Definitely Dipper and Mabel from both universes. Their different personalities in Reverse Falls and Gravity Falls make for really interesting interactions. Bill Cipher is also a popular choice. His chaotic nature can add a lot of drama, especially when he interacts with the characters from the other universe.
I think Pacifica Northwest could be a great focus. In Gravity Falls, she has her own character arc, and in Reverse Falls, she might be even more complex. Seeing how she reacts to the situation when the two worlds meet can be very engaging. Also, Wendy is often a fan - favorite. Her laid - back attitude contrasted with the more intense Reverse Falls characters can create some cool scenes.
Mabel from Gravity Falls is also a popular character to pair. She could be paired with a character from Relativity Falls who has a different personality but shares her love for fun and creativity. Their interactions could lead to some really wacky and heartwarming scenarios, like planning a big party that combines the elements of both worlds.
One common theme is the clash of good and evil. Since Reverse Falls is often depicted as a more sinister version of Gravity Falls, when the two meet, there's a lot of conflict between the good-natured characters from Gravity Falls and the more devious ones from Reverse Falls.
I'm not entirely sure, but it probably features versions of Dipper, Mabel, and other main characters from Gravity Falls, just with different personalities or roles in this reverse version.
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 of the most interesting plot twists could be when the characters from Gravity Falls and Reverse Falls have to team up against a common enemy they didn't expect. For example, a new supernatural force that threatens both their worlds. This would force them to put aside their differences and work together, which is a big change considering the nature of the two settings.
One great 'Gravity Falls meets Reverse Falls' fanfiction is 'The Alternate Encounter'. It has an interesting plot where the characters from both universes interact in unexpected ways. The author does a great job of capturing the essence of both Gravity Falls and Reverse Falls.
It's a unique take on the Gravity Falls universe. It likely involves an alternate version of the story, with different character dynamics and plotlines in a visual novel format.
To create a compelling character interaction, think about the goals of the characters. In a crossover, a character from Gravity Falls might be trying to save their world, while a Reverse Falls character could be trying to take over the other world. When they meet, there will be conflict and negotiation. Let their different motives drive the conversation and actions. Also, use their unique abilities or powers in the interaction. If one can read minds and the other can manipulate shadows, how do those abilities play off each other when they interact? It can lead to really interesting scenes.
One interesting storyline could be the characters from both universes teaming up to solve a mystery that spans across their respective worlds. For example, Dipper from Gravity Falls and a character from Relativity Falls might work together to figure out a strange phenomenon that is affecting both places.
Dipper is definitely one of the most memorable. His curiosity and determination to uncover the secrets of Gravity Falls make him stand out. He's always getting into trouble while trying to solve the mysteries in the journal.