Gravity Falls: Lost Legends

Gravity Falls: Lost Legends is the first official Gravity Falls comic with new original content. It was announced at D23 on July 14, 2017, at Alex Hirsch and Daron Nefcy's panel promoting Gravity Falls: Journal 3 and Star and Marco's Guide to Mastering Every Dimension, respectively. It was released on July 24, 2018.

Plot
The book is presented as a series of stories told by Shmebulock, who was placed under a warlock's curse to say his own name, but every thousand years, is able to speak coherently in English.

Face It
Pacifica comes by the Mystery Shack to peek at the Journals to see if there's a way to get rid of a wrinkle on her face. She summons a demon who swipes away Mabel's face, and it is up to Dipper and Pacifica to get it back.

Comix Up
Soos brings a bunch of comic books to the Mystery Shack, but Grunkle Stan locks them away in Ford's cursed chest. In a fourth-wall breaking twist, Stan finds himself trapped in a world of comics, so Dipper, Soos, Mabel, Ford and Wendy go into shifting comic styles to rescue him.

Don't Dimension It
In the aftermath of Weirdmageddon, the Pines family wander through Gravity Falls to see if there are any dimensional rifts left over. While playing with Waddles, Mabel finds herself sucked into the multiverse, were she finds herself among many different Mabels.

Pine Bros Mystery
In the year 1960-something, young Stan and Ford attempt to catch a supernatural being suspected of stealing Filbrick's precious medal.

B&N Edition
The Barnes & Nobel version of the book has an extra chapter, titled Soos's Comic Corner, narrated by Soos. It includes 16 extra pages of behind the scenes sketches and notes, detailing many of the pages, and exploring secrets within them.

Cryptograms
See List of cryptograms

References to the series

 * Dipper's original hat that he lost to a gnome in "Tourist Trapped" is on one of Shmebulock's bookshelves.
 * "Face It"
 * There are a number of references in The Crawlspace.
 * A former member of the Blind Eye Society is seen selling memory canisters.
 * The Hand Witch is seen selling hands.
 * A pirate Lilliputtian is seen stealing an egg from a question quail that is mentioned in Journal 3.
 * A plaidypus and a geodite, which are also mentioned in the journal, appear as well.
 * A crow can be seen holding the Mystic Amulet used by Gideon in "The Hand That Rocks the Mabel".
 * The gnome that was selling fairy dust in "The Last Mabelcorn" can be seen selling some to a unicorn.
 * The candy monster can be seen chewing on a banner.
 * One of the wanted posters has a silhouette of Wax Larry King.
 * Some Eye-Bats can be seen flying around.
 * A Gremloblin can be seen passing by the barrels that Dipper and Pacifica are hiding behind.
 * Dipper frustratedly states that he's never kissed anyone before, referencing the reverse CPR scene from "The Deep End."
 * Dipper references the events of "Northwest Mansion Mystery."
 * Dipper uses the President's Key that he got from Quentin Trembley in "Irrational Treasure".
 * Some of the faces seen in Mr. What's-His-Face's collection include Blind Ivan, the Summerween Trickster's mask, Deputy Durland, and Alex Hirsch.
 * "Don't Dimension It"
 * Mabel references the ending of "Dipper and Mabel vs. the Future."
 * The finger monster that attacks Mabel in the Nightmare Realm resembles the description of the "60-foot ball of fingers and teeth" that Bill sicced on Ford when he first arrived in there which is mentioned in Journal 3.
 * The interdimensional trucker brings up Ford's criminal record across the multiverse as described in Journal 3.
 * One of the dimensions that the trucker brings up is Lottocron Nine, which is where Ford got his infinity-sided die.
 * The trucker also has a pair of fuzzy infinity-sided dice hanging from his rear-view mirror.
 * The pine tree journal that Mabel gives to Dipper, which she got from an alternate version of herself called Mabipper, resembles the one that Dipper mentions in Journal 3.
 * "Pines Bros Mystery"
 * Stan and Ford come across a pair called The Sibling Brothers.
 * Some of the items seen in the Pines Pawns shop include Stan's fez, the painting hanging in the attic of the Mystery Shack, and the scuba helmet in the shack's gift shop.
 * A ticket stub from Grandpa the Kid can be seen in Stan's scrapbook.

