Well, a cool plot might involve an antagonist getting hold of the love potion and using it to manipulate the townspeople to do their bidding. For example, Bill Cipher could use it to make the Pines family fight among themselves. Or perhaps a love potion is created by accident in a science experiment gone wrong in the Mystery Shack, and it starts to affect all the customers who come in. It could lead to some really wacky and unexpected pairings, like Soos falling for a random tourist.
One idea could be that a character accidentally drinks the love potion and falls for the wrong person, like Dipper falling for Gideon, creating a chaotic and humorous situation. Another could be a character using the love potion to win a popularity contest in Gravity Falls, but things go awry when too many people fall for them at once. Maybe a character tries to use the love potion to make their crush notice them, but it backfires and makes the crush avoid them instead.
A possible plot is that Mabel discovers a hidden stash of love potions in the forest. She decides to use one on Pacifica to make her nicer, but instead, Pacifica becomes overly obsessed with Mabel. This causes all sorts of problems as Mabel tries to reverse the effects. Meanwhile, Dipper is trying to solve the mystery of where the love potions came from in the first place, and he uncovers a secret society in Gravity Falls that has been using love potions for centuries to control the town's relationships.
One idea could be that the characters from Reverse Falls accidentally cross over into the Gravity Falls universe. They might initially be seen as threats by the Gravity Falls gang, but then they realize they have to work together to solve a mystery that threatens both universes. For example, a powerful and ancient evil that can only be defeated if they combine their unique skills and knowledge.
One plot idea could be that the characters from Gravity Falls enter the Pokemon world. They could go on a journey to become Pokemon trainers, facing challenges like gym battles and Team Rocket - like villains. For example, Dipper and Mabel could each catch their favorite Pokemon and compete in Pokemon contests.
One idea could be that the characters from Gravity Falls end up in the FNAF world. Dipper might be intrigued by the mystery of the haunted animatronics and try to solve it using his journal. Mabel could befriend the more friendly - looking animatronics, like Chica, and try to make them cute accessories. Another plot could involve the FNAF villains getting loose in Gravity Falls and the Pines family having to use the town's unique magic to stop them.
One idea could be that Dipper and Mabel end up in the Undertale universe. They might meet Sans and Papyrus. Dipper could be intrigued by the magic system in Undertale and try to study it, while Mabel would probably befriend the friendly monsters right away. Maybe they get involved in the conflict between humans and monsters in the Undertale world and use their Gravity Falls knowledge to find a new solution.
Another interesting plot could be that there's an ancient vampire curse in Gravity Falls, and Dipper gets caught up in it. He has to find a way to break the curse before it's too late, and in the process, he discovers more about the history of the town and its connection to vampires. This could involve teaming up with Mabel and other characters from the show to solve the mystery.
Perhaps there is an ancient evil that threatens both Gravity Falls and Hilda's world. The characters need to combine their unique skills and knowledge. Dipper's knowledge of the strange and supernatural from Gravity Falls, along with Hilda's experience with the magical creatures in her world, would be crucial. They could start by gathering allies from both worlds, like Wendy and David. Then, they embark on a journey to find the source of this evil and a way to stop it. This would involve a lot of exploration, mystery - solving, and character development as they learn from each other.
One idea could be a Gravity Falls and Steven Universe crossover. Dipper and Mabel could meet Steven and the Gems. Maybe they'd team up to solve a mystery that involves both Gravity Falls' strange phenomena and the Gem-related threats. It would be cool to see how the different magical elements interact.
Another plot could involve Harry Potter himself. After defeating Voldemort, he feels a strange pull towards Gravity Falls. There, he meets the Pines family and discovers that there are new threats lurking in this strange town. Harry uses his skills as a wizard, like his Patronus charm, to fight off the supernatural entities in Gravity Falls, while also learning about the unique magic that exists there.
One idea could be that Danny Fenton and the Mystery Twins, Dipper and Mabel, cross paths while investigating a supernatural mystery that involves both the Ghost Zone from Danny Phantom and the strange anomalies in Gravity Falls. Maybe a powerful ghost has escaped into Gravity Falls and is causing chaos there, and Danny has to team up with the twins to stop it.
One idea could be arriving in Gravity Falls right during the Weirdmageddon event. You could team up with the Pines family to fight Bill Cipher. Another could be getting transported into the past of Gravity Falls, like when the town was first founded, and uncovering long - lost secrets. Maybe you become a new character in the Mystery Shack and have to deal with the daily weirdness that comes with it.