Well, it depends on the specific fanfiction. Some fanfic authors like to play around with the relationships and concepts in the Harry Potter universe. So it's possible that in certain fanfictions, Petunia is Harry's pet. However, in the canon story, Petunia has a very different role as Harry's rather unfriendly aunt who begrudgingly takes him in. But fanfiction allows for all kinds of creative interpretations.
One great Petunia fanfiction could be one where she has a moment of self - realization. Maybe she discovers some of Lily's old magic things and starts to understand the wizarding world better. It could show her in a more sympathetic light, perhaps she even tries to protect Harry in her own way.
In the world of 'Harry Potter' fanfiction, most writers tend to stay within the boundaries of the original story's spirit. The concept of Harry Potter impregnating Petunia is so far - fetched and inappropriate that it is highly unlikely to be a part of any well - regarded fanfiction. Fanfiction usually focuses on exploring relationships that are more in line with the potential of the characters as presented in the original, like friendships, romantic relationships among peers, or the growth of the characters within the magical world.
I seriously doubt there is a legitimate 'Harry Petunia Piss Drink Fanfic'. Fanfic communities generally focus on positive and creative interpretations of the original works. This idea goes against the norms of good taste and the general spirit of fanfiction, which is to expand on the story in a meaningful and respectful way.
One popular theme is the exploration of Petunia's jealousy towards Lily. In fanfiction, this can be delved into deeply, showing how it might have affected her relationship with Harry. For example, some stories might show Petunia struggling with her feelings of envy for Lily's magical abilities and how that spills over into her treatment of Harry.
One common theme is redemption. Often, Petunia is portrayed as having a chance to redeem herself for her past treatment of Harry. For example, she might finally show some love or understanding towards him.
By focusing on their shared past traumas. For example, both have had experiences related to Lily's death in different ways. Harry lost his mother, and Petunia lost her sister. They could start to bond over this common pain and gradually move towards a more positive relationship.
I don't think it's a very common type. Most 'Harry Potter' fanfics tend to focus on the magical adventures, the relationships between the main characters like Harry, Ron and Hermione, or exploring different magical elements in the wizarding world. While there are some that might delve into darker themes, the idea of Petunia abusing Harry isn't as mainstream as other topics in the fanfic community.
Well, it depends on your definition of 'good'. Some might focus on the complex relationship between Petunia and the magical world in the context of Harry Potter, while others might take a more creative or off - beat approach. You really have to dig through different works to find one that suits your taste. There could be some that explore Petunia's character in depth, perhaps showing her envy of the wizarding world in a new light, or creating a scenario where she has a more positive interaction with the magical elements, which could be quite interesting to read.
One possible fanfiction could be about Petunia discovering her latent witch powers later in life. Maybe she stumbles upon an old family heirloom that unlocks her magical abilities. This could lead to a whole new dynamic in her relationship with Harry, as she now understands the world he belongs to on a deeper level.