Trivia

 * Lost Legends was originally listed as XQWLWOHG PBVWHUB ERRN (which decodes to UNTITLED MYSTERY BOOK using the Caesar cipher) on Amazon Canada.
 * The front cover was revealed via a jigsaw puzzle, made of pine trees (the same style as seen on Dipper's hat), piece by piece on Twitter, Tumblr, and Facebook.
 * A version of Mabel resembling the character Morty from the Adult Swim series Rick and Morty is seen in the background of "Don’t Dimension It." In the Rick and Morty mobile game, "Pocket Mortys," there is a Morty who resembles Mabel Pines named "Girl Morty," who is very similar in appearance to the "Morty Mabel" seen in Lost Legends.
 * The book contains a secret code that leads to the secret site: The Shmeb you unlocked, which contains more information on various characters and small comics.
 * In one of the small comics what Dipper say can be decoded and comes out as "Cipher Lives", which is most likely a reference to the possible return of Bill Cipher
 * One of the files tells us that after the summer Tate McGucket is living with his father, Old Man McGucket, at Northwest Manor (now renamed McGucket's Hootenanny Hut)
 * It also reveals that his mother's name is Emma-May Dixon, formerly Emma-May McGucket
 * In the story "Face It" a former member of the Blind Eye Society is seen selling memory canisters belonging to various characters from the show.
 * These characters include: Tad Strange, Tambry, Abuelita and Gideon Gleeful.
 * Next to Gideon's canister, there is a tube labeled "Memories Rick S." This is likely a reference to Rick Sanchez from Rick and Morty who was played by Justin Roiland.
 * There is also a canister labeled "Mrs. Corduroy," which most likely refers to Wendy Corduroy's unseen mother.
 * In "Face It", there is a wanted poster with the silhouette of the character Eda from the upcoming Disney Channel series The Owl House.
 * In "Face It", the journal Mabel is reading shows a page that is titled, "Defense of the Dark Warts", most likely a reference to J. K. Rowling's series, Harry Potter, as Harry has a class named "Defense Against the Dark Arts". As below it are two words saying, "Expecto Psoriasis" likely derived from Harry's spell to defend against dementors, "Expecto Patronum".
 * Another reference to Harry Potter may be that in the dimension MAB-3L, there is a Mabel standing with their back to the viewer with the Hogwart's House, Gryffinfor's colors. In the Barnes & Nobel edition, it is stated that that Mabel's name is Gryffindabel.
 * The comic contains several elements that were not permitted in the TV series. Among these are:
 * The use of God's name in vain in phrases such as "Oh my God."
 * The use of the word "Hell."
 * Direct references to alcohol.
 * More suggestive themes, such as a character wearing a shirt with the semi-vulgar phrase "That's what she said" on it.
 * More direct cultural references, such as direct mentions of the comic character Marmaduke and the comic artist Stan Lee and a cameo from the pop culture character Slender Man.
 * The comic contains some references to the Gravity Falls fandom.
 * In the background of Schmebulock's library, there's a board reading "Shermie?", under which it says in cipher "age paradox?" and "time travel conspiracy?" which is in reference to the confusion about the baby in "A Tale of Two Stans" and its debate on the identity as Shermie due to the timeline.
 * There's also a fourth journal in the library under Dipper's original hat. Referencing the idea that there are more than 3 journals.
 * In "Face It" a creature resembling Slenderman makes an appearance trying to find money to buy Dipper and Pacifica. This is a reference to the urban legend that Slenderman appeared in "The Legend of the Gobblewonker" when it was, in fact, a result of photoshop.
 * In Journal 1 there is a page on "Paranormal Rashes", and depicts a rash that looks like Bill and is called, "Zodiacne". This is in reference to fan art depicting an adult Dipper having a tattoo of the Zodiac. Which was disproven by Hirsch himself when he said that Mabel is the most likely to get a tattoo. Which was also referenced in "Don't Dimension It" by Military Expert Mabel's 6-18 tattoo.
 * Stanbel in "Don't Dimension It" originated as a drawing on Hirsch's twitter and was jokingly drawn to "give you nightmares".
 * Chronologically, the four stories in Lost Legends occur as follows:
 * Pine Bros Mystery takes place in the early-to-mid 1960s, during Stan and Ford's childhood, around 50 years before the main events of Gravity Falls in the summer of 2012.
 * Face It and Comix Up both take place in the second half of Season 2, sometime among the episodes set between "A Tale of Two Stans" (sometime in August 2012) and "Dipper and Mabel vs. the Future" (August 22nd), as evidenced by Ford being present, whilst Weirdmageddon has yet to begin. The exact order or placement of the two stories in this time is unclear, though.
 * Don't Dimension It takes place during the final act of the episode "Weirdmageddon 3: Take Back The Falls," in the week between Weirdmageddon ending (August 25th) and Dipper and Mabel's 13th birthday (August 31st), as noted by a direct mention of the preceding event.