"Bill Cipher" is a triangular dream demon formerly existent only in the mindscape who wished to gain access to the real world. He has been running amok in Gravity Falls, Oregon since being summoned by Stanford Pines over thirty years ago. He is known for his mysterious demeanor and sadistic humor. He is the main antagonist of Gravity Falls, although he doesn't play a central role in the series until the penultimate Season 1 episode "Dreamscaperers".
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. His name and existence is deduced by taking all the capital letters in the cryptograms from Rumble's Revenge, to form the message: "MY NAME IS BILL."
Trillions of years prior to the events of the series, Bill Cipher originated from the second dimension. Bill, however, despised living there, describing it as a dimension of "flat minds in a flat world with flat dreams." He "liberated" his dimension by plunging it into burning chaos, along with everyone he's ever known, including his own parents.  He eventually took over a boiling, shifting intergalactic foam between dimensions: a lawless, unstable crawlspace known as the Nightmare Realm. However, due to the Nightmare Realm's lawlessness and lack of any consistent physics or rules, it was fated to collapse into itself eventually.  After coming to learn of a prophecy that stated he would merge the Nightmare Realm with the third dimension, Bill manipulated countless humans over the eons, determined to accomplish this.
Without a physical form however, Bill could only access the dreams of the dimension's beings. In order to make his dealings with mortals easier, He took on the name "Bill Cipher" as his real name would "evaporate one with an expression of horror and ecstasy on their face". Among his targets were the natives who lived in what would become the town of Gravity Falls, Oregon. He asked a shaman named Modoc to build an interdimensional gateway to the Nightmare Realm, but the result was made out of twigs. After Modoc learned of the prophecy that foretold of an apocalyptic event from his interactions with Bill Cipher, he lit himself on fire in an effort to stop Bill's reign. The valley was deemed a "cursed land" by the natives, who evacuated around 1000 AD. The natives discovered a way to defeat Bill by using a zodiac with ten symbols, and left behind a painting in a cave of their encounter with the demon, including how to summon him, and more importantly, a warning never to read it.
In the late twentieth century, a young man named Stanford Pines, who had spent the past six years investigating the town's plethora of unnatural creatures and oddities, hit a roadblock in his discoveries and was left without answers as to how the improbable aberrations of Gravity Falls had come to be. However, uncovering of a cave filled with cryptic hieroglyphics gave him hope of achieving answers, as the message foretold of an entity containing unending knowledge: despite the warnings against it, Ford repeated the incantation aloud, summoning Bill into the his mindscape. Bill recognized Ford's brilliant but cocky and insecure nature and his near-friendlessness as ideal conditions for manipulation, choosing to introduce himself to Ford as a muse who chose one brilliant mind every century to inspire. It was he who revealed to Ford that Gravity Fall's weirdness was caused by a rift between dimensions, through which the other side's weirdness leaked through. With Bill's assistance, Stanford drafted blueprints to create an interdimensional gateway beneath his home, and recruited his college friend Fiddleford McGucket for assistance. As Bill and Ford's partnership seemingly grew to friendship, Ford seemed to develop an obsession with Bill's powers, collecting triangular memorabilia such as rugs and statues, modeling his home's architecture in his image, converting his private study into a place of worship. He even allowed the demon to enter his mind; this, along with the amount of information he seemed to simply produce on the spot, made Fiddleford increasingly uneasy of the portal.
On January 18, 1982, Ford and Fiddleford performed their first trial with the active portal, which quickly went awry, as the dummy they intended to send through the portal became tangled with Fiddleford, sending him briefly through the portal head-first. Upon his return, an alienated Fiddleford muttered incoherencies before uttering a prediction about "the beast with just one eye", implying that he saw visions of Bill destroying Gravity Falls. He promptly abandoned the proyect afterwards.
