Bill is an extradimensional dream demon capable of warping reality and seeing into other dimensions. Appearing typically as a dapper, one-eyed yellow triangle, he harbors a deeply chaotic and sadistic nature beneath a playful exterior. He attempts to trick the reader into making a deal with him by recounting his historical efforts to conquer Earth.

Stanford is a brilliant researcher who isolated himself in Gravity Falls to study its anomalies. Driven by ambition and a sense of profound intellectual loneliness, he became an easy target for Bill's manipulation early in his career. He now leaves cautionary warnings to protect others from falling into the same traps he did.

Stanley is Stanford's hotheaded and deeply loyal twin brother. He runs the Mystery Shack tourist trap in Gravity Falls and acts as a protector for his family. He remains entirely immune to Bill's trickery and openly mocks the demon's attempts at intimidation.

Dipper is an anxious twelve-year-old who spends his time exploring the strange phenomena of Gravity Falls. He carries a deep sense of responsibility and worries about his family's stability, though he stands firm against supernatural threats when necessary.

Mabel is Dipper's eccentric and fiercely loving twin sister. Her mind is a colorful landscape guarded by imaginary protectors, making her immune to Bill's typical methods of psychological manipulation. She approaches cosmic threats with humor and unpredictability.

Fiddleford is a brilliant inventor and Stanford's former best friend who moves to Gravity Falls to build a multidimensional portal. Initially rational and deeply caring, his proximity to Stanford's dangerous research eventually exposes him to immense psychological stress.

Thurburt is an initially pleasant copywriter who makes a deal with Bill to achieve career success. After realizing the danger of his bargain, he founds the Anti-Cipher Society to banish the demon, risking his reputation to warn others.

Chronelius Infinitum Titanicus the Infinitieth, or Time Baby, is the last survivor of the extinct Chrono-Giants. He leads a patrol attempting to stop anomalies from damaging Earth's timeline.

An Indigenous spiritual leader who initially befriends Bill and exchanges knowledge with him. After receiving a vision of Bill's true intentions, he uses magic to banish the demon and creates a prophecy to ensure his defeat.

Xgqrthx is a medieval warlock who accepts Bill's help with his personal life. Instead of building the portal Bill demands, he uses unicorn hair to trap the demon in an orb.

Mary is a Puritan woman living in misery who accepts magical power from Bill to escape her oppressive life. She uses her newfound abilities to punish her enemies.

Elias is an early twentieth-century animator whose boring cartoons are revitalized when Bill influences him. He eventually realizes Bill's evil nature and commissions a song to banish the demon.

Soos is a loyal friend to the Pines family who works at the Mystery Shack. His inner thoughts reveal a deep desire to be officially adopted into the Pines family.

Wendy is a teenager in Gravity Falls whose private dreamscape reveals hidden vulnerabilities, specifically her thoughts about her mother.

Tinsley is an excommunicated priest who joins the Anti-Cipher Society. He attempts to perform an exorcism on Bill but ends up briefly possessed.

Horace is a strongman who falls victim to Bill's trickery and joins the Anti-Cipher Society to help banish the demon from human minds.

Pacifica is a resident of Gravity Falls who harbors deep-seated guilt. Her dreams involve an inability to wash blood off her hands, highlighting her internalized pressure.

Robbie is a local teenager whose inner dream life focuses mainly on hiding his original hair color from the world.

Gideon is a young resident of Gravity Falls whose mindscape is documented by Bill. His private embarrassments are used by Bill as entertainment.

Sheriff Blubs is one half of the Gravity Falls local law enforcement team. His dreams center entirely around his deep bond with his deputy.

Deputy Durland is the enthusiastic local police deputy. His inner thoughts revolve exclusively around his connection with his partner.