In three separate mysterious tales, Stan is cursed by a Witch, Waddles accidentally eats a bowl of brain-enhancing goop and builds a machine that allows him to speak for the first time, and Mabel faces her fear of Claymotion.
The episode begins with Stan welcoming a person (shown from first-person view in an attempt to make the viewer a character in the show) whose car broke down at night into the Mystery Shack, warning the person that he may be subject to "Tales Designed to Sell My Merchandise!"
Stan explains that after hours, the Mystery Shack has its spookiest attractions for sale. He offers the person a disembodied hand, which is ridiculously expensive. To support this, he tells a story called "Hands Off."
Stan steals a gold watch from a witch when he, Dipper and Mabel visit the local swap meet. The witch curses Stan, and he wakes up without hands the next morning. At breakfast, the twins discover this. Dipper recommend that Stan simply returns the watch, but he refuses. He asks Mabel to make him new hands, but when those work poorly, Dipper, Mabel and Stan visit the witch's secret hideout in a mountain cave, which they locate using a pamphlet from the swap meet. They find the cave to be filled with hundreds of disembodied hands, which attack them. The hand witch reveals herself. Stan returns the watch, but she claims the curse can only be broken by a kiss. At this point, Dipper proclaims that the witch is just making stuff up, and they discover that the whole thing was a ruse for the witch to get a date. Mabel suggests a home makeover, which the witch loves. She returns Stan's hands to him. After Stan and the twins leave, a mountain climber meets the witch and she flirts with him using a book Mabel gave her.
After the story, the person says they don't want the hand, which Stan tosses and it crawls away. So Stan offers to sell Waddles, calling him a magic pig.
Dipper receives a new puzzle toy, the "what-the-heck-ahedron." He finds it incredibly difficult, and Mabel suggest he might just not be smart enough to solve it. To prove her wrong, he locates the "percepshrooms" which journal 3 says will increase brainpower when ground up and smeared on the forehead overnight. Dipper does so, but soon after falling asleep, Waddles wakes up and eats the ground mushroom powder off of Dipper's forehead. The next morning, the twins wake up to see that Waddles has made a device that allows him to talk, and has solved Dipper's puzzle toy. While Dipper is amazed, Mabel soon learns that this is not the Waddles she used to have fun with, and becomes lonely. Dipper and Waddles work together to create inventions, eventually building the "Smarticle Accelerator," which will let Waddles solve all the mysteries of the universe. Mabel asks Waddles to remember all the fun they used to have. Waddles realizes that there is no point in helping the world if he can't help his favorite person in the world. He then activates the Smarticle Accelerator's reverse switch, reverting him to an ordinary pig, and causing the device to collapse. Dipper is devastated, but Mabel says a hug from Waddles will cheer him up. Dipper hugs Waddles, and the pig regurgitates the What-the-Heck-A-Hedron, which Dipper finds gross.
Back in the Shack, the person refuses Waddles as well. Stan replies by offering some spooky VHS movies.
Dipper, Mabel, Stan, and Soos are watching a movie called "Believe in Yourself," which only Mabel likes. Stan puts in "The Voyages of Loinclothiclese." To Mabel's dismay, the film has claymation, which Mabel has a childhood fear of. She goes and hides in a laundry basket until Stan decides to take everyone to the house of the film's director, Harry Claymore, to prove claymation is harmless. Claymore's house is somewhat old, and Stan, Dipper, Mabel and Soos soon discover that it is inhabited by a giant clay cyclops and clay skeletons. They find Claymore tied up, and he explains that he used black magic to make the clay figures animate themselves. However, when computer animation was invented, the figures were out of a job, so they went crazy and turned on him. Claymore says that the clay monsters will turn them into clay monsters too by covering them in clay. Mabel, having run off, wonders what to do. While fiddling with loose clay, she has an idea. She remolds the cyclops into Shimmery Twinkleheart, a character from Believe in Yourself, which crushes the other clay figures while Mabel frees her friends. They are glad Mabel conquered her fear, but she explains that she's twice a scared now, but now it's a rational fear. Back at the Shack, the gang watches another Loinclothiclese movie, and Stan says he's glad no one was turned into clay. However, they discover that Soos is now made of clay, and Stan throws the VCR at his head to get rid of him.
After that story, when the person still refuses to buy anything, Stan offers them a free sample of a potion. When they drink it, they pass out. They later wake up trapped in a glass box, now a Mystery Shack attraction dubbed "The Cheapskate." During the end credits they play tic-tac-toe with Mabel, who keeps bending the rules.
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- Additional Written Material by:
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- Additional Voices:
- Tyler is shown running a stand titled "Sev'ral Chimes," a reference to the boy band Sev'ral Timez from "Boyz Crazy."
- The agents return from "Scary-oke," Powers appearing at the Gravity Falls Swap Meet and Trigger in the bowling alley.
- Dipper is shown reading journal 3 under black light to reveal its invisible ink, which was first revealed in "Scary-oke."
- Waddles carries a Jack-o'-melon trick or treat bucket from "Summerween."
- There is a musical montage of Waddles "remembering" his time spent with Mabel, which includes a scene from "The Time Traveler's Pig."
- Several of Mabel's sweaters make a reappearance.
- The wavy sweater she wore in the "The Time Traveler's Pig" during Waddles' flashback.
- Mabel's shooting star sweater as seen in the opening and "Tourist Trapped."
- Sprinkles sweater first seen in "Soos and the Real Girl."
- Music note sweater first seen in "The Inconveniencing."
- Blue stars sweater first seen in "Boyz Crazy."
- A sweater resembling the lightning bolt one she wore in Double Dipper, although this one is red, while the other was black.
- Another sweater resembling the golf course one she wore in The Golf War, although this one is red, while the other was green.
- The claymation segments during Clay Day were animated by Stoopid Buddy Stoodios, Inc., best known for providing the animation to the TV series Robot Chicken.
- Before telling the story "Hands Off", Stan tells the traveler that the object they are holding is not for sale and warns them to keep their hands off, before taking the object from the traveler. The object seems to be a Palantír from The Lord of the Rings, showing the Eye of Sauron.
- When the witch constructs the throne of hands in "Hands Off", it somewhat resembles the Iron Throne from Game of Thrones
- During the ending credits, there is a cryptogram that reads "PVREK BIG QF. JCDQZRF’ ZNVEFH OBCX: "C BEWRS VVUTBFL BT BKNX CVAY BKNX CVAY BKNX"" Using the vigenère cipher, it translates to "CHECK OUT DR. WADDLES’ LATEST BOOK: "A BRIEF HISTORY OF OINK OINK OINK OINK OINK"."
- The page section at the end of the episode says, "23-12-12 23-10-15-11-23-4-15-9-10 on the top left, and "15-5 22-12-23-21-13 11-23-17-15-21" on the bottom right, which translates to "ALL ANIMATION and "IS BLACK MAGIC" after being put through the combined cipher.
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