Dumbledore's reaction would be very interesting. He is always full of wisdom. He might see this as an opportunity for Harry to learn something important. He could be secretly guiding Harry through this situation, while publicly trying to keep the peace at the school. Pettigrew himself would be very nervous. He knows he is not welcome, but he might also see this as a chance to redeem himself, or at least pretend to, in order to survive in this hostile environment.
The teachers would likely be very cautious. Professor McGonagall might be extremely strict and keep a close eye on Pettigrew. She would be worried about the safety of the students. Ron would probably be very angry at Harry at first. He has a strong hatred for Pettigrew because of what he did to his family. Hermione, on the other hand, would be more rational. She would try to analyze the situation and see if there is any benefit to Pettigrew being back at school.
Hermione would likely be shocked and disappointed. She is a stickler for the rules and the gun would be a blatant violation. Ron might be initially curious but then realize the seriousness of it. Dumbledore would be very concerned and try to understand Harry's motives. Snape would probably be quick to condemn Harry and use it as an excuse to give him detention.
Well, it could drastically change things. For one, Pettigrew's knowledge of Voldemort's plans would be a huge factor. Harry might use Pettigrew to expose more about Voldemort's return, which could lead to a quicker response from the wizarding world. Also, it could change Harry's relationship with Sirius, as Pettigrew was the key in Sirius' false imprisonment.
Harry might face a lot of criticism. The wizarding community might think he's being naive by bringing back Pettigrew. There's also the risk that Pettigrew could double - cross him. After all, Pettigrew has a history of betraying those who trust him. This could put Harry in a very difficult situation, especially if Pettigrew lies about Harry or tries to frame him for something.
The characters' reactions would be diverse. Snape would likely be very critical and use it as another reason to dislike Harry. He might see it as a sign of Harry's lack of respect for the wizarding world's traditions. The other students would be a mix of those who are fascinated by this strange Muggle object and those who are worried about its potential for harm. Hagrid would be confused, not really understanding what a gun is but knowing it doesn't seem right in Hogwarts. Overall, it would create a stir among the Hogwarts community and lead to a lot of discussions and speculations.
The Weasley family would also be greatly affected. Mrs. Weasley would surely mourn Harry as one of her own. Ginny, who had feelings for Harry, would be heartbroken. She might become more fierce in her pursuit of justice in the wizarding world. And the other students at Hogwarts, like Neville, would be inspired by Harry's sacrifice to step up and be braver in the face of danger.
Dumbledore would probably be very calm and have a long - term plan. He might use this as an opportunity to teach Harry something new or guide him in a different direction. Some of the teachers at Hogwarts might be worried about how this will affect Harry's performance in class and his safety at school.
One possible plot twist could be that Pettigrew reveals some long - hidden secrets about the wizarding world. For example, he might know about a powerful magic item that was lost years ago and its location is somehow related to Hogwarts. This could lead Harry and his friends on a new adventure within the school grounds.
Ron might laugh out loud at first. He has a good sense of humor and would find the whole situation hilarious. But then he would also be a bit worried about Harry's dignity. Ginny, on the other hand, would probably blush and giggle. She has a bit of a crush on Harry and seeing him in such an adorable yet silly state would be both endearing and embarrassing for her.
Often, Harry catches Pettigrew by using his invisibility cloak. He sneaks up on Pettigrew and then uses a stunning spell. It's a simple yet effective method that is often used in fanfictions as it plays on Harry's resourcefulness.
Hermione would likely be devastated. She might go into a deep state of mourning, but also use her intelligence to try and figure out what led to Harry's death. Ron would be angry and heartbroken at the same time. He'd probably want to seek revenge if there was someone or something responsible.