The Weasley family would have different responses. Mrs. Weasley would be motherly and concerned about this strange new person. Fred and George would see her as a source of new ideas for their pranks and inventions. Ginny would look up to her as a strong female figure, much like she does with Hermione. And all of them together would gradually get used to having Powergirl around, and they would all grow from the experience of interacting with someone from a completely different world.
Another plot could be that Voldemort discovers Powergirl's existence and sees her as a threat. He tries to manipulate the wizarding world against her. But Harry and his friends believe in her and together they work to expose Voldemort's lies and also learn from Powergirl about different ways of fighting evil. Powergirl could introduce new concepts of justice and heroism to the wizarding world.
One idea could be that Powergirl somehow gets transported into the Harry Potter universe. She could use her super strength and flight abilities to help the students at Hogwarts during a time of great danger, like when Voldemort is on the rise. Maybe she teams up with Harry, Hermione, and Ron to fight the Death Eaters in a unique way that combines magic and her superpowers.
Hermione, on the other hand, would likely have a more critical view. She'd analyze the fanfictions for their accuracy in terms of magic lore and Hogwarts traditions. If there were any inaccuracies, she'd be quite perturbed. However, she might also appreciate the creativity that goes into some of the well - written ones that add new dimensions to their magical world.
Powergirl's super strength could be integrated as a form of magic - perhaps she was born with a unique type of magic that gives her physical power far beyond normal wizards. Her flight could be seen as a charm that she has mastered in a different way than traditional broom flying. For example, she could use her flight to quickly reach places in Hogwarts or during battles that are otherwise difficult to access.
Hermione would be extremely curious. She would immediately start researching it, trying to figure out its mechanics and where it came from. She might even try to find a way to improve it or adapt it to the wizarding world's technology.
Dumbledore would likely be very accepting of Stitch. He has a great understanding of all kinds of creatures and beings. He would see Stitch's potential for good and might even try to find a place for him at Hogwarts. Snape, however, would be more skeptical. He would keep a close eye on Stitch, worried that he might disrupt the order of the school or cause harm to the students. The Weasley twins would probably find Stitch hilarious and would want to play pranks with him or use his unique abilities for their own mischievous plans.
Draco Malfoy would probably be outraged at first if he read fanfiction that showed him in a positive light towards Harry and his friends. He's so used to being on the opposite side, but then he might secretly be a bit flattered by some of the more complex characterizations of him.
In a fanfiction, the students at Hogwarts would be really intrigued by Hawkeye. They've grown up in a world of magic, and Hawkeye would represent a different kind of power. Neville might look up to Hawkeye as someone who uses their own skills to fight, without relying on magic. Ginny would probably be eager to team up with Hawkeye in any battles or adventures, seeing his potential as an ally in the fight against evil.
Hermione would probably be very curious about Darkseid at first. She'd try to research him in the Hogwarts library, looking for any clues about his powers and weaknesses. But once she realizes the danger he poses, she'd be quick to come up with strategies to fight him.
Some characters might be excited. They could see him as a new source of knowledge and magic.