This could happen if the fanfiction is exploring a very dark and twisted version of the story. For example, Bill might have used his otherworldly powers to merge his essence with Dipper in some way. It could also be part of a plot where an author is trying to show the extreme lengths of Bill's evil and his ability to corrupt even the most innocent, like Dipper. The pregnancy then becomes a symbol of the violation of Dipper's normal state and the chaos that Bill can bring.
This type of fanfic could be a way for the writer to experiment with character development and relationship dynamics. However, it also might be controversial as it goes against the normal expectations of the show's canon. But that's the beauty of fanfiction - it allows for all kinds of wild ideas. The pregnancy could be used as a plot device to explore emotions like fear, excitement, and responsibility from Dipper's perspective.
One big challenge would be the social stigma. In the normal world of the story, such a situation is completely unheard of and would likely be met with shock and disgust from others.
Well, Dipper might start causing chaos just like Bill. He could use his new powers to play pranks on Mabel, like turning her sweaters into strange, living creatures. Or he could use the power of mind - reading to know what everyone in Gravity Falls is thinking, which would lead to some really awkward and funny situations.
One might expect a lot of drama. Since Bill is a rather chaotic and powerful character, his child would likely bring a whole new level of trouble or potential. Dipper, on the other hand, is a more relatable and 'human' character, so her pregnancy could show her growth and how she copes with this unexpected situation.
Well, in fanfiction, anything can happen. Since it's not bound by the strict canon of the Twilight series. It could be that the writer decided to create a completely different timeline or scenario where Carlisle and Bella have a relationship that leads to her pregnancy. It might involve some kind of genetic manipulation or a special power that allows for this unorthodox union to result in a pregnancy.
In a 'Dipper Gets Bill's Power' fanfiction, Dipper might first struggle to control the power. He could accidentally cause chaos in Gravity Falls, like making objects float uncontrollably or distort the space - time continuum a bit. Maybe he'd start seeing the world from Bill's strange, other - dimensional perspective.
Dipper might become more confident, almost to the point of arrogance at first. After all, he now has a great deal of power at his fingertips. But deep down, he'd still be the same curious and somewhat nerdy Dipper, just with a new - found sense of self - importance.
Well, perhaps it's a story where Dipper gets caught up in Bill's gang's evil plans. They might try to manipulate him into doing their bidding, but Dipper uses his wits to outsmart them. The plot could involve Dipper having to navigate through a series of dangerous situations created by Bill's gang, all while trying to protect his friends and the town he loves.
One way this could happen in fanfiction is if there was some form of time - travel involved. Maybe Hermione traveled back in time and ended up in a situation where she and Severus had a relationship that led to her pregnancy. Another possibility is that a magical artifact forced them into a situation where they had to be together closely, and feelings developed over time, resulting in a pregnancy. Fanfiction writers love to take unexpected turns with characters' relationships.
Often, in 'Bill and Dipper pregnant fanfiction', you'll find themes related to responsibility. Since having a baby is a huge responsibility, the stories might show how Bill and Dipper grow as characters while facing this new situation. There could also be themes of acceptance, both from themselves and from the people around them in the fictional world. Some stories may also touch on the theme of sacrifice, as they might need to give up certain things for the sake of the pregnancy and the future of the baby.