When Dipper and Mabel hear rumors of a sea monster that lives at the bottom of the local lake, they enlist Soos to take them on a boating expedition to prove it really does exist.

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.

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.

The twins discover a hidden room inside the Mystery Shack and compete over who should have it.

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 Waddles is snatched by a prehistoric beast, Dipper, Mabel, Stan, Soos, and Old Man McGucket must journey to a mysterious land trapped in time to rescue him.

The Pines family is starting to get everything back to normal after the Lil' Gideon incident. They throw a “Mystery Shack Is Back” party, but some unwelcome guests intend to crash it.