Often, her character is developed through her interactions with other characters. For example, if she meets someone who is afraid of her because of her father, she might start to question her own identity. Or if she befriends someone who accepts her, it can show her softer side. Her character also develops as she discovers more about her father's past and the implications of being his daughter.
One great Bill x Will Cipher fanfic could be 'The Unlikely Bond'. It explores their relationship in a really unique way, showing how they interact in a strange and otherworldly setting. Another one might be 'Bill's Redemption through Will' which delves into the idea of Bill changing for the sake of Will.
One interesting Bill Cipher MLP fanfic could be one where Bill Cipher somehow gets transported into the world of My Little Pony. Maybe he tries to cause chaos among the ponies, but they use their friendship magic to resist his evil plans. Another could be a story where a pony makes a deal with Bill Cipher, not fully understanding the consequences, and then has to find a way to break the deal without endangering Equestria.
One interesting Bill Cipher son fanfic could be 'The Adventures of Bill Cipher's Son'. It might explore the character's unique abilities inherited from Bill. Another could be 'Bill Cipher's Son: A New Threat' where he causes chaos in the Gravity Falls universe in his own way. There could also be a more heart - warming one like 'Bill Cipher's Son: Finding His Place' which shows his journey to fit in or find his purpose.
Well, Bill Cipher is certainly very powerful, but whether he's the absolute strongest is debatable. Different fictional universes have characters with unique and formidable abilities, making it hard to compare them directly.
I think Kakashi would also be a great character to pair with Bill Cipher. Kakashi is very intelligent and experienced. His encounter with Bill Cipher would be full of mind - games as he tries to figure out Bill's motives and powers while also protecting the village from Bill's chaos.
A common theme is the power struggle. Since Bill is an all - powerful being and Mabel is just a girl, there's often a dynamic where Bill tries to use his power over Mabel, but she resists in her own unique way. Another theme is the exploration of the unknown. Bill represents the strange and otherworldly, and Mabel is curious, so they often embark on adventures that involve the unknown in these fanfics.
Well, often there's the theme of isolation. As Bill Cipher's daughter, she may be shunned by others who fear her connection to him. Friendship can also be a theme. She might seek out true friends who accept her for herself. And power is a big one. Whether she inherits some of her father's power or has her own unique abilities, dealing with power and how to use it morally or immorally is a common theme.
First, give the character a strong motivation. For example, if the character is a scientist, their motivation could be to study Bill Cipher's otherworldly powers. This will drive their actions and reactions when interacting with him. Also, give them flaws. Maybe they're overly curious which sometimes gets them into trouble when dealing with Bill.
Their relationship could develop through shared secrets. For example, Mabel discovers a secret about Gravity Falls that only Bill also knows. This creates a bond between them as they keep this knowledge from others.
I'm not entirely sure specifically what that fanfiction is about. It could potentially be about Bill Cipher achieving or obtaining Will Cipher in some way, perhaps in a strange or otherworldly scenario within the context of the Gravity Falls universe. It might involve some sort of power play or a very unique plot device that only fans who have read it would know for sure.