The suspicion planted in him by Fiddleford led to a confrontation between Ford and Bill, during which Ford learned that Bill had tricked him, as the portal was meant to act as a gateway to the Nightmare Realm, allowing the demon to bring chaos and destruction into their universe. Horrified and betrayed, Ford shut down the project and attempted to destroy all knowledge of the portal, before accidentally falling through it himself. Bill either could not see Ford in the thirty years he spent lost in other dimensions, or didn't care to, as Ford would remark that they had not seen each other in many years. With the loss of his human pawn, Bill also lost physical access to the third dimension.
Events of Gravity Falls
"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 Bill. Gideon tells him to steal Stan Pines' 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 the bottomless 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 representation of the zodiac, almost identical to the one that appears in his entry in Journal 2.
Bill Cipher appears again in "Sock Opera," 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, 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 of the play, destroying the puppets and removing any vessel Bill could use to talk to the kids.
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 zodiac on his cell wall and hidden it behind a cat poster. The symbols on the zodiac have been changed around, and some have been altered. Gideon tears down the poster and completes the drawing by drawing Bill's eye before telling it he's ready to make a deal.
In "The Last Mabelcorn," Bill Cipher appears in one of Ford's dreams, telling him that he's been preparing for "the big day," going on to say that Ford can't keep the interdimensional rift safe forever. Bill throws a copy of the rift down to the ground, opening a red triangular portal in the sky and setting fire to Ford's mindscape. Ford yells at Bill to leave his mind, telling him he has no dominion in the real world. Bill leaves through the portal, telling Ford that "things change."
Far later in the episode, Bill appears in flashbacks as Ford explains his time spent with the demon to Dipper. 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 confronted Bill, who revealed his plan to merge the Nightmare Realm he comes from with the real world, causing the apocalypse. Ford broke off his partnership with Bill then and there, despite Bill's warnings that he couldn't stop the rift from happening. Ford shut down the portal and swore to never trust Bill again.
At the end of the episode, Bill watches from the Nightmare Realm as Ford and Dipper manage to create a "Bill-proof" barrier around the Mystery Shack by using moonstones, mercury and unicorn hair. Undeterred, Bill decides to possess someone outside the shack instead.
Near the end of "Dipper and Mabel vs. the Future," Bill approaches Mabel by possessing Blendin Blandin, recognizing Mabel's wishes of wanting summer to never end. Bill (as Blendin) convinces Mabel to give him the interdimensional rift, which he says can be used for making a "time bubble" that can make time stop. Mabel gives Bill the rift, which he promptly smashes with his boot. Bill reveals himself and leaves Blendin's body, knocking out Mabel with a snap of his fingers and initiating Weirdmageddon.
In "Weirdmageddon Part 1," after opening the rift, Bill gains a physical form and imprisons Mabel in a bubble. He introduces himself to the people of Gravity Falls, claiming to be their new ruler as well as introducing his friends to the people. The townsfolk refuse to submit, but Preston Northwest welcomes him instead, offering to be one of his "horsemen of the apocalypse." Bill thinks about the offer, but instead decides to disfigure Preston's face, creating fear in the people. He begins "redecorating" the town by unleashing Eye-Bats that petrify and abduct the townspeople, summoning the Fearamid, and sending out bubbles that instill madness in everything they touch. Bill recreates the opening theme song in the process.
When Bill and his friends prepare to cause havoc, Ford attempts to shoot Bill back into the rift with his quantum destabilizer, but misses. When Bill notices Ford and Dipper, he blasts the clock tower. Ford, pinned under rubble, begins to tell Dipper that there's another way to defeat Bill. He is cut short when Bill appears, towering over Ford. Bill captures Ford and presents him to his friends, telling them that Weirdmageddon wouldn't be possible without Ford. Bill makes an offer with Ford and tells him it's not too late to join his side. Ford refuses, so Bill turns him into a golden statue to use as a back-scratcher. Dipper, who has gotten back to street-level, yells that he's had enough. Bill flies over to Dipper, asking the boy what he could possibly do to defeat him in one shot. Dipper flips through Journal 3, trying to find Bill's weakness. With no answers, Dipper panics, and leaps towards Bill, trying to punch him. In response, Bill knocks Dipper backwards, causing him to fly into a tree. Bill then telekinetically seizes the three journals, burning them in front of Dipper, with two crippled pages surviving. Bill tells 8 Ball and Teeth that they can eat Dipper for a snack. Bill then converts a random car into a sleek getaway ride for himself and his other friends. The car flies away to the Fearamid leaving Dipper, 8 Ball, and Teeth behind.
