Well, Harry could also use his knowledge of magic to play pranks on them that are more sophisticated. For example, he could make it seem like the Dursleys' voices are constantly changing pitch. Every time they speak, they sound like a squeaky mouse or a deep - voiced giant. This would drive them crazy as they wouldn't know how to fix it, and it would be a great revenge for all the times they made Harry's life difficult.
Maybe Harry uses magic to make their house a mess. He could turn Dudley's room into a pigsty or make Aunt Petunia's precious china float and then smash. It's his way of getting back at all the years of mistreatment.
Maybe Ginny did something that Harry thought was a betrayal, like siding with someone against him in a wizarding conflict. So Harry decides to play some harmless pranks on her to get revenge. For example, he might use magic to make her quill write silly things during a class.
One possible plot could be that Harry discovers some deep - seated corruption within the Ministry. He starts by gathering evidence secretly. Then, he uses his skills and the help of his friends to expose the wrongdoings in a very public way, perhaps through a magically - enhanced news broadcast that reaches every wizarding household, causing great embarrassment to the Ministry officials involved.
Perhaps Harry finds out that the Order has made a deal with someone he doesn't trust. In his revenge, he could expose this deal to the wizarding community. He'd use his influence as the Boy Who Lived to make sure the public knows. He might gather evidence and present it in a very public way, like during a big wizarding event. This would not only embarrass the Order but also make them lose the trust of many wizards and witches who previously supported them.
His friends from Hogwarts like Ron and Hermione. They are always by his side and would probably be more than happy to help Harry get revenge on the Dursleys. They might use their magic skills together to create some really interesting revenge scenarios.
Well, perhaps Harry would start by making the Dursleys' house a bit of a chaos. He could make the stairs creak whenever Uncle Vernon is trying to sneak around, or make Aunt Petunia's precious china rattle whenever she is being particularly mean. He might also use magic to make Dudley's new clothes look like old rags in front of his friends, which would be quite embarrassing for him.
In a 'Harry Potter gets revenge on Dumbledore' fanfiction, Harry could find out that Dumbledore knew about certain threats to his life but didn't do enough to protect him. So, Harry decides to get revenge by undermining Dumbledore's influence at Hogwarts. He might start by convincing the other students that Dumbledore isn't as infallible as they thought. He could do this by revealing some of Dumbledore's past mistakes. Then, he could work on getting the school governors to question Dumbledore's leadership, gradually chipping away at his power and status within the wizarding community.
Perhaps Harry uncovers a conspiracy where all his friends, the teachers at Hogwarts, and even the Ministry of Magic were in on a plot to control him. He then decides to take revenge in a very calculated way. He starts by sabotaging the Ministry's operations secretly. He might use his invisibility cloak to move around undetected and cast spells that disrupt their meetings or plans. For his friends, he could play mind games, making them feel guilty about their actions without revealing his true intentions at first.
Well, one possibility could be that the Dursleys suddenly realize Harry's importance and the power he holds. They might see how he could bring them some sort of status or protection in the wizarding world. So, they start to accept him, change their attitude towards him, and perhaps even help him in his magical studies in secret.
In some interpretations, it could be that Harry finally snaps after years of abuse from the Dursleys. Maybe they pushed him too far one day and in a fit of rage, he uses his magic to end their lives. It's a very dark and extreme take on the Harry Potter universe.
Well, maybe Boruto's family or friends are hurt by a powerful enemy. So he decides to train hard and seek revenge. He might travel to different places to learn new jutsu and gather allies along the way.