Weirdmageddon 3: Take Back The Falls is the only LGBT-themed episode and last episode of the season finale of Gravity Falls.
Twins Dipper and Mabel Pines are nearing the end of the summer stay with their great-uncle "Grunkle" Stan at the Mystery Shack in Gravity Falls, Oregon, which corresponds with their thirteenth birthday in a week. During their stay, they have befriended many of the town's residents and come to know the nature of several of the strange, paranormal events that have occurred within the town. They recently have been able to help Stan rescue his twin brother Ford Pines from a dimension he had been trapped in for several years after falling into a portal of his own design.
One of those paranormal events involves the chaotic dimensional being Bill Cipher; Cipher has long sought escape into the human dimension and has tried to do so in the past by manipulating humans in their dreams. When Ford had first moved to Gravity Falls, drawn there to study its strange phenomena, he had accepted Bill's help in exchange for the idea of the dimensional portal machine, giving Bill a foothold to potentially enter this dimension. Dipper and Mabel have faced and defeated Bill earlier in the summer.
In the first two parts of "Weirdmageddon", Mabel gets into an argument with Dipper after Dipper expresses his intention to stay in Gravity Falls and study under Ford, and runs off. In her sadness, she inadvertently turns over a bit of dimensional rift created from the portal to Blendin Blandin, a time-traveling ally, unaware he is under Bill's control. Bill uses the rift to fully open a portal from his dimension into the human one, calling forth the "Weirdmageddon". Bill quickly summons allies to take over Gravity Falls, calls forth his floating Fearamid castle, and petrifies most of the town's population, including Ford, to use as his throne. However, a protective shield around the town prevents Bill from spreading his power further, and he tortures Ford for information on how to free the barrier, which Ford refuses to give. Dipper, Soos, and Wendy are able to free Mabel from a dream-created prison after Dipper promises to return home with Mabel instead of staying.
Dipper, Mabel, Soos, and Wendy return to the Mystery Shack to find Stan, a handful of town residents, and several of the paranormal creatures they have befriended taking shelter there. The unicorn hair Ford lined the base of the Shack with protects them from Bill's powers. Stan, bitter that his brother never thanked him for rescuing him, believes they should just wait it out, but the others agree to mount a rescue mission. McGucket leads the survivors to transform the Shack into a giant mecha. They drive the newly dubbed Shacktron to the Fearamid and readily defeat Bill's allies. Bill comes out himself to fight, and the humans are able to tear out his eye, blinding him temporarily.
Dipper and Mabel lead a small group, including Stan, McGucket, Pacifica, Soos, and Wendy, aboard the Fearamid. They find a keystone in Bill's throne that once dislodged, de-petrifies the trapped humans. As most of the humans are evacuated from the Fearamid while Bill is still regenerating his eye, Ford spray paints a Zodiac wheel on the ground, having seen the image before in artifacts from earlier civilizations as a means to trap Bill. The wheel requires ten specific people, indicated by symbols on it that Ford only recently had deduced the meaning of, to stand on it and hold hands in a ring. This includes Dipper, Mabel, Soos, Wendy, Stan, Ford, McGucket, Robbie, Pacifica, and Gideon. Stan refuses until Ford both apologizes for allowing Bill a foothold on this word and thanking him for rescuing him. Ford reluctantly does so, but as Stan joins the wheel, Ford corrects Stan's grammar under his breath, and Stan and Ford get into a fight. Before they can be broken up, Bill appears, his eye having regrown and having defeated the Shacktron after finding its Achilles' heel.
Bill burns the Zodiac wheel, secures Dipper, Mabel, Stan and Ford, and turns the others into banners as to keep them from interfering. Bill threatens to kill Dipper and Mabel unless Ford allows him into his mind to find out how to escape Gravity Falls. Mabel sprays paint into Bill's eye, giving her and Dipper enough time to escape their confinement. Bill quickly gives chase. Left alone, Stan and Ford have a heart-to-heart talk. Although there is another way to defeat the demon by erasing him from someone's mind using the memory gun, Ford believes the only way to save the kids is to allow Bill into his mind since his own memories cannot be erased because of a metal plate in his head.