Bill and his friends are later seen having a rave party inside the Fearamid. Suddenly, the Time Paradox Avoidance Enforcement Squadron, Blendin Blandin, and the Time Baby barge in, attempting to arrest Bill for possessing Blendin and almost destroying reality. Bill vaporizes the Time Police and Time Baby instantly, and the party resumes. 8 Ball and Teeth approach Bill, informing him they failed to eat Dipper. They ask him if he's worried about Dipper freeing Mabel, but Bill says he's not concerned, and that he has "someone on the case."
In "Weirdmageddon 2: Escape From Reality," Bill has been in power for four consecutive days. Most of the townsfolk have been petrified and stacked into a "massive throne of frozen human agony" for Bill. He announces his plan to take Weirdmageddon worldwide, and the demons make their way toward the edge of Gravity Falls. But instead of escaping to the rest of the world, they hit a strange force field-like energy dome that keeps Bill and his chaos stuck in the town.
Later in the episode, Bill is angered and unable to understand why he and his friends aren't able to extend their reach and leave Gravity Falls to dominate the world. He realizes that Ford is the only one able to understand the shield and contemplates his next move. He is interrupted by Keyhole, who informs him Gideon, Mabel's jailer, has failed to stop Dipper, allowing him and his group to enter Mabel's bubble. Bill is not worried by this, calling Mabel's bubble one of his most diabolical traps yet. He asks for Gideon and tells Keyhole to take the day off.
In "Weirdmageddon 3: Take Back The Falls," Bill reverts Ford from his gold state. He explains to Ford that he, along with the rest of his friends, can’t escape Gravity Falls. Ford thinks that this is due to a natural magnetism attracting weirdness to Gravity Falls, the event he’s studied for years, a force so strong that it forms a barrier that prevents that weirdness from going outside the town. He says there’s a way to break this barrier, but he’d never tell Bill. Bill tries to persuade Ford by telling offering him unlimited power in a world without restrictions or laws. Ford again refuses, calling Bill insane. Bill decides to find the equation needed to break the barrier in Ford’s mind. However, Ford reminds Bill he can’t unless he makes a deal with him. Bill decides to try and find Ford’s weakness and force him to make the deal, chaining him up further.
Bill is later seen torturing Ford by blasting him with lasers until he agrees to his deal. Though Ford is in pain, he still refuses to give in. Before Bill can start torturing Ford again, he is interrupted by the Shacktron, a gigantic mech created by Old Man McGucket, with the help of Dipper, Mabel, and various townsfolk. They converted the Mystery Shack into a powerful machine to fight Bill and rescue Ford, who knows Bill's weakness. Bill finds it "adorable" that the refugees are fighting back, and orders his henchmaniacs to fight them. However, his minions are quickly defeated by the Shacktron, and Bill is upset as Ford congratulates Dipper and Mabel for their efforts. Bill realizes Ford cares about the twins, and wonders if torturing them will be more effective than torturing Ford. Bill turns Ford back into a gold statue, and flies over to the Shacktron. He attempts to crush the Shacktron with a giant fist, but it remains intact thanks to the "Bill-proof" barrier surrounding the Mystery Shack. Bill becomes enraged and repeatedly punches the Shacktron. The refugees use the dinosaur attached to the Shacktron's left arm to tear out Bill’s eye and distract him. Realizing now is their chance to rescue Ford, a team composed of the twins, Stan, Soos, McGucket, Wendy, Pacifica, and Sheriff Blubs is ejected out of the Shacktron, using parachutes made out of Mabel's sweaters to land inside the Fearamid.
