Bill Cipher is a triangular dream demon existent only in the mindscape with unknown motives. He has been running amok in Gravity Falls, Oregon since being summoned by Stanford Pines.
Info
Personality
Bill is an eccentric, insane he is also crazy (according to Gideon), possibly psychopathic, and physically irreverent demon who finds most things amusing (although no one is really sure why). He's outrageous and outlandish, as well as a quick talker and thinker. Though he may come across as simply annoying, he's not to be taken lightly; when angered, he's a force to be reckoned with.
When possessing Dipper's body, Bill is shown to be rather masochistic, hurting himself in various ways for the thrill of it, finding pain "hilarious." He seems to have little knowledge about the human body—specifically its physical limits.
Appearance
Bill is a yellow, triangular creature that bears a strong resemblance to an Egyptian Pyramid and the Eye of Providence. He has a single large eye rimmed with four short black lashes on its top and bottom. He moves around mostly by floating about, and rarely actually stands on his own two feet. He has thin, black limbs, wears a small, black bow tie, and has a tall, thin, black top hat that floats just above his head. His arms do not seem to be in any fixed position, and can be moved along his perimeter without any difficulty. He has also been seen carrying a small, black cane which turned yellow in Season 2.
Summoning Ritual
To summon Bill Cipher, one needs a picture of their victim. The eyes must be crossed out and the picture must be surrounded by eight candles in a circular formation. Then the following incantation must be recited: "Triangulum, entangulum. meteforis dominus ventium. meteforis venetisarium!" Your eyes will glow blue. The sky will turn grey as you enter the mindscape. You'll say "backwards message" backwards 5 times (Asetnoheptus Asetnoheptus Asetnoheptus Asetnoheptus Asetnoheptus). A triangle appears. One eye opens and it turns into Bill's normal appearance. However, it is shown that Bill has the ability to temporarily pull other beings into his plane of existence, if he so pleases, as seen in "Sock Opera."
Preventing Bill's Chaos
In order to prevent Bill's chaos inside someone's mind, one must light nine candles and place their hand on the victim's forehead. Say the following incantation: Fidentus omnium. Magister mentium. Magnesium ad hominem.Magnum opus. Habeas corpus. Inceptus Nolanus overratus. Magister mentium. Magister mentium. Magister mentium. If spoken the reciter of the incantation's eyes will turn blue and will be brought to the victim's mind on how they picture, where they have to find a way to stop Bill themselves.
There are also three known preemptive methods to stop Bill from entering minds. The first known method is a shielding spell that involves moonstones, mercury, and unicorn hair. The second method is placing a physical barrier around the mind, such as Ford's metal plate, though Ford stated it's not the safest method. The last method is "encrypting" a subjects thoughts, making it too difficult for Bill to read. It is safer than the second method and more mobile than the first, but very time consuming.
Abilities
Bill's abilities are focused around the mind and mental manipulation. He's described as a "dream demon" and displays some of the characteristics of a demon including creating contracts with his summoner. When he is summoned, he appears to put everyone and anyone observing into a trance-like dream. The effect is that the world seems to turn colorless, and he can effect the surrounding environment however he likes, as demonstrated by pulling out and returning a deer's teeth. The people observing are unaware they've fallen asleep until Bill leaves and then they realize their eyes have been closed during his whole meeting. Bill can enter people's minds through their dreams. Once inside a mind he can manipulate anything, including his shape and form and changing the landscape. He can communicate with his summoner like a video call, using his body as a window. In fact he can use his whole body as projector and display images. His body also seems to lead to a pocket space and runs in a slightly different time. (e.g., Mabel jumps into Bill's body and several seconds pass before she reappears, none the wiser.)
Once inside of a mind he can also easily pluck information from any others who are also inside and bring those ideas and images to life. The conjured images seem to take a life of their own such as the case with Xyler and Craz.
Bill is also at least close to omniscient. He knows "lots of things," including the truth of many well known conspiracies as well as future events, such as the destruction of Gideon-bot and that Gideon Gleeful would go to prison.
Bill also has the ability to remove people's souls from their bodies, and take possession of the body afterwards. The person who is removed from their body is stuck in a ghost like form in the mindscape, unable to affect the rest of the world, unless they find a vessel. This vessel doesn't have to be a living thing, as Dipper, who was a victim of this, used Mabel's sock puppets to warn her.
Bill is also known for having godlike abilities, such as being able to see things from the eyes of any image of himself. This explains why through out the show he is pictured in almost every episode.
The Cipher Files
Stanford Pines has a file containing information on Bill Cipher and various sighting of him throughout history. The file contains pictures and a page ripped out of a book, with images of a pyramid (presumably in Egypt) and the Eye of Providence. Another page in the file is titled "Alligans Contractus" (which is latin for "Binding Contract" with a picture of an old man shaking Bill's hand, both of which are surrounded by a blue flame, signifying the man is making a deal. There is also a trifold paper with three titled: Our World (with a drawing of a human head), Mindscape (with a drawing of a person and Bill and the coded message: Black and White), and Nightmare Realm
Story in Gravity Falls
While not being able to solve any of the mysteries of Gravity Falls, Ford became desperate. He stumbled across a cave that contained an inscription regarding something all-knowing. Even when told not to summon, Ford recited the incantation out loud, but nothing happened. Later that day, Ford went to sleep in the woods and come across Bill in his dreams. Bill claimed to be a muse who chose one great mind to inspire every hundred years, and told Ford that he had chosen him. To Ford, Bill seemed to be a very friendly guy. They made a deal: for the rest of Ford's life Bill could possess him whenever he wanted to, and in return Bill gave him plans to make a portal to unlock many more mysteries of Gravity Falls. While Ford was testing the portal, Fiddleford McGucket accidently went into the portal and saw what Bill was actually planning behind Ford's back. Ford then decided to shut down the portal to prevent Bill's plan, and ever since, Bill has been waiting for the portal to reactivate.
