Billboard
Billboard is a CURSED board featuring Bill Cipher.
Anyone in possession of the Billboard will be sentenced to eternal damnation!!
Origin
The Billboard was first discovered in the ancient year of undefined when undefined.
How it possess you
Have you seen the episode?? If not then too bad get spoiled dickface
In the Gravity Falls Library, Mabel and Dipper are finally able to open the laptop they found in the bunker after Soos had fixed it. Unfortunately, they are stopped from accessing the contents because it's protected by an eight letter password. Annoyed, Dipper begins to attempt cracking the password with Mabel, but she is distracted by puppeteer Gabe Bensen, who is performing for children on the wonders of reading. Mabel chats him up, telling him she has a love for puppets as well. Gabe is glad to find someone who is as "puppet crazy" as he is and asks her when her next puppet show is. Put on the spot, Mabel makes up a quick story and details the show in next week.
Mabel requests Dipper's help, promising she'd help him crack the password once they finish the preparations for the last minute show. Dipper reluctantly agrees, eager to finally discover what the laptop holds as he leaves the library with Mabel, unaware that a familiar shadow is following them.
Over the next few days, Mabel, Dipper, Wendy, and Soos make numerous puppets. In the meantime, Dipper continues to attempt cracking the password at night, depriving him of sleep-- failing repeatedly. The night before the show, while Mabel is content with her puppet progress, Dipper continues to grow frustrated. As she gets ready for bed, Dipper decides to head for the roof and try a little longer. Furious with the constant error sound the computer makes with every wrong entry, he considers that there must be a clue or shortcut to make the laptop work, when he is surprised by none other than Bill Cipher. Bill toys with Dipper before offering to give him hints on how to unlock the laptop. Bill would help Dipper if he agrees to "a small favor." Dipper refuses, the events of "Dreamscaperers" fresh in his mind. Bill tells Dipper that the offer will still be open, and he'll be ready to make a deal right before Dipper wakes up screaming.
In the kitchen, Stan is ignoring Mabel who is trying to get his attention with the puppet version of him. Stan continues to purposefully be oblivious to what she's been doing all week. Dipper tiredly takes Mabel aside and informs her of his encounter with the "triangle guy." Mabel reassures him that she's ready to help Dipper that day after passing along her puppets to her production crew, Candy and Grenda. However, this plan falls through when Gabe unexpectedly shows up, nitpicking a puppet show of another girl's he attended the night before. Feeling a rise in quality and pressure, and seeing her team's mishaps, Mabel decides to continue working on the show. Dipper angrily points out her promise and how breaking it isn't worth her obsession with her crush-of-the-week. However, Mabel throws the phrase back in his face and tells him that he's the one who's obsessed. She insists she'll help him after the show, but fed up and disappointed Dipper heads to the attic to crack the code himself.
However, the laptop, having received the incorrect password too many times, prepares to initiate a data wipe in five minutes. Just as Dipper flies into a panic, Bill Cipher reappears, giving Dipper an ultimatum: Accept the deal, or have the laptop's secrets erased forever, and all Bill wants is a puppet. Dipper suspiciously continues to reject the offer, telling Bill that Mabel worked really hard on puppets. Bill slyly reminds Dipper of all the times he has sacrificed his wants for Mabel, who has never returned the favor. Moreover, he tells Dipper that he just needs one puppet, of which there is a surplus of anyway. As the laptop continues to count down the seconds, the temptation pushes Dipper over the edge and he agrees.
As they shake hands (closing the deal), Dipper asks Bill which puppet he wanted. Bill mockingly ponders his answer before turning on Dipper and takes possession of his body and kicking Dipper's consciousness out. Dipper, now in a ghost-like form is shocked as Bill stomps on the laptop, smashing it to pieces. He reveals that Dipper was the puppet he wanted and that Dipper "had come way too close to figuring out some major answers," and wanted Dipper out of the way. He proclaims that now all he has to do is destroy Journal 3 and Dipper will be unable to stop his "big plans."
That's essentially how it possesses you.
How to defeat
You cannot. It is an impossibility. You could however try trapping the billboard into someone's mind and erase their mind?? Myabe that works?? 
Gallery
There is no gallery. Go home.