Everyone lands right next to the human throne, but Dipper is unable to figure out how to unfreeze everyone. Gideon Gleeful, trapped in a cage hanging from the ceiling, explains that Mayor Tyler is the load-bearing statue in the human throne, and if he’s pulled out, the whole throne will fall apart. When Dipper does so, it sets off a chain reaction. As the chair collapses, Gideon’s cage is knocked to the ground and breaks, freeing him. The residents are returned to normal, and Ford unfreezes as well. When Dipper and Mabel ask Ford what Bill’s weakness is, he explains that the way to thwart Bill is by using a zodiac with ten symbols. When each person that correlates with a symbol stands on a drawn version of the zodiac and they hold hands, it can create a force strong enough to vanquish Bill. Meanwhile, Bill is still fighting the Shacktron. It manages to pin Bill to the ground, but Bill realizes its legs aren't inside the unicorn barrier. Bill utilizes this weak spot to flip the Shacktron over, tear off a leg, and smash it into the Shacktron, sending it flying. Back in the Fearamid, the townsfolk that aren't represented in the zodiac run away, leaving only Dipper, Mabel, Soos, Wendy, Gideon, Robbie, Pacifica, McGucket, Ford, and Stan. For a moment, it seems that they will be able to complete the ritual. However, after Ford corrects Stan on his grammar, Stan pushes Ford, breaking the link. The two begin to fight as Mabel and Dipper try to stop them. While they’re distracted, Bill looms above them, having beaten the Shacktron and regenerated his eye.
Bill sends a wave of fire at them, burning the zodiac away. He also traps Stan and Ford, binding them with ropes. The resistance prepares to fight against Bill, but the demon snaps his fingers and turns everyone but the Pines into tapestries showing their screaming faces. Bill then imprisons Dipper and Mabel in a triangular cell. Bill says he’ll spare the twins if Ford lets him into his mind, giving him one last opportunity. The twins yell at Ford not to do it, causing Bill to angrily fly up to them. Mabel quickly takes out her spray can and sprays Bill’s eye, distracting him again and freeing Stan and Ford. While Bill’s distracted, Dipper takes out his size-altering flashlight and enlarges the cell, making it so him and Mabel can walk through. He and Mabel goad Bill into chasing them down a long hallway. As Bill moves to follow them, Stan and Ford try to escape. However, Bill places them inside a larger cell like the one he put the twins in. Bill then changes into a monstrous red and yellow form and chases the kids throughout the Fearamid, threatening to disassemble their molecules. After recapturing the twins, he gives Ford an ultimatum—let him into his mind, or one of the twins will be killed. Ford reluctantly surrenders as Stan objects. Bill removes the cell and ties up Stan. Ford’s only condition to the deal is that he lets his family go. Bill accepts as he shakes hands with Ford. Bill’s physical form turns to stone as his mental form goes inside Ford’s mind.
Ford’s mind is a bleak white landscape with a single wooden door. When Bill opens it, he’s greeted with Stan playing paddleball inside the Mystery Shack. Stan reveals that while the demon was chasing Dipper and Mabel, he and Ford swapped clothes and pretended to be each other so that Bill would enter the wrong mind. In the real world, Ford takes out the Memory Gun, setting it to completely erase Stan’s memory. In the mindscape, Bill tries to call the deal off as the door shuts and the room becomes enveloped in blue fire. Stan explains his mind’s going to be erased with Bill in it. Bill tries to escape and resorts to bargaining with Stan, but Stan doesn’t budge. Bill’s form heavily glitches out as he speaks backwards messages. Stan punches the weakened Bill into nonexistence as his mindscape becomes consumed by fire. Following Bill's defeat, everyone is freed from the tapestries. Outside the Fearamid, Bill’s henchmaniacs are sucked back into the portal, with the bricks of the Fearamid not far behind. The portal itself closes and explodes into a great shockwave, returning the entirety of Gravity Falls back to its own version of normal. The only thing that remains of Weirdmageddon is Bill’s petrified physical form.
