Twins Dipper and Mabel Pines visit their eccentric uncle for a summer in Gravity Falls, Oregon, where he operates the world's most bizarre museum. In the opener, the twins arrive in Gravity Falls and soon discover something amiss in the remote town.
Dipper and Mabel hear rumors that a sea monster lives at the bottom of the local lake, they enlist Soos to take them on a boating expedition to prove it really does exist.
When someone tampers with Mabel's life-size wax statue, she and Dipper set out to find the culprit. Meanwhile, Grunkle Stan mourns over the loss of his wax doppelganger.
Dipper and Mabel discover their seemingly cherubic new neighbor, Lil' Gideon, happens to be the town's adored psychic. But when Lil' Gideon guilts her into dating him, she and Dipper soon learn that his cuteness can fade all too quickly.
Dipper is invited by teens on a trek that leads to an abandoned convenience store that may be haunted.
Dipper tries to prove his manliness by battling a notorious bear; Mabel tries to teach Grunkle Stan how to be attractive to women.
When Stan throws a big weekend party to promote the Mystery Shack, Dipper uses an off-kilter copy machine to make clones of himself so he can impress Wendy. Meanwhile, Mabel stands up for her two friends and fights for the Party Queen title in their honor, instead of having the popular girl and her group win.
When Dipper and Mabel discover evidence that the reported town founder is a hoax, they set out to expose the historical cover-up and prove that Mabel's silliness is not a bad thing. When Gravity Fall's holiday, Pioneer Day, comes around, Pacifica Northwest makes an announcement about her great grandfather, Nathaniel Northwest. Pacifica makes Mabel feel bad by telling her she's silly, and Mabel decides she should be more serious. Dipper then finds an article in his 3 book that says Nathaniel Northwest was a fraud. Enclosed was a map, with the triangle symbol. Dipper thinks they should burn the document, until Mabel makes a hat out of the paper, which shows them a map to Gravity Fall's Museum of History. There's an abstract painting shaped in a triangle, and when Mabel turns upside down, it reveals an angel, and she comments that she saw that statue in the cemetery. Once at the cemetery, Mabel sees the statue, and she pretends that the statue is picking her nose. She bends the statue's finger, opening a secret passageway. Mabel and Dipper enter it, revealing many Top secret documents. They come across a document called the Northwest cover-up, and the true founder of Gravity Falls was Quentin Trembley.
Dipper wants to correct a mistake he made in the past with assistance from a time machine. Meanwhile, Mabel is overjoyed when she wins a pet pig at a fair.
After being challenged to a video game battle by Wendy's boyfriend Robbie, Dipper is shocked when his favorite playable fighter, Rumble McSkirmish, comes to life to defend him, but Dipper soon loses control over Rumble McSkirmish and has to find a way to stop him.
Dipper gets unconformable with the fact that he is shorter than Mabel. So he searches for some magic that can make him grow. Meanwhile, Lil' Gideon plans to tamper with siblings' heights.
Dipper and Mabel go trick-or-treating in the summer and encounter a candy-loving monster who threatens to devour them if they don't bring him sweet things to eat.
Mabel and Stan make a bet that whoever makes the most money in three days can run the Shack for the summer.
While Stan, Dipper, Mabel and Soos are falling in a bottomless pit, they tell stories to pass the time.
Mabel befriends a cute merman who gets trapped in the deep end of a public swimming pool. Meanwhile, Dipper volunteers at the pool so he can work alongside of Wendy.
Dipper and Mabel compete to win a hidden room in the Mystery Shack, but the contest gets tricky when it's discovered that the room's carpet has body-swapping properties.
When Mabel discovers that her favorite boy band is actually a bunch of imprisoned clones, she sets them free, only to decide on keeping them for herself. Meanwhile, Dipper is convinced that Robbie plans to brainwash Wendy with a secret message hidden inside one of his songs.
When a prehistoric beast snatches Waddles; Dipper, Mabel, Stan, Soos, and Old Man McGucket must journey to a mysterious land trapped in time to rescue him.
Dipper, Mabel and Soos must travel through Grunkle Stan's mind to defeat a tricky dream demon summoned by Lil Gideon.
Pint-sized huckster Li'l Gideon has swindled the Mystery Shack away, forcing Dipper, Mabel and Grunkle Stan to move in with dimwitted Soos and his grandmother. When Stan weighs whether he can still take care of his grandniece and grandnephew, Mabel and Dipper decide to take on Gideon.