An idea is a story set in a small, isolated town. A journalist arrives to do a story on the town's history but soon discovers that there are some dark secrets being kept. People in the town start acting very strangely towards the journalist, and she realizes that there is a conspiracy to keep the town's real past buried. And she might be in danger if she digs too deep.
One idea could be a story about a young woman who moves into a new apartment. Strange noises start coming from the walls at night. As she investigates, she discovers that the previous tenant was a victim of a serial killer who used to hide his victims in the walls. She then realizes the killer might be back for her.
You could write about a man who inherits an antique mirror from his deceased grandmother. When he hangs it in his bedroom, he notices that there are strange reflections in it at night. The reflection shows a different version of his room, with dark, shadowy figures moving around. As he stares into the mirror more often, he starts to feel a presence trying to reach out from the other side, and he realizes that the mirror might be a portal to a haunted dimension.
You could have a twist where the setting completely changes. Say the story was set in a medieval world, and suddenly there's a portal that transports the characters to a modern-day city. They have to deal with things like cars and cell phones, which would be really strange for them. Also, a character's backstory could be revealed in a way that changes the readers' perception of them. If a character was thought to be a hero all along, but it's revealed that they had a self - serving motive in the past.
One idea could be that the character who seems to be the hero is actually the villain all along. For example, in a story about a detective solving a crime, it turns out that the detective was the one who set up the crime in the first place to gain fame.
One idea could be that the seemingly innocent child character is actually the one causing all the horror. They have some sort of dark power that they are using to torment the adults around them. For example, they make people see their worst nightmares come to life.
Maybe there's a magical object hidden among the beggars' possessions. And as the characters in the fanfiction start to discover its powers, it leads to a race between different groups within the banquet setting. For example, some might want to use it for good, while others for evil.
A woman moves into a new apartment. Strange things start to happen like objects moving on their own. She believes it's a ghost. But it turns out that her ex - boyfriend has installed hidden cameras and is remotely moving things to make her think she's haunted. He's obsessed with her and wants to drive her crazy. This adds a more human - made horror element rather than the supernatural at first glance.
One idea could be to rewrite the main characters' first meeting. Maybe they meet in a completely different setting, like a magical forest instead of a bustling city. This would change the initial dynamic between them.
You could explore a 'what - if' scenario in the 'a twist of fate fanfiction'. What if the main event that set the story in motion didn't happen? For instance, if in the original story a character's death led to a war, in the fanfiction, that character survives and the story takes a completely different turn towards peace and cooperation. Also, you can play with different time periods. Transport the characters to a modern - day setting or a far - flung future.