As it rains, Dipper and Mabel play a game in the attic to pass the time. Then Stan calls them downstairs to make fun of Gideon's latest commercial. The gang proceed to recall their past experiences and their mutual dislike of him, and soon after they hear Gideon break in and attempt to unlock Stan's safe. They confront Gideon, who initially does not take Stan seriously, but ultimately flees when Stan hits him with a broom and chases him out with it. Stan checks on the deed while Gideon plots to release a secret weapon to get into Stan's mind.
Later, as Wendy and the Pines are watching a western movie, Mabel suggests they switch the movie to Dream Boy High, which the others refuse to watch. Terrified by a bat in the kitchen, Soos rushes into the living room, and Stan sends a reluctant Dipper to take care of the problem; Dipper ends up injured after the encounter. Afterwards, Mabel and Soos tend to his injuries while Dipper complains about always having to do the hardest chores. Soos replies that Stan's personality is one of "life's great mysteries," and Soos decides to investigate another such mystery: whether or not it is possible to lick one's own elbow. Stan shortly after calls Dipper to fix the clogged sink, which angers his nephew even more.
Meanwhile, Gideon performs a ritual to summon the dream demon Bill Cipher, who engages in various antics before making a deal with Gideon: he will invade Stan's mind, and Gideon is to help Bill with an unknown favor later. Mabel and Soos, who witnessed the entire occurrence while hiding behind a bush, rush back to the Shack to tell Dipper, who was in the process of sweeping while his uncle slept, what they saw. Dipper consults Journal 3 and reads of the dangers of Bill, and watches the demon descend upon Stan's mind. After learning that they can prevent Bill's chaos by traveling into Stan's head themselves, they prepare and recite the necessary incantation.
Inside Stan's mindscape, the gang explore a bit and meet Bill, who is expecting them. Mabel tries to tackle him but instead goes into and right back out of the mysterious creature, who expresses issues a warning and his extreme doubt, because of his power. Mabel remains skeptical that he can figure out what she is thinking of, but is overjoyed when he brings her boy fantasy to life, and Bill shoots Dipper with a laser before entering the Shack in Stan's head in search of his sought out memory. After a bit of goofing around, the gang ventures into the psychological Shack to search through Stan's memories, which include time in Colombian jail, being a door-to-door vacuum salesman, his disastrous date with Lazy Susan, and more. While Dipper sneaks a peek at Stan's memories of him to find Stan's apparently disappointing, true feelings about him, the others--including Bill disguised as Soos--look for and find the proper door.
Bill reveals his true form, teases Mabel and Soos, and runs off with the memory, and when Dipper arrives shortly after, he express rage about Stan hating him. Dipper refuses to offer further help, and the others go to confront Bill without him. As Bill is about to give Gideon the code, Mabel shoots the memory of the code out off Bill's hand and into the bottomless pit. This sends Bill into a fit of extreme anger, in which he establishes an arena to face Mabel, Soos, and Mabel's dream boys with his weapon of choice: nightmares. Meanwhile, as Dipper searches for an exit, he comes across the memory of Stan expressing his actual feelings toward Dipper, and after watching the rest of the memory, learns that Stan is only hard on him to prepare him to face the world. However, he is sucked into the memory, and the Stan within the recollection informs Dipper of the ability to do whatever he wants within the mind.
Dipper then realizes that he must stop Bill and rushes off. As the demon is torturing Mabel and Soos with their nightmares (a British dog man for Soos, and making Mabel ugly) and prepares to finish them off once and for all, Dipper arrives with the news of being able to make dreams reality and demonstrates the ability to his comrades via laser vision. Mabel decides to give herself the ability to shoot kitten heads from her arms, Soos utilizes a question mark beam from his stomach, and so forth. Just as Soos, the twins, and Mabel's dream boys are about to send Bill out of Stan's head, he stops them, warns them of an approaching evil, and leaves. Stan wakes up and thereby forces Soos and the twins out of his head. They are relieved to have been rid of Bill, but their relief is cut short as Gideon reveals that he used dynamite to obtain the deed to the Shack, which gives him ownership according to Gravity Falls' odd laws, and forces the "trespassers" out as he has Bud destroy the building. The credits convey the message of "to be continued."
- Written by:
- Directed by:
- Storyboards by:
- Matt Braly
- David Gemmill
- With the Voice Talents of:
- Additional Voices:
- Stan knows how to box.
- Stan hides his arrest warrants under the carpet in the Gift Shop.
- Stan was "the biggest wimp" on his school playground when he was younger.
- Stan had freckles as a child.
- Stan had braces when he was a teenager.
- One of Mabel's nightmares is losing her cuteness.
- Soos has nightmares of a British dog man.
- Mabel mentions her date with Gideon, referencing "The Hand That Rocks the Mabel."
- The "Explosion/Muffin" that Robbie spray painted on the water tower appears again.