Bill and the symbol he's based on, the Eye of Providence, appear frequently in Gravity Falls. He was the unseen creator of the cryptograms in the online game Rumble's Revenge.
Season 1
A picture of Bill is shown briefly at the end of the opening theme. A similar picture is seen in the entry about him in Journal 2. Encircling him are various symbols that link to various characters in the show. Most notably, when he appears physically for the first time, he refers to Dipper, Mabel, and Soos, as "Pine Tree, Shooting Star, and Question Mark" respectively. The entry also makes special note of the glasses symbol, the author of the book seemingly having been alarmed by this. Underneath "Name: ???" is the text: "This odd, triangular being has appeared in my dreams every night for weeks."
His full name appears in his entry in Journal 3. Behind his name is a message encrypted with a symbol substitution cipher; when decoded it reads: "Liar Monster. Snappy Dresser."There are various notes scattered about the page, such as "Is he watching me?" and "Bill has proven himself to be one of the friendliest and most trustworthy individuals that I've ever encountered in my life. What a guy! I honestly can't trust him more. Not evil in any way, Bill is a true gentleman." However, the latter note is crossed out and below another note reading "Can't Be Trusted!" can be found written in red ink. On the next page, a diagram of a human head and various aspects of its mind is shown, its top being opened up for a drawing of Bill to enter it. In the lower right corner of the page "DO NOT SUMMON AT ALL COSTS!" is written in large, red letters. The rest of the page is spattered with a dark red substance.
"Dreamscaperers" is the first time Bill is directly addressed and introduced in the series. Gideon Gleeful, in an attempt to take over the Mystery Shack once again, summons him. Gideon tells him to steal Stan's safe combination directly from his head, so that Gideon can steal the Shack's deed. Bill agrees once he knows it's Stan, but in return Gideon would have to help him in his own plans, which are not revealed to the viewer. Gideon agrees immediately and the two shake on it. Unbeknownst to Gideon, Mabel and Soos witnessed the deal in the forest, and get Dipper's help to follow him into Stan's mind.
Once inside Stan's head, Bill confronts the trio, and brags that he knows what they're all thinking. To prove his statement, he summons Xyler and Craz from Mabel's imagination. He tricks Mabel and Soos into looking for the memory of Stan's safe combination first, knowing they'd lead him straight to it. At some point Soos is separated from everyone else, and Bill takes his place. Once they find the correct memory he takes it and nearly escapes with it. But while he reads the combination out loud to Gideon (to whom he was connected), Mabel shoots the memory door into another memory of thebottomless pit with a nyarf dart. Gideon breaks off their deal, to Bill's fury. Bill turns his anger toward Mabel and Soos by bringing their nightmares to life and killing Xyler and Craz.
Dipper returns in a timely manner and tells Mabel and Soos that while they are in Stan's mindscape they can do whatever they want. They battle Bill and he is nearly defeated. And just as though it seems he will be forced out of Stan's head, he puts a stop to everything instead. Impressed, he decides to let them go, and after warning them of a mysterious darkness that will change everything they care about, he tells them that he'll be watching them. He leaves in a wheel almost identical to the one that appears in his entry in book 2.
Season 2
Bill reappears again in "Sock Opera" for the first time in Season 2, when Dipper is trying to figure out the password for the Laptop from "Into the Bunker." He offers the laptop's password in return for a favor he wants, but Dipper refuses the offer. Later, at the moment the laptop is on countdown for complete data erasure after too many failed password entries, he appears again and Dipper accepts the deal of trading a puppet to obtain the password. Bill takes over Dipper's body as his "puppet" and destroys the laptop. He then follows Mabel to her puppet show in pursuit of Dipper's journal, which is being used as a prop in the show. After Mabel has been informed of Dipper's body having been stolen by him, he finds her with the journal as she is retrieving it for Dipper. He almost swindles her out of it but ends up in a fight with her. He ends up losing because Mabel uses Dipper's physical weakness and exhaustion to her advantage. As he collapses, he is thrust out of Dipper's body.
Bill possesses the Dipper puppet afterward and says that he will return. However, Mabel activates the pyrotechnics, destroying the puppets.
In "Northwest Mansion Mystery," he appears on a tapestry hovering over a forest fire with two men either begging for mercy or worshiping him while skeletal corpses are underneath them, foreshadowing bad events.
At the end of "The Stanchurian Candidate," after a prison-bound Gideon fails to get his father elected mayor, he is shown to have drawn Bill Cipher's wheel on his cell wall and hidden it behind a cat poster. He tears the poster away and completes the drawing with the eye before telling it he's ready to make a deal.
In "The Last Mabelcorn", Bill appears in Ford's dream, taunting Ford and telling him to keep the interdimensional rift safe, lest terrible things happen. He then appears in multiple flashbacks revealing his past with Ford and again at the end claiming that while he can't possess anyone inside the Mystery Shack, he can still choose someone from the outside. In the past, Bill and Ford were partners. Bill could enter Ford's mind at any time, and with his help, Ford built the portal. However, after Fiddleford came out of the portal, traumatized by the horrifying things he saw, which were Bill's actual plans, Ford realized Bill had lied to him. He confronts Bill, who reveals his plan to merge the Nightmare Realm he comes from with the real world, causing the apocalypse. Ford breaks off the partnership then and there. In the present, Bill watches as Ford and Dipper manage to block him from entering the Mystery Shack. Undeterred, Bill decided to possess someone outside the shack.
Against Sora's Team
Once his enemies joined the team, he started to follow and have his "fun" with Sora and the team. After forming the Forbidden Fiends, Bill gained a Human form