Grandpa Longneck, Grandma Longneck, Skip, Mr. Thicknose, Kion and his friends, Homer Simpson, Marge Simpson, Bart Simpson, Lisa Simpson, Maggie Simpson, Santa's Little Helper, Snowball II, Grandpa Simpson, Patty and Selma, Milhouse VanHouten, Alex Whitney, Ned Flanders, Todd Flanders, Rod Flanders, Peter Griffin and his family, Glenn Quagmire, Joe Swanson, Cleveland Brown and his family, Tim the Bear, Stan Smith and his family, the Futurama gang, Bob Belcher and his family, Fred Flintstone, Wilma Flintstone, Barney Rubble, Betty Rubble, Dino, George Jetson, Jane Jetson, Judy Jetson, Elroy Jetson, Astro, Stan Marsh and his friends, Earl Sinclair and his family, Malcolm and his family, Artie, Pete, Eric, the Kids Next Door, Numbuh 362, Richie Cunningham and his friends (from Happy Days), Ralphie Parker and his friends, Dr. Alan Grant and his friends (from Jurassic Park), Jesse Katsopolis and his family (from Full House), Lou and his friends (from Cats & Dogs), Max and his friends (from The Secret Life of Pets), The Goonies, Jesse Greenwood, Elvis, Randolph Johnson, and Nadine guest star in this film.
- This film marks the first debut of The Smurfs as members of the McDonaldland Adventure Crew.
- This is an NTSC film with NTSC bits from The Lion King films, the Madagascar films, Tarzan, The Princess and the Frog, the Aladdin films, The Little Mermaid films, The Jungle Book, TaleSpin: Plunder and Lightning, Brother Bear 1 and 2, the Pokemon films, and The Land Before Time films.
- Madagascar: Escape 2 Africa and Horton Hears a Who! were released in 2008.
- Jonathan Oosterhof (aka LionKingRulezAgain1) originally planned to make a separate Lion King crossover with Horton Hears a Who!, but he retired from making anymore crossovers, so Yakko Warner will make this film as a Lion King/Ronald McDonald mixed crossover instead.
- Yru17 originally planned to re-edit a separate Land Before Time crossover with Horton Hears a Who!, but he retired from re-editing anymore crossovers, so Littlefoot and his friends ended up guest starring in this film instead.
- This film actually takes place after Littlefoot's Adventures of The Lion King (which explains Littlefoot and his friends already knowing Simba, Nala, Timon, and Pumbaa), the first two Land Before Time/Madagascar films (which explains Littlefoot and his friends already knowing King Julien, Maurice, Mort), Littlefoot Meets Tarzan (which explains Littlefoot and his friends already knowing Terk and Tantor), Littlefoot Meets The Princess and the Frog (which explains Littlefoot and his friends already knowing Louis), Littlefoot's Adventures of Aladdin, The Land Before Time/Little Mermaid trilogy (which explains Littlefoot and his friends already knowing Sebastian), Littlefoot's Adventures of The Jungle Book (which explains Littlefoot and his friends already knowing King Louie), Littlefoot's Adventures of Brother Bear (which explains Littlefoot and his friends already knowing Rutt and Tuke), and the first episode of Littlefoot's Adventures of American Dragon: Jake Long (which explains Littlefoot and his friends already knowing Fu Dog).