- Memories of Stan include clips from "The Inconveniencing," "Double Dipper," "Irrational Treasure," "The Time Traveler's Pig," "The Legend of the Gobblewonker," "Boss Mabel," "Bottomless Pit!," and "Land Before Swine."
- The 80's style boys from Mabel's fantasy in "The Legend of the Gobblewonker." become actual characters.
- Mabel's dream of having a human sized hamster ball from "The Legend of the Gobblewonker." is practically realized.
- The cloning copy machine appears in Stan's office again.
- We glimpse a scene of Stan's time in a Colombian prison as mentioned in "The Hand That Rocks the Mabel."
- We get a glimpse of Stan's date with Lazy Susan that was mentioned in "Dipper vs. Manliness."
- We see the beginning of Stan's relationship with Carla McCorkle.
- Stan's secret behind the vending machine is addressed for the first time since "Tourist Trapped."
- Bill knows "lots of things." related to famous conspiracies. Among those that flashed across his body was Nathanial Northwest's statue, the cave room where The Northwest Cover-up was located in, Stan entering the entrance behind the vending machine, the broken arm of Gideon-bot from "Gideon Rises," and the Gravity Falls State Prison.
- Also a closeup of the stamp from the opening sequence's title card.
- When Gideon goes to the page for summoning Bill Cipher, the -$12 Dollar Bill reappears again after being first shown in "Irrational Treasure."
- Viewership: This episode was watched by 2.7 million viewers on its premiere night.
- In an earlier version, Bill made his appearance to Dipper in a dream.
- In Gideon's commercial, the Lil Gideon in Lil' Gideon's Tent o' Telepathy has an MT after it instead of TM, the symbol for "trademark."
- Before going into the kitchen to fight the bat, Dipper picks up a saucepan and a spoon, both of which are nicknames of the constellation the Big Dipper.
- The spell Gideon used to summon Bill is "Triangulum, entangulum. Veneforis dominus ventium. Veneforis venetisarium." Which roughly translated in Latin is "Triangle — I invoke you. I come to the defensive barrier of the mind. I will see the barrier destroyed."
- Dipper chants the following to allow them to enter Stan's mind: . . . . . . . . . Taken together, the incantation is nonsensical. See individual sentence translation by hovering your mouse over the phrase.
- When Gideon falls to his knees and his eyes glow blue he shouts something intelligible. When played backwards you can hear he's actually saying, "Backwards message! Backwards message! Backwards message! Backwards message! Backwards message!"
- While remembering Stan, Bill flashes an image that matches Stan's tattoo.
- On Bill's page in Journal 3 the words "ATBASH," "CAESAR," and "A1Z26" are crossed off. These are the names of the ciphers used throughout the show.
- Bill refers to Dipper, Mabel, and Soos as 'the pine tree', 'the shooting star', and 'the question mark', which are symbols surrounding his image on his page in Journal 2.
- The number 618 appears multiple times throughout the episode.
- In Stan's mindscape, the moon looks like his magic 8-ball cane.
- In the memory of Stan as a child and getting bullied in the playground, just before he is hit in the face with a soccer ball, a sports team name "Jersey Vultures" is seen behind him.
- The first view of Stan's memories where it shows many memories at an angle, the scenes show his fez without the yellow symbol.
- Two monster versions of Stan's head appear in his dreamscape. One is a bat-form, which has the current fez symbol. The other is a younger-looking version (no prominent ears) with crab legs, with no fez symbol.
- Stan's mindspace version of the Mystery Shack has "PBVWHUB VKDFN" over the main entrance, which is a Caesar cipher for "MYSTERY SHACK."
- In front of Stan's mindscape version on the Mystery Shack is a Pitt Cola machine that has "SLWW" written on it, which is a Caesar cipher for "PITT."
- The top of the dreamscape Shack has a broken off sign that says "OAUVG." Once decoded it reads "MYSTE." However, instead of the usual three letters used in most of the show's caesar cipher, it is decoded using only two letters back.
- In one shot of the hallways in the mindscape Mystery Shack in the production art, "EWTUG AQW OCTKNAP" is carved into a wall. Decoding it using two letters back translates to "CURSE YOU MARILYN."However, in the actual episode, this message is edited out.
- During the end credits of this episode, there is a cryptogram that reads "20-15 2-5 3-15-14-20-9-14-21-5-4..." Once decoded, it reads "TO BE CONTINUED..."
- The original cryptogram was supposed to be "NEXT WEEK: XYLER AND CRAZ'S BODEXCELLENT RADVENTURE."
- In yellow behind Bill Cipher's name is a message that reads, "Template:LTemplate:ITemplate:ATemplate:RTemplate:SpaceTemplate:MTemplate:O-Template:N-Template:S-Template:T-Template:ETemplate:RTemplate:SpaceTemplate:S-Template:N-Template:ATemplate:PTemplate:PTemplate:YTemplate:SpaceTemplate:DTemplate:RTemplate:ETemplate:S-Template:S-Template:ETemplate:R." Once decoded, it reads, "LIAR MONSTER SNAPPY DRESSER."
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