Littlefoot's Adventures of Scooby-Doo! The Mystery Begins is the first Land Before Time/Scooby-Doo crossover film planned to be re-edited by yru17. It is planned to be shown on either YouTube or Vimeo after Littlefoot's Adventures of Pokémon 3: The Movie.
Littlefoot and his friends (along with Stan, Kyle, Cartman, Kenny, and Genie) time-travel to Coolsville and meet four teenagers named Shaggy, Fred, Daphne, and Velma and a dog named Scooby-Doo. When the school is taken over by three ghosts, Littlefoot, Cera, Ducky, Petrie, Spike, Chomper, Ruby, Guido, Stan, Kyle, Cartman, Kenny, Genie, Scooby-Doo, Shaggy, Fred, Daphne, and Velma must team up to solve their first mystery.
- Stan Marsh, Kyle Broflovski, Eric Cartman, Kenny McCormick, and Genie guest star in this film.
- This is an NTSC film with NTSC bits from The Land Before Time series, South Park: Bigger, Longer & Uncut, and the Aladdin trilogy.
- Ash Ketchum, Pikachu, Misty, Brock, Togepi, Team Rocket (Jessie, James, and Meowth) were originally supposed to guest star in this film, but yru17 found out that Disneydaniel93 will start making Pokémon/Scooby-Doo crossover films starting with Ash's Adventures of Scooby-Doo on Zombie Island, so he decided to cut them out of this film.
- SpongeBob SquarePants, Patrick Star, Squidward Tentacles, Sandy Cheeks, Eugene Krabs, and Sheldon J. Plankton were originally also supposed to guest star in this film as well, but yru17 found out that RatiganRules is already planning the guest star SpongeBob and Patrick in his Winx Club/Scooby-Doo movies starting with Bloom's Adventures of Scooby-Doo on Zombie Island (due to skb2108 requestng RatiganRules to guest star them in his films), so he decided to cut them out of this film as well and ended up replacing them with Genie from Aladdin, which now means that there are no guest villains working for the three ghosts in this film.