One possible theme could be betrayal. If Bill kills Mabel, it could be seen as a huge act of betrayal depending on their relationship in the original source material.
Another theme might be power. Perhaps Bill has a certain power or motive that drives him to kill Mabel, so power dynamics could be at play here. Also, it could be about the loss of innocence, especially if Mabel is portrayed as an innocent character.
Another theme might be the challenges of a new relationship. In a 'bill marries mabel fanfic', they would face various challenges, like dealing with each other's families or friends. And this could be a major theme as they navigate through these difficulties together. For example, if Bill has a different social circle than Mabel, how do they handle the integration? Also, cultural differences if applicable in their fictional setting could be explored.
I'm not sure specifically which 'bill kills mabel fanfic' you're referring to. It could be a fan - created fictional story within a particular fandom where a character named Bill kills a character named Mabel. However, without more context, it's hard to give a detailed account.
One common theme is friendship. Their relationship is often explored in depth, showing how they support each other through different situations.
One common theme is adventure. Since Bill is often associated with strange and otherworldly things, many fanfics might involve Bill and Mabel going on wild adventures together.
One common theme could be the struggle between Mabel's normal self and the influence of Bill. It might show how she tries to break free from his possession.
One common theme is the exploration of the 'opposites attract' concept. Bill is this powerful, otherworldly and often malevolent being, while Mabel is a sweet, innocent and positive girl. Their interactions based on these contrasting natures are often explored. Another theme is the idea of the unexpected. Their relationship is not something that one would expect in the normal Gravity Falls storyline, so fics often play with this element of surprise.
One common theme is friendship. Since they are from different backgrounds in the original story, exploring how they become friends is a popular theme. For example, they might learn to understand and accept each other's differences.
Friendship is a very common theme. Bill and Mabel have a special bond, and fanfictions often explore how they support and care for each other.
Well, in this type of fanfiction, there are numerous possible plot developments. For example, Mabel might discover some hidden power within herself while being kidnapped by Bill. This power could be the key to her escape or to ultimately defeating Bill. Or, Bill could be using Mabel to access a different dimension or unlock some ancient mystery in Gravity Falls. And the Pines family, along with their allies, would then have to race against time to save Mabel and prevent whatever Bill's evil plan is. There could also be a lot of psychological warfare between Bill and Mabel, with Bill trying to break her spirit and Mabel remaining strong and defiant.
One possible theme could be redemption, although this would be highly controversial given his crimes. Another could be exploring his early career before the scandals emerged. But overall, it's a very difficult area to consider themes for, as his actions are so serious.