Dipper & Mabel's Adventures of Scooby Doo: The Mystery Begins is the first Gravity Falls/Scooby Doo crossover to be created by 12Adventureboy/12Adventureboy2. It is unknown when it will be made.
Dipper, Mabel, Soos, Mushu, Lazlo, Raj, Clam, Chowder, Grunkle Stan, Randy Cunningham/Ninja, Howard Weinerman, Mac, Bloo, Kick Buttowski, Gunther Magnuson, the Eds (whom are hanging out with Dipper & Mabel), and the Mane 6 (whom Dipper, Mabel, and the team have met for the first time), go 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, Dipper, Mabel, their Adventure team, The Eds, Mane 6, Scooby-Doo, Shaggy, Fred, Daphne, and Velma must team up to solve their first mystery.
- Ed, Edd, n Eddy, Twilight Sparkle, Pinkie Pie, Rarity, Applejack, Rainbow Dash, Fluttershy, and Lil' Gideon will guest star in this film.
- This film takes place after Dipper & Mabel's Adventures of Ed Edd n Eddy: The Big Picture Show since Dipper & Mabel already know the Eds. And this also takes place after Justin Roman's Twilight Sparkle's Adventures of Ed Edd n Eddy: The Big Picture Show since they also know the Eds and are part of the Eds' Adventure Team.
- The Mane 6 will meet Dipper, Mabel, and their team for the first time. Mabel, Pinkie Pie, Soos and Ed will form a strong bond with each other, Twilight and Double D will be rather interested in Dipper's number 3 book, Kick, Bloo, Rainbow, and Eddy will form a good friendship due to them wanting to be cooler than the other.
- This is The Mane 6's first guest star appearance in a Dipper & Mabel adventure film.