Well, perhaps the story about the old abandoned house. The descriptions of the dark, dusty rooms and the feeling of being watched make it really scary. It's like you can almost feel the coldness and unease as you read about the protagonist exploring the place.
There are various main characters across the different stories. For example, in 'The Green Ribbon', the girl with the green ribbon is a main character. She is a mysterious figure whose secret about the ribbon is the central mystery of the story.
In 'dark dark room and other scary stories', the tale of the cursed mirror might be quite scary. The thought that looking into a mirror could bring some sort of malevolent force into your life, and that it might show you things that aren't supposed to be seen, is really spooky. It plays on our superstitions about mirrors and the fear of the supernatural.
The story 'In the Dark, Dark Room' itself is quite terrifying. The setting of a dark room where unknown and scary things lurk creates a spooky atmosphere. The description of the place makes you feel as if you are there in that menacing room, waiting for something to jump out at you.
One of the scariest could be the one about the haunted attic. The description of the creaking floorboards and the strange noises coming from the old boxes up there gives a really spooky feeling.
One of the scariest is probably 'The Green Ribbon'. The idea of a girl always wearing a green ribbon around her neck and the mystery behind it is really creepy.
Through its descriptions. The repeated use of 'dark' in the title already gives a sense of gloom. In the stories, the descriptions of the settings, like old, creaky houses or shadowy forests, are very effective.