Perhaps Dudley finally stands up to his father's cruel treatment of Harry. Maybe he realizes that Vernon's behavior towards Harry is wrong and uses his own physical strength or some clever ruse to get Harry out of a difficult situation Vernon has put him in.
Vernon is likely a character within the Psychonauts universe. In the context of the Vernon Ghost Story, he's probably the central figure who has some sort of encounter or relationship with the ghosts.
Vernon could be anyone. Maybe he's an old man in the neighborhood who loves to share spooky tales from his youth. Or perhaps he's a young person who had a strange encounter and turned it into a ghost story. Without more context, it's hard to say exactly who he is.
In this fanfiction, Dudley would surely interact with the Hogwarts professors. Professors like McGonagall would be strict with him, making sure he follows the rules. He might also cross paths with Draco Malfoy. Given Malfoy's attitude towards Muggle - borns, there could be some conflict there. And let's not forget the other students in his house. They would play a big role in his Hogwarts experience, either befriending or ostracizing him.
Petunia could be a great addition. Her relationship with both Harry and Vernon adds a lot of complexity. She could be the mediator or the one causing more trouble between them, depending on the plot.
In the fanfiction, Ginny could be developed by exploring her magical abilities further in relation to Dudley. For example, she could use her magic to show Dudley the beauty of the wizarding world, which in turn makes her more confident in her own identity. Dudley's character can be developed by having him face his own insecurities. He realizes that Ginny is different from what he thought wizards were like, and this makes him question his own upbringing and beliefs.
In some Dudley Protects Harry fanfictions, Dudley's character development often starts with a significant event. For example, he might witness the true danger Harry is in from the wizarding world. This makes him realize that his previous bullying was petty. He then begins to feel a sense of responsibility towards Harry. He may start to learn about the wizarding world to better protect Harry, gradually changing from a bully to a protector. This transformation can also be influenced by his own growth in understanding family and loyalty, as he finally sees Harry as more than just the 'freak' he once thought him to be.
Well, perhaps Dudley uses his street - smart knowledge. He might teach Harry some rough - and - tumble moves he's learned from his own scuffles in the neighborhood. For example, showing Harry how to dodge a punch quickly.