Well, first of all, the settings are very different in Inkheart and Fablehaven. Combining the two settings in a way that makes sense can be really hard. For example, the way magic works in Fablehaven is different from Inkheart. Also, the fans of each series have certain expectations. If you deviate too much from what they expect, they might not like your fanfic. You have to find a balance between creativity and staying true to the source material. And let's not forget about pacing. Since it's a crossover, you need to make sure the story doesn't feel rushed or too slow when introducing elements from both series.
The biggest challenge might be the tone. Inkheart has a certain tone that is different from Fablehaven. Inkheart has a more, in some ways, literary feel, while Fablehaven is more of a fast - paced adventure. When writing a crossover fanfic, you have to find a tone that can accommodate both. Also, the lore of both series is extensive. You need to make sure you understand all the details so that you can blend them together without making mistakes. This requires a lot of research and careful thought.
There are some. I've seen a few on Wattpad. The thing is, the quality can vary a lot. Some are really well - written, with the author managing to blend the magic systems from both Inkheart and Fablehaven seamlessly. Others might not be as good, but it's still worth looking through to find those hidden gems.
Perhaps there could be a situation where the magic in both Inkheart and Fablehaven is being drained by an unknown force. The characters from both worlds realize they need to find the source and stop it. Mo and Kendra could be the leaders in this quest. They start exploring different areas of both worlds, with the help of Dustfinger's knowledge of Inkheart's magic and Seth's familiarity with Fablehaven. Along the way, they discover that the two worlds are more connected than they thought, and there are ancient spells and artifacts that can help them. They face many challenges, like dangerous magical creatures and traps, but they keep going because the survival of both worlds depends on it.
I think Mo from Inkheart and Kendra from Fablehaven would be an interesting pair. Mo has a lot of knowledge about books and magic in Inkheart, and Kendra has her own experience with the magical world of Fablehaven. They could share their knowledge and learn from each other. Mo could teach Kendra about the power of words in magic, while Kendra could show Mo the unique magical creatures and places in Fablehaven.
One challenge is character development. Jafar is traditionally seen as a villain, so making his relationship with Jasmine believable while still maintaining his essence can be tough. For example, you need to find a way to show his transformation in a way that doesn't seem forced.
One challenge is getting their personalities right. Ahsoka is a Jedi with strong moral principles, while Ventress is a former Sith assassin. Balancing their different outlooks can be tricky.
Character development can be a struggle. Since we already know a lot about Light and Misa from the original work, it's difficult to add new layers to their characters in a believable way. Also, the moral ambiguity of their actions in the original story can be a challenge to handle in a fanfic. You have to decide how to portray their actions, whether to condemn or justify them, which can be tricky.
The existing relationships in the Dragon Ball series can be a hurdle. Goku is married to Chi - Chi, and Bulma is with Vegeta. So, the writer has to find a way to make the Goku x Bulma relationship believable without completely disregarding the established pairings.
One challenge is the complex and often dark nature of their relationship. Thanos is a villain who has done terrible things, including to Gamora herself. So, it's difficult to make their relationship believable in a positive or even a nuanced way.
In 'x over crossover fanfic', there's the challenge of dealing with different fan bases. The fans of the 'x' element might have certain expectations, and the fans of the other part of the crossover have their own. You have to try and please both groups without sacrificing the integrity of the story. And then there's the research aspect. If 'x' is from a complex world like a historical drama and the crossover is with a science - fiction world, you need to do a lot of research to make the combination believable.
When writing a Hal x Barry fanfic, there are several challenges. Firstly, their power sets are quite distinct. Hal's power comes from his ring which gives him a wide range of abilities based on his willpower and creativity, while Barry's speed gives him a different set of advantages like time - dilation and super - fast thinking. This means you need to be careful when writing scenes where they use their powers together. Secondly, their fan bases have different expectations. Hal fans might expect a certain level of Green Lantern lore, and Barry fans might expect the same for the Flash. So, you need to find a balance to satisfy both. Thirdly, coming up with an original story that hasn't been done before in the many existing fanfics can be tough.