Well, there are fanfictions where the Dursleys are forced to face the wizarding world more directly due to Harry. Maybe they get involved in some magical incidents that make them realize how important Harry is not just to the wizarding world but also to their own family in a strange way. It can be really fascinating to see how they react in these new situations.
In some fanfictions, the Dursleys might be portrayed as having a change of heart. For example, they could start to secretly admire Harry's magical abilities instead of resenting them. This can add an interesting twist to the original story.
One prank could be Harry using magic to make all of Dudley's clothes two sizes too small overnight. Another might be making the Dursleys' living room furniture float whenever they try to sit down. And he could also use magic to make the food on their table turn into slugs when they're about to eat.
One idea could be exploring how the Dursleys react when Harry starts to show signs of magic before he even goes to Hogwarts. Maybe he accidentally makes Dudley float during a family dinner.
In certain fanfictions of this type, Harry could be found by a powerful but reclusive wizard. This wizard decides to mentor Harry in the ways of ancient and lost magics. Harry then uses this knowledge to not only become a very powerful wizard but also to change the wizarding world's view on things like blood purity. He may also go on a journey to find out why the Dursleys abandoned him and in the process, uncover some dark secrets about his family that had been long buried.
One interesting Dursleys fanfiction could be about Dudley's life after learning the truth about the wizarding world. Maybe he starts to have a change of heart and tries to make amends for how he treated Harry over the years.
One possible plotline could be Harry finding a way to break free from the chains and use his magic to confront the Dursleys about their mistreatment. Another could be the Dursleys realizing the error of their ways after chaining Harry up and having a change of heart. Or perhaps there are magical forces at work that lead to a series of adventures while Harry is still chained, like dealing with strange creatures that are attracted to the situation.
In a fanfiction, perhaps the Flight Camp is in trouble and they need the help of someone from the Muggle world, which is where the Dursleys come in. The Dursleys initially resist but then Harry shows them how important it is. And along the way, they learn more about Harry's world and become more accepting. This could be a story of growth for the Dursleys.
In this fanfiction, it might be that Harry is taken from the Dursleys and thrust into a completely different magical world situation. For example, he could be placed in a magical community that has its own unique set of rules and traditions. He may have to learn to adapt quickly, and along the way, he could face challenges that test his character and magical skills. This could lead to him growing in ways he hadn't before, and making connections with characters that were previously only on the periphery of his life.
One possible plotline could be Harry discovering a hidden magical ability that helps him escape. For example, he might find out he can teleport short distances, which he uses to get away from the Dursleys' house when they are being particularly cruel. Another could be that he gets help from an unexpected magical creature that has been secretly observing him all along. Maybe a house - elf that takes pity on him and shows him a secret passage out of the house.
One interesting fanfiction could be about the Dursleys having a change of heart before Harry goes to Hogwarts. Maybe they start to see the magic in him in a different way and struggle with their newfound feelings of protectiveness. It could show a different side of the usually cruel Dursleys.
One popular fanfiction might be about the Dursleys' secret past that somehow ties them to the wizarding world in a more complex way. For example, perhaps there was a wizard in their family line long ago that they've been trying to hide. Another could be a story where the Dursleys have a change of heart much earlier than in the original series and start to embrace Harry's magical nature, leading to all sorts of comical and heartwarming situations as they try to understand the wizarding world. And there could be a fanfiction where the Dursleys are forced to face the consequences of their mistreatment of Harry in a more magical and extreme way, like being haunted by magical apparitions that represent Harry's pain.