Dipper and Mabel lead Bill in a chase around the Fearamid but are eventually caught. Bill returns them to the throne room and again threatens to kill them in front of Ford. Ford agrees to allow Bill into his mind. Bill gleefully takes the offer, leaving his physical body which turns to stone, and entering a wholly white void with one door. Bill enters the door and is shocked to find himself in Stan's den of the Mystery Shack. Stan's consciousness there reveals he swapped places with his brother to trick Bill and is willing to sacrifice himself for the betterment of the world. In the real world, Ford reluctantly fires the memory-erasing gun at Stan. Bill starts to burn in Stan's mind and is punched out of existence by Stan before his memory is wiped. Without Bill, the portal to the other dimension closes, drawing in all of the fearsome creatures from it. Once closed, the town and its population revert to how they were before the Weirdmageddon started. Stan's family and Soos take him back to the nearly-destroyed Mystery Shack, hoping the sight of the building will help bring back his memories. Mabel finds her scrapbook and shows Stan all the times they had over the summer, which appears to slowly bring back Stan's memories, and soon he is back to normal.
A week later, many of the townsfolk join with Dipper and Mabel's friends to celebrate their birthday at the Shack. Ford offers Stan the opportunity to sail around the world for a year, a dream they had together as boys, but Stan would have to close down the Shack. The townspeople express their displeasure since the Shack draws tourists to their town. Ford offers the idea to put the Shack in the hands of Soos while they're gone, a plan everyone is happy with.
Later, Stan, Ford, Soos, Wendy, Candy and Grenda all see off Dipper and Mabel as their bus for home pulls up. They are about to board when Waddles, Mabel's pet pig, appears. Mabel doesn't want to let him go but knows their parents wouldn't allow it, but Stan decides that since he had to put up with the kids for the summer, their parents should be able to handle Waddles, and has Mabel take him with them. Wendy trades hats with Dipper and gives him an envelope to open later when he starts to miss Gravity Falls. The bus pulls away as the group wave goodbye. As Dipper and Mabel think back on their time in Gravity Falls, flash-forwards show Soos successfully running the Shack with his girlfriend Melody, and Stan and Ford on their sea trip, as well as the futures of several of the town's residents. When they pass the town's limits, Dipper opens Wendy's letter to find the signatures of all their friends in town, promising to see them next summer.
The credits of the show include a montage of twins' summer and eventual arrival in Piedmont, California. In a live-action post-credits scene, the stone body of Bill is seen, partially submerged in the ground in the woods.
Alasdair Wilkins of The A.V. Club claimed that it was the perfect ending to the series and awarded the episode an "A" for bringing back as many characters as possible, with even tertiary supporting characters getting their own little moment to shine. He applauded the way the episode exemplifies all Gravity Falls could be at its frequent best: It’s funny, emotional, beautiful, and terrifying in equal measure. According to him, "Back when Gravity Falls started out, it was pitched as a kid-friendly cross of The Simpsons, Twin Peaks, and The X-Files. I can think of no finer final tribute than to say it lived up to all the ridiculous potential implicit in that description … and ended up being something even better than that." In the end, he wrote that Gravity Falls had kicked off his AV Club reviewing career nearly four years earlier and was likely to be the only show he would ever get to review wire-to-wire, and so would always have a very special place in his heart for reasons that he couldn't imagine anyone else caring all that much about.
Max Nicholson of IGN gave the episode a 9/10 praising it's way of balancing all the characters and not leaving anybody out of the fun. He also enjoyed the little nods to the previous episodes of the show. According to him, "Weirdmageddon 3" was filled with laughs, excitement and heartwarming moments. In his review, "As animated series go, Gravity Falls was an excellent one, and it'll be sad to see it go. At the same time, I'm glad it ended while it was still fresh, so fans can remember it fondly."
The episode gained considerable press after its revelation that the characters Sheriff Blubs and Deputy Durland are gay, with coverage in LGBT-oriented sites as well. The pairing was revealed after the pair threatened anyone who asked too many questions about the events of Weirdmageddon with tasers. When they said they would zap them if anyone tells, Deputy Durland said that they're mad in power, then turned to Sheriff Blubs and they added, "and love." Hirsch previously said that he believed that he would be blocked from including LGBT characters in the show. He said, “I would love to, but I doubt they’d ever let me do it in kids' TV. But man, I would if I could.” This was the first time Disney XD and Disney Channel introduced a gay male couple, described as "Disney taking a huge step towards equality."