Well, one idea could be that the characters from Don't Starve end up in Gravity Falls. The strange and magical elements of Gravity Falls would be a huge challenge for the Don't Starve characters who are used to their own, albeit also strange, world. For example, Dipper could try to help Wilson figure out how to get back to his world while they both deal with the mysteries and threats in Gravity Falls.
A more light - hearted plot could involve the characters from both universes coming together for a big celebration or competition. Like a cooking competition where the Gravity Falls characters use their wacky ingredients from their world, and the Don't Starve characters use their survival - based cooking skills. Along the way, they learn about each other's cultures and make new friends.
Maybe the Gravity Falls villains like Bill Cipher could end up in the world of Don't Starve. This would create chaos as he tries to manipulate the already difficult situation in Don't Starve. The survivors in Don't Starve would have to use their survival skills along with the knowledge of Gravity Falls' magic (if they can figure it out) to stop Bill. It could be a really intense and action - packed plot.
A cool plot might involve the Pines family taking a trip to Mewni. Dipper is intrigued by the magical creatures and starts researching them, while Mabel befriends some of the more friendly magical beings. Meanwhile, Star has to deal with the chaos that the Pines family brings, and they all have to work together when an old enemy of Star's resurfaces and targets the humans as a way to get to her.
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 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 possible plot could be that Steven and the Crystal Gems end up in Gravity Falls. They could team up with Dipper and Mabel to solve a mystery that involves both the magic of Gravity Falls and the Gem technology. Maybe there's a Gem hidden in Gravity Falls that has been causing strange phenomena, and together they have to find and deal with it.
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.
One idea could be that the characters from Gravity Falls end up in the Don't Starve world. Dipper and Mabel could try to use their mystery - solving skills to figure out how to survive. Maybe they meet Wilson from Don't Starve and together they try to find a way back home while also dealing with the various threats in the Don't Starve world like hounds and the dark." ,"Answer2": "A plot could involve a strange portal opening between Gravity Falls and the Don't Starve universe. The Pines family, including Grunkle Stan, get sucked in. In this new world, they have to adapt to the rules of survival. They might discover that some of the creatures in Don't Starve are related to the mysteries in Gravity Falls. For example, the shadow creatures in Gravity Falls could have a connection to the dark forces in Don't Starve. They then embark on a journey to close the portal and return home." ,"Answer3": "Perhaps the magic in Gravity Falls somehow gets intertwined with the magic of the Don't Starve world. Characters like Bill Cipher from Gravity Falls could find a way to manipulate the Don't Starve world to his advantage. Meanwhile, the survivors in Don't Starve have to team up with the Gravity Falls characters to stop Bill. This would create a lot of interesting interactions as the Gravity Falls characters are used to a different kind of danger compared to those in Don't Starve. There could be a battle of wits and powers between Bill and the combined forces of both universes.
Another option is FanFiction.net. However, the quality can vary a great deal. Look for stories with high review scores and lots of favorites. Sometimes, you might also find some crossover fanfictions on Tumblr. Some fans post their works there, or they might reblog interesting ones they've found.
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.
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.
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.