In this fanfiction, perhaps Dudley's envy of Harry's magical world finally boiled over into uncontrollable rage. He might have found a way to cross into the wizarding world without anyone knowing. And in a moment of extreme jealousy and anger, Dudley could have used some kind of weapon or spell (maybe through some dark magic loophole) against Harry, which unfortunately led to Harry's death. Fanfiction allows for these extreme and unexpected plot twists.
In this fanfiction scenario, it could be that the writer decided to change the power dynamics completely. Vernon, who is usually just a Muggle bully in the original, might be given some unexpected power or weapon in the fanfic. And Harry, perhaps caught off - guard or having lost his magic temporarily, could be killed by Vernon. It shows how fanfiction can turn the whole story upside down.
One possibility is that the Dursleys, out of their extreme hatred for anything abnormal, actively sought ways to harm Harry. They might have found some dark magic item or spell that they used against him, and without the proper protection or knowledge to counter it, Harry succumbed. In the world of fanfiction, there are many dark and creative ways to make this tragic scenario come to pass. For instance, the Dursleys could have made a deal with some dark forces, trading Harry's life for their own 'normal' life, and those dark forces would use powerful and insidious magic to end Harry's life.
One possible scenario could be that a group of Hogwarts students, while exploring a hidden cave near the Forbidden Forest, accidentally trigger a magical trap. Maybe they were searching for some rare magical ingredient for a potion. The trap could be a spell that causes the cave to start collapsing, like the rocks begin to fall and the entrance gets blocked. They then have to use their magic skills, like levitating the rocks or using the reducto spell to clear a path out.
The 'Harry Potter killed by Dudley' fanfiction could explore themes like the darkness within ordinary people. Dudley was an ordinary Muggle boy, but in this story, he becomes a killer. It also might touch on the idea of the butterfly effect. A small change in Dudley's character or actions led to this huge event - Harry's death. This could make readers think about how small decisions can have big consequences in life, or in this case, in the fictional wizarding world.
Well, if Harry and Dudley became friends, it would drastically change the whole dynamic of the early Harry Potter story. For one, Harry might not have felt so alone at the Dursleys' place. Dudley could have protected Harry from Vernon's wrath. Also, they could have shared secrets about the wizarding world with Dudley being a Muggle. This new friendship might even have led to Dudley developing an understanding and acceptance of the magical world much earlier, and perhaps he could have been an ally to Harry in the fight against Voldemort, instead of a bully.
One way could be to have the Cartoons Ninja be a magical being from a different dimension that has the ability to cross into the Harry Potter universe. Dudley could encounter this ninja first, thinking it's just some new strange thing in his muggle world. But then it turns out the ninja has a connection to Harry's world. Maybe the ninja is on a mission to find a powerful magical item that Harry also needs, and Dudley gets caught in the middle.
One possible plotline could be Dudley getting involved in the wizarding world in some way. Maybe he accidentally discovers a magical object and has to rely on Harry to help him deal with it. This would force them to work together and could lead to a better understanding between them.
Another possibility is at a Hogwarts event. Let's say it's a special ceremony. Harry accidentally bumps into Snape, and instead of the usual scolding, Snape gives him a rather cryptic piece of advice. This first interaction sets the stage for a series of events where they gradually learn more about each other's pasts and motives, leading to a more complex relationship.
There might be some extremely dark and non - canon fanfictions out there with such a disturbing plot. However, this goes against the general spirit of the Harry Potter series. In the official story, Harry is a hero who overcomes great challenges. In a fanfiction with this idea, perhaps it could be due to extreme despair from losing too many loved ones or feeling an overwhelming burden of his destiny that he snaps and takes his own life. But again, this is a very unorthodox and sad take on the character.
A plot twist could be that Dudley has some latent magical ability that is awakened when he is in a life - or - death situation with Piers. This would completely change their relationship with Harry as now Dudley is also part of the magical world in a way.