After the credits, Bill Cipher’s petrified form is shown in live action, isolated deep in a forest.
Although Bill was erased from existence by Ford and Stan, it is strongly implied that he can revive himself somehow, as shortly before disappearing he relays a distorted message that when reversed says "A-X-O-L-O-T-L! My time has come to burn! I invoke the ancient power that I may return!"In one of the possible storylines of Dipper and Mabel and the Curse of the Time Pirates' Treasure!: Select Your Own Choose-Venture, Dipper and Mabel end up in "the time and space between time and space," where they encounter a creature called the Axolotl —a giant talking axolotl—, who lets each of them ask him a question. Dipper asks him "what [does he] know about Bill Cipher," to which he replies with a very revealing poem:
This suggests that, before being erased, Bill invoked the Axolotl to get redemption for his crime, and that there is one way to get absolved: he would have to take "a different form" in "a different time." That means that Bill could still be alive, paying for his crime. Though most of the book's content is non-canon, because it follows a "choose your own adventure" format (it has many possible endings), this answer could be the "one enormous 'canon' secret" Alex Hirsch said it contains. The encounter with the Axolotl ends with him sending Dipper and Mabel back in time, without any memories of what happened.
Sixty degrees that come in threes.
Watches from within birch trees.
Saw his own dimension burn.
Misses home and can't return.
Says he's happy. He's a liar.
Blame the arson for the fire.
If he wants to shirk the blame,
He'll have to invoke my name.
One way to absolve his crime.
A different form, a different time.
Bill's potential return is further implied in the Cipher Hunt, where Alex Hirsch warns the treasure hunters never to shake the statue's hand, even though he should be dead (Ironically, the group that found Bill shook his hand), as well as Stanley's final message to the hunters, beginning with him singing "We'll Meet Again" (what Bill sang in the finale) and even urging the hunters to shake Bill's hand as a congratulations, implying that Bill is alive and using his body to speak at periods.
Even more unsettling is the fact that the photo of Alex's voices (Stan, Soos, and Fiddleford) can be illuminated by a blacklight - this reveals Bill, alive, saying "STAY PARANOID!" and adding his signature. This also happens when one illuminates the photo of the Mystery Shack cast standing around the seemingly lifeless statue - doing so causes the cast and the statue to glow while the words "TRUST NO ONE!" appears.
It is unknown if the Hunt is canon to the TV series.
Bill is a cunning, eccentric, insane, psychopathic, and physically irreverent demon who finds most things amusing. He's outrageous and outlandish, as well as a quick talker and thinker. Though he may come across as simply annoying, he shouldn't be underestimated; for when he is angered, he's a force to be reckoned with as he will unleash his near-omnipotent powers on those unfortunate enough to make him angry. When accused of being insane, Bill proudly agrees with the statement.
Bill is not one who believes in rules. Instead, he follows his own selfish philosophy which means doing whatever he wants without care for the consequences. He thinks of laws and physics as senseless and displays an irresistible urge to break those rules down by causing absolute chaos however he can. The lives he ruins hold no merit to him and he finds amusement in tormenting and turning people's worlds upside-down. He also sees reality as an "illusion," and values its destruction.
When possessing Dipper's body, Bill is shown to be rather masochistic, hurting himself in various ways for the thrill of it, exclaiming that "pain is hilarious". He seems to have little knowledge about the human body, specifically its physical limits. This comes back at him when he fights Mabel over Journal 3, falling down exhausted.
In "Weirdmageddon Part 1," he shows sadistic tendencies, such as when he shuffles "the function of every hole in Preston Northwest's face" and in "Weirdmageddon 3: Take Back The Falls" when he decides to kill one of the Pines twins "just for the heck of it."
Bill is a yellow, triangular creature who bears a strong resemblance to the reverse side of the Great Seal of the United States, which in turn consists of the Eye of Providence and an unfinished Egyptian pyramid. He has a single large eye rimmed with four short black lashes on the 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 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 move along the perimeter of his body without any difficulty. He occasionally carries a small black or yellow cane. The lower part of his body has a brick-like pattern of lines. He has no fixed size, and he has been shown to be as small as a hand and much larger than the Mystery Shack. When he gets mad, he turns red and his eye glows a light red.
