One interesting storyline could be their origin stories. Maybe they both come from different spooky realms and meet by chance in a haunted house. Their powers could be different yet complementary, like Jimmy Casket having the ability to possess objects and Jonhy Ghost being able to pass through walls. Another could be a story where they team up to face a greater evil, perhaps a powerful dark sorcerer who is trying to take over their haunted world.
A really cool storyline could be that they are on a quest to find a lost artifact in the spirit world. This artifact has the power to either bring peace to the ghostly realm or cause chaos. Along the way, they encounter various other spirits, some friendly and some not so much. They have to solve riddles and overcome obstacles using their wits and powers. Jimmy Casket's devious nature might get them into some trouble at times, but Jonhy Ghost's more cautious approach helps them get out of it. This kind of story would be full of mystery and adventure in the spooky world of ghosts.
Well, Jimmy Casket might be portrayed as a wild card. He's the kind of character who can go from being friendly one moment to being a bit menacing the next. His personality is full of contradictions. He can be very charming when he wants to be, but also has a short temper. Jonhy Ghost is usually depicted as a more stable personality. He's kind - hearted and often tries to help other ghosts in need. He's patient with Jimmy Casket's antics and tries to guide him to be a better ghost in a way, even though it's not always easy.
A possible plot could involve the AllSpark from Transformers having an unexpected connection to the power source of Ghost Rider. Maybe the AllSpark's energy gets corrupted and Ghost Rider has to use his powers to purify it. This would bring together the two universes in a unique way and force both Ghost Rider and the Transformers to work together to save both their worlds.
A really interesting plot could be that Santana was a vampire all along but hid it from Rachel. Then, when Rachel discovers the truth, she has to decide whether she can still love Santana. There could be a lot of internal conflict within Rachel as she grapples with her feelings for Santana and her fear of the vampire world. Also, the vampire lore in the fanfiction could bring in elements like Santana having to drink blood in a way that doesn't terrify Rachel completely.
One of the most intriguing storylines could be where Batman is interviewed about his first encounter with the Joker. It would give a deep insight into his thoughts and how that encounter shaped his view of Gotham's villains. Another interesting plot could be an interview that delves into Batman's relationship with his allies like Robin or Alfred. How he feels about their support and how it impacts his crime - fighting. Also, a storyline where he's interviewed about his no - kill rule and the moral dilemmas he faces when dealing with the worst of Gotham's criminals would be really engaging.
One interesting storyline could be Dark Naruto using the Rinnegan to reshape the ninja world according to his own dark vision. He might start by taking over hidden villages one by one, using the powers of the Rinnegan like the ability to summon powerful creatures or manipulate gravity. Another could be his interaction with other powerful characters. For example, how he would deal with Sasuke, who has his own set of powers and goals. It could lead to epic battles and power struggles.
Maybe a failsafe in a Young Justice fanfic could involve a character being put in a false reality as a safety measure. And the story could revolve around how that character realizes they are in a false world and tries to break free while the rest of the team is also trying to figure out what's wrong with their comrade.
One interesting storyline could be a crossover where the RWBY characters find themselves on the Battleship Yamato. Maybe they have to work together to face a common enemy that threatens both their worlds. For example, a Grimm invasion on the Yamato's world.
One interesting storyline could be Belle trying to break Rumpelstiltskin's curse in a different way. Maybe she uses her intelligence to find a loophole in the magic. Another could be a story where they meet in a different realm and form an alliance before their usual story events.
Another great storyline might revolve around the ancient humans' unique cultures and societies. For example, their art, music, and religious beliefs. Fanfiction could explore how these aspects of their lives were influenced by their environment and the challenges they faced, like dealing with other alien species.
In some fanfictions, the Animalia aspect might involve Animagus forms. Snape could be an Animagus of an animal that has a special connection to Lily. Say he's a deer, which was Lily's Patronus. This would create a very unique and poignant dynamic in the story, as he would be symbolically closer to her in this form.