The witch is the obvious antagonist. In a horror context, she could be more than just a jealous old woman. She might be a powerful sorceress with dark motives like sacrificing Rapunzel for some evil ritual. Her control over Rapunzel and the tower makes her a menacing figure.
Perhaps it's a dark entity that has invaded the Hundred Acre Wood. This entity could be jealous of Christopher Robin's happiness and decides to turn his world into a horror. It targets him by using his friends and the familiar places against him. So, this unknown dark entity might be the antagonist.
A talking bird could be a new character. It could be Rapunzel's friend in the tower, helping her pass the time and giving her advice on how to escape. Another new character could be a witch's apprentice who feels sorry for Rapunzel and tries to help her.
The main character could be a girl named Rapunzel who is a tech - savvy blogger. Her captor could be a jealous rival in the blogging world who locks her away to stop her from getting more followers. There could also be a prince - like figure who is a hacker and tries to rescue her.
Well, Rapunzel could be a young artist. Instead of a witch, there could be a jealous art dealer who keeps her locked away in a high - rise studio so that she can't sell her art independently. And the prince - like character could be a young curator who discovers her work online and becomes determined to find her. He has to battle through the art dealer's security and false contracts to reach her.
A power - hungry nobleman from a neighboring land could be the kidnapper. He might believe that by having Rapunzel in his possession, he can gain some sort of political advantage or use her as a bargaining chip against her kingdom.
It could be Flynn Rider. Since they have a strong relationship in the original story, it's very likely that he is the father. They are in love and have been through a lot together, so it would make sense for him to be the one.
The antagonist could be the scientist who was trying to stop the invisible man from misusing his power. Maybe he created the invisibility in the first place but didn't want it to be used for bad things.
Perhaps a new character, a dark sorcerer. This sorcerer might be jealous of Sonic's popularity and power. So, he casts a spell on Sonic that makes him act out of character. In this 'dark sonamy story', Amy has to face this sorcerer who is much more powerful than she is, but she's determined to save Sonic no matter what.
Perhaps in the new Rapunzel story, Rapunzel could break free from the tower on her own without waiting for a prince. She might use her long hair not just as a means of escape but as a weapon to fend off any threats in the outside world.
One key element is the isolation of Rapunzel. In a horror version, her being locked in the tower can be made more terrifying. The long hair that was once a symbol of beauty and rescue can become a tool for the horror element, like something that lures people to their doom. Another element could be the figure of the witch who keeps her there, made more menacing with added dark magic and cruel intentions.