At some point in his life, Stan Pines used a military-grade grappling hook in a heist. Details of the heist are unknown, but he kept it afterwards. He later left it in a box in the Mystery Shack and forgot about it.
At the end of "Tourist Trapped," Stan said that the twins could each choose one item from the Mystery Shack gift shop, but forgot the grappling hook was there. Consequently, Mabel chose it as her gift and, despite Stan's initial protests, was allowed to keep it. She is later seen "shutting off the light" with it, and ends up breaking both the window and lamp in the process.
Much later, in "Gideon Rises," Mabel says she is going to defeat Gideon Gleeful and take back the Mystery Shack with the help of her grappling hook. When they plan on sneaking in and taking the Shack's deed, Mabel fires it. It hits a tree branch, which then falls on Dipper. Dipper asks if she'll finally admit that the hook is useless and Mabel says "Nope!" Later, after Dipper defeats Gideon and his Gideon-bot falls off a bridge, Mabel uses the grappling hook to save herself and her brother.
In "Scary-oke," Mabel holds the grappling hook while sleeping in her bed.
In "Not What He Seems," Mabel uses her grappling hook as a zipline in order for her and Dipper to infiltrate the Mystery Shack after it has been secured by the government agents.
In "Weirdmageddon 3: Take Back The Falls," after the Resistance breaks into the Fearamid, Mabel uses it to grapple up to the top of Bill's Throne. She finds Ford, and throws the grappling hook down to Dipper, who joins her. Later, she uses it to help her and Dipper escape from Bill. In the episode's credits, Stan grabs Ford and uses the grappling hook to carry them both up and out of the screen.
Mabel's hook looks like an ordinary grappling hook with the actual hook at the front, and the rope tied to the side. It is completely black, while the hook is silver in color.
Her grappling hook, like any other, consists of four main parts: the claws (or "pokey bits" as she calls them), barrel ("super-tuber"), trigger ("maker-goer") and retractable cable ("ropey part").
- 201. "Scary-oke"
- 211. "Not What He Seems"
- 219. "Weirdmageddon 2: Escape From Reality"
- 220. "Weirdmageddon 3: Take Back The Falls"
- According to Alex Hirsch, after the events of "Gideon Rises," where Mabel used the grappling hook to save herself and Dipper, she keeps it with her at all times. If Mabel is on screen and the grappling hook can't be seen, it's because she's hiding it in her sweater.