Twins Dipper and Mabel Pines visit their eccentric great-uncle for a summer in Gravity Falls, Oregon, where he operates the world's most bizarre museum. As soon as the twins arrive in Gravity Falls, they discover something amiss in the remote town.
Dipper and Mabel discover that 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.
In a quest to attain manliness, Dipper ventures into the forest to battle the notorious Multi-Bear. Meanwhile, Mabel tries to teach Grunkle Stan how to be attractive to women, particularly the waitress in the local diner, Lazy Susan.
After being challenged to a video game battle by 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.
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.
Li'l Gideon swindles the Mystery Shack away, forcing Grunkle Stan and the kids to move in with Soos. While Stan weighs how he can still care for his grandniece and nephew, they decide to take on Gideon.