Even though Mabel calls Bill "isosceles monster" in "Dreamscaperers", in the book Dipper and Mabel and the Curse of the Time Pirates' Treasure!: Select Your Own Choose-Venture it is strongly implied by the Axolotl's poem about Bill that he's an equilateral triangle: the first verse says "sixty degrees that come in threes", and equilateral triangles have three internal angles of 60° each.
To summon Bill Cipher, one needs a picture of their intended 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" in reverse 5 times. 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: "Videntis omnium. Magister mentium. Magnesium ad hominem. Magnum opus. Habeus 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, which also protects against his chaos when he gains corporeality. 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 subject's 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.
The Cipher File
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 (with a picture of Bill).The page ripped out of a book ("book excerpt" on images to the right) reads:
Pyramids, also known as square-cones, are found all around the globe and have deeply mysterious origins. Modern engineers marvel at their seemingly impossible construction, but many don't realize they're actually just the skeleton remnants of an ancient race of large triangular dinosaurs who had very blocky bones. The Cycloptostoneosaurus was a feared predator and roamed the plains of North Africa where it subsisted on a diet of warthogs and meerkat, is made tender by their carefree lives and trouble-free philosophies. The reign of the pyramid continued well into the 18th century where a young George Washington once saw one on summer vacation and swore that he would found a nation with the sole purpose of putting an image of it on the back of dollar bills. Pyramids today are mainly tourist attractions and setting for conspiracy movies. Like that one where the guy has to steal the Declaration of Independence. You know the one, "Conspiracy Hank Goes Overboard." If you ever get a skateboard go to Egypt and try riding down the side of a pyramid. I hear that's really encouraged.
In Journal 3, behind Bill's name, is a message encrypted with a symbol substitution cipher. When decoded it reads: "Liar. Monster. Snappy Dresser."
Bill is described as a "dream demon", displaying some of the characteristics historically attributed to demons, like the creation of contracts.
In the Mindscape
As Bill can't acces the third dimension physically at first, summoning him seems to put the people around him into a sleeplike trance that allows him to manifest. The people observing are unaware they've fallen asleep until Bill leaves, after which they usually awake with a jolt. Bill can also enter another person's mind through their dreams.
Once within the trance, or within someone's mindscape, his powers are vastly magnified, becoming capable of changing his appearance, changing the appearance of other people's dream selves, and changing the area at will . He can also pluck information from any others who are also inside and bring those ideas and images to life, as was the case with Xyler and Craz. Bill can communicate with his summoner using his body as the screen of a video phone; he can also use his whole body as a projector, displaying past and future events as live video footage.
As Bill often mentions, he is close to omnicient: he knows the truth of many well-known conspiracies and can see the future (such as the destruction of the Gideon-bot and that Gideon Gleeful would go to prison), an ability he often flaunts by offering to tell a person the exact time, date and cause of their death - he seemingly predicted Ford's death, by heart attack at the age of 95, upon first meeting him. Bill has the ability to see things through the eyes of any image of himself , which is why his image appears hidden throughout many items and places in Gravity Falls.
Bill also has the ability to remove people's souls from their bodies, taking posession of the empty body himself. The real owner of the 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 revealed when Dipper used a puppet of himself to communicate with Mabel while stuck as a disembodied spirit.
Despite his vast knowledge and abilities, Bill has limitations. He must be summoned in order to appear first: he vanished from Gravity Falls once Ford disappeared, and only manifested again after Gideon summoned him once more, even remarking that he hadn't been there "in a while". He can only access bodies and conscious minds if he is allowed to through a contract, which involve agreeing on certain terms and shaking Bill's hand. Being well aware of this, Bill is known to twist and manipulate the words of these contracts for his benefit. When taking possesion of a mortal body, Bill becomes limited to it, subject to pain (which he finds "hilarious"), exhaustion, and even the host body's particularities, as evidenced when he was shown to react to Dipper's ticklish areas while in Dipper's body.
