The pet bat could make Harry's life more interesting. It could be his companion during lonely times, like when he's in his dormitory and the others are asleep.
The bat might give Harry an edge in some situations. For instance, if there's a task that requires stealth or the ability to fly around and spy, the bat would be very useful. It could also help Harry communicate with other creatures that are more likely to interact with a bat than a human.
The dog could provide Harry with unconditional love and companionship. In the often - lonely world of Hogwarts where he has so many secrets and enemies, the dog would be a constant friend. It could also help him relax, like when he's stressed about exams or Voldemort.
Let's say his pet is a dementor. It would change the whole atmosphere of the story. The characters would constantly be in fear of having their souls sucked out. It could also be used to guard important places. For instance, Voldemort might place it near the entrance of his lair. This would make it extremely difficult for the heroes to approach as they have to deal with this terrifying creature first. Also, it could spread a sense of despair among the wizarding community, making people more vulnerable to Voldemort's control.
The pet might cause trouble for Harry. Imagine it has a mischievous streak and keeps getting into places it shouldn't be, like the Slytherin common room. This would lead to all sorts of awkward and dangerous situations for Harry, forcing him to come up with creative solutions to get out of trouble.
It can also influence new fan creations. Some new fanfiction writers might be inspired by the more controversial 'Harry Potter Insults Fanfiction' to either create their own version of it or to create works that are a reaction against it. For instance, they might write stories that focus on healing the relationships that are damaged in the insults fanfiction.
The 'harry potter wank fanfiction' can be really divisive in the fandom. On one hand, some people who are into more adult - oriented or edgy interpretations might be drawn to it. But on the other hand, for the majority of fans who love the original values of the series like friendship and magic, it can be off - putting. It can also lead to a bit of a rift in the fandom, with some fans distancing themselves from any association with such inappropriate content.
The pet might introduce Harry to new magical creatures or areas. For instance, if it's a cat that loves to explore the Forbidden Forest, it could lead Harry to discover hidden places or meet other magical beings that he wouldn't have encountered otherwise. This could expand his knowledge of the wizarding world and his own powers.
The protective brother can change the plot significantly. For instance, if he's highly skilled in magic, he can prevent Harry from getting into some of the dangerous situations he faces in the original series. He might be able to stop Harry from entering the Triwizard Tournament by interfering with the Goblet of Fire's magic. This would then change the entire course of that year at Hogwarts and Harry's relationship with Cedric Diggory and others.
Well, it depends on the nature of the curse mark. If it's a dark magic - related curse mark, it might attract dark creatures towards Harry. This would put him in constant danger. He would have to be extra vigilant all the time. Maybe he would start to study more about curse marks on his own to find a way to get rid of it, which could lead him to some hidden secrets in the wizarding world that are related to curse marks.
It can also taint the positive image of the 'Harry Potter' fandom. Outsiders might get a wrong impression that the fandom is associated with promoting or at least tolerating such disturbing content, which is not true for the majority of the fans who love the series for its positive values like friendship, courage etc.
It can cause some unrest among the fans. Ravenclaw fans might feel offended or disappointed. It can also create a negative image of the fanfiction community if it becomes too prevalent. Some fans might avoid such fanfictions altogether to protect their love for Ravenclaw and the positive atmosphere of the fandom.