Character interactions are key. You want to see how the characters from different shows blend together. For example, if it's a crossover with Scooby - Doo, seeing how Shaggy and Dipper would react to the mysteries in Gravity Falls. Also, a good plot that makes sense for both universes. It can't just be a random mash - up.
Themes are important too. Gravity Falls has themes of mystery and family. If it's crossed over with a show like Avatar: The Last Airbender, the fanfic should blend the themes of bending and the mystery of Gravity Falls well. And of course, the fanfic should stay true to the essence of Gravity Falls. The unique humor, the creepy elements, all of that should be there in the crossover.
The world - building in a crossover fanfic is crucial. If it's a Gravity Falls and Harry Potter crossover, how do the magic of Hogwarts and the weirdness of Gravity Falls co - exist? It should be detailed and make you feel like both worlds are real and interacting in a logical way. Also, the pacing of the story should keep you engaged, not too slow or too fast.
Chapter 678, "The Biggest Connection in the Circle of Friends!", is the clearest early answer because it turns Jiang's situation into a concrete plot event. The chapter gives readers a real answer by opening on The landlord stood up, maintaining his smile, "Fifty-eight thousand,...
Chapter 619, "The Feast of Fish CP Is Indeed Real!", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. Early on, The storm grew fiercer until, at last, even the live broadcast had to....
Chapter 14 is the strongest chapter-level answer because it starts from Lin Manru had a rare good night's sleep. and follows through on But clearly, Lin Manru was unable to accept that her delicate daughter had....
Chapter 482, "Someone Might Need Me", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. Early on, Other people caught a glimpse of Zhao Lang's cold and stern face and.... By the end, In a moment, General Dino's face appeared on the large screen..
Chapter 870, "She is My Ex-Girlfriend", is the clearest early answer because it turns Xiao Xue's situation into a concrete plot event. The chapter gives readers a real answer by opening on Huo Shan couldn't believe it and covered her mouth in shock.
Chapter 619, "The Feast of Fish CP Is Indeed Real!", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. The chapter turns that into something concrete by moving from The storm grew fiercer until, at last, even the live broadcast had to...
The best chapter pointer here is Chapter 21, "Uncle Policeman, They Are the Ones Causing Trouble!". It opens with Jiang Li's clear and logical explanation had everyone stunned in place. and closes on But the implications could be different..
A practical answer is Chapter 2, because it turns the idea into a concrete scene. The chapter opens with On the top floor of the Financial Building, a gathering of dark clouds..., adds pressure through In my opinion, Mother should kick out this troublemaker who's a stranger., and ends on Jiang.
Chapter 816, "Don't Take Them Seriously", is the clearest early answer because it turns Mom's situation into a concrete plot event. The setup is Unexpectedly, they didn't cry or fuss;
Chapter 637, "Does President Shang Know That His Own Family Is Already Bankrupt?", is the clearest early answer because it turns Shang Shaojing's situation into a concrete plot event.