His vast powers are also strictly limited to dreams and the mindscape: his powers do not migrate into his host body and can't affect the physical world.
In Physical Form
After smashing the interdimensional rift and creating a gateway from the Nightmare Realm, Bill became incarnate, which allowed him to both exist and affect the real world.
In his physical form, Bill is nigh omnipotent, bringing inanimate objects to life and turning people into statues of the material of his choice. He can regenerate every aspect of himself, create everything from objects to elaborate pocket dimensions (like Mabel's prison bubble) and produce electric charges (shot from his eye). His abilities in this form also include: Apportation, Matter Manipulation, Mind Control, Reality Warping, Inter-universal travel, Time Manipulation, Dream Manipulation, Clairvoyance, Illusion Manipulation, Intangibility, Levitation, Molecular Manipulation, Nightmare Inducement, Possession, Precognition, Pyrokinesis, Size shifting, Telekinesis, Telepathy, Madness Inducement (can create bubbles that induce madness into whatever they touch), Regeneration, Fourth Wall Awareness (is aware of the real world and can "see" us), and Resistance to reality warping and space-time manipulation. He even surpasses Time Baby's powers, which he displayed by disintegrating him during "Weirdmageddon Part 1."
However, even an incarnate Bill discovered limitations in his power. Bill's physical eye proved particularly sensitive and took more time than the rest of him to regrow. Even while capable of vastly affecting the physical world, he still could not enter bodies or conscious minds without the contract-and-handshake process. Gravity Fall's bubble of weirdness also thwarted Bill's powers, as no amount of hitting or shooting at it dissolved the barrier, which stopped Weirdmageddon from advancing into the rest of the world.
The prophecy of the zodiac hung heaviest of all over Bill's mind. This prophecy explained that if ten particular individuals gathered in the circle designed by the ancients who had known Bill, they would be able to stop him; however, this would not come to pass if any of them broke the chain.
Despite this, Bill's own ego proved to be his most fatal flaw, as it led him to underestimate the "mortals": he failed to recognize Stan's trick, driven by the possibility of learning how to bypass the bubble over Gravity Falls, and did not realize he was at his most fragile while in the mindscape. His elimination also revealed that, while in the mindscape, he was as vulnerable to erasure via the memory gun as all other thoughts.
"It's funny how dumb you are!"
"Pain is hilarious!"
"Sure I am [insane], what's your point?"
"Remember! Reality is an illusion, the universe is a hologram, buy gold, BYE!"
"Hey, Soos, wanna hear the exact time and date of your death?"
The following are sightings of Bill and the Eye of Providence outside his physical appearance.
|"Gravity Falls Main Title Theme"|| Top left of the scrolling page.|
For a brief flicker at the end of the opening.
|In a page of book 2, hidden in one frame at the end of the intro.|
|Multiple episodes|| The 'A' in Mystery Shack over the main entrance.|
First seen in "Tourist Trapped."
| On the rug in the Mystery Shack's gift shop.|
First seen in "Tourist Trapped."
| The red stained glass window on the main attic floor.|
First seen in "Tourist Trapped."
|"Headhunters"||The window in the room which stored the forgotten wax figures, and melted Wax Abraham Lincoln.|
|"The Hand That Rocks the Mabel"||"Bill Jar," a glass jar holding Gideon's paint brushes. In upper right corner of the image.|
|"The Inconveniencing"||The window under Wendy's hangout spot.|
|"Irrational Treasure"||On the right side of the negative twelve dollar bill.|
| "The Time Traveler's Pig"|
|On the back of playing cards.|
|"Fight Fighters"||On the screen of an arcade game.|
| "The Hand That Rocks the Mabel"|
|Carpet pattern, such as under the chair and to the front left of Gideon.|
|"Summerween"||On Dipper's shield.|
|"Carpet Diem"||On a tube of makeup-gel.|
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