In 'umbridge abuses harry fanfic', often Umbridge is portrayed as a tyrant. She might verbally abuse Harry, constantly doubting him and his claims about the Dark Lord. For example, she could publicly humiliate him in front of other students, and try to isolate him. This all builds on the canon idea of her as a very unpleasant and unjust character towards Harry in the original story.
One possible consequence could be a great deal of emotional distress for those who created or supported the fanfic. Umbridge's actions might lead to a sense of fear and oppression within the fan community. It could also potentially discourage the creation of more inclusive fan works in the future.
It reflects it by exaggerating the already existing tension between Umbridge and Harry. In the original story, Umbridge was a very strict and unjust authority figure towards Harry. The fanfic just takes it further. For example, the cruel punishments she gives Harry in the books are made even more extreme in the fanfic.
Some in the wizarding world might be appalled by Umbridge's actions. The more liberal - minded wizards and witches would likely support the creators of the fanfic and condemn Umbridge. However, there could also be those who are more conservative and might side with Umbridge, believing that such fanfics are inappropriate.
One possible consequence could be that she gets fired from her position. If Harry manages to expose her actions, the wizarding school or the Ministry of Magic might not tolerate such blatant abuse of power and take disciplinary action against her.
In the context of the original Harry Potter story, it seems quite abnormal as Umbridge is a very unlikable character to Harry. But in the world of fanfic, anything can happen. Fanfic allows for different interpretations and character developments, so while it's not normal in the traditional sense, it's possible within the creative space of fan - created stories.
Another way Harry could respond is with a sense of shock and disbelief at first. Given that Umbridge is supposed to be in a position of authority, Harry might be momentarily stunned that she would go to such lengths. However, his Gryffindor courage would soon kick in, and he would likely start to resist, perhaps by using his magic in creative ways to protect himself or to disarm Umbridge, all while trying to uphold the values of the wizarding world that oppose such cruel and unjust treatment.
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.
Perhaps in the fanfic, Harry teams up with the other students to stage a large - scale protest against Umbridge. Their united front and the chaos it causes might lead to the school board or the Ministry of Magic realizing that she is not fit to be in charge at Hogwarts. Or Harry could use his connections, like his friendship with Sirius or the Order of the Phoenix members. They could dig up some dirt on Umbridge from her past that makes it impossible for her to continue teaching at Hogwarts.
There might be some fanfics with this concept that are written in a non - inappropriate way. However, in the official 'Harry Potter' universe, such a situation of Umbridge spanking Harry is not part of the canon. Some fanfic authors might explore this in a more comical or alternative - universe - type of scenario that doesn't involve any adult or inappropriate content. For example, they could write it as a form of extreme disciplinary action in a very different Hogwarts where the rules are warped, but still keep it suitable for a general audience.