One famous malevolent ghost story is 'The Bell Witch'. It's about a witch's spirit that haunted a family in Tennessee. The spirit would cause all sorts of chaos like making strange noises, physically harming family members, and even causing objects to move on their own.
Well, in malevolent Pokémon fanfic, the plot usually revolves around some sort of malevolence. It could be that a trainer has an evil plan involving Pokémon, like using them to take over the Pokémon world. The Pokémon in these fanfics may also have abnormal and more sinister behaviors compared to the normal ones. Maybe a Pikachu that doesn't like electricity but uses dark magic instead.
I'm not sure there are widely known 'malevolent Pokémon fanfic' specific writers in the mainstream sense. However, in the vast world of Pokémon fanfic communities, there might be some who are known for their darker takes. But it's hard to name one off the top of my head as it's a bit of a niche area.
Often, greed is a central theme in malevolent true stories. Greed can drive people to act in extremely malevolent ways, such as embezzling funds from charities or defrauding the elderly out of their life savings. It's a sad reality that these things happen in the real world and they often make for disturbing but true stories.
Not all of them. There could be friendly ghosts in the stories. For instance, a ghost that protects a place or a family. It might be the spirit of a former owner who still cares about the property and its inhabitants. However, there are also likely to be malevolent ones that create fear and chaos.
It depends on the individual stories. Some ghosts might be friendly, like a benevolent spirit that is just lingering around to protect a place or its former loved ones. However, there are probably also malevolent ones that are out to scare or even harm people who cross their paths.
One of the early malevolent ghost stories might be from ancient Japanese folklore. There are tales of vengeful spirits known as onryō. These ghosts were often created by the wrongdoings against a person in their lifetime. They would return to exact revenge, causing harm to those who had wronged them or even to innocent bystanders. For example, the story of Okiku, a maid who was wronged and became an onryō, haunting those around her.