One famous Creepypasta monster story is about Slenderman. He is a tall, faceless figure in a black suit. He is often associated with stalking and abducting children. Another is Jeff the Killer, with his pale skin, cut - in smile and the phrase 'Go to sleep' that he utters while killing his victims.
Sure. 'The Russian Sleep Experiment' is quite terrifying. It tells about a group of test subjects who are kept awake for days in a military experiment, and they gradually turn into something inhumane. Then there's 'Smile Dog'. The picture of a dog with a wide, creepy smile is said to drive people insane if they look at it for too long.
These fanfictions are significant as they expand the lore of the Creepypasta world. They give fans a chance to explore different aspects of Splendorman and Slenderman's characters that may not be fully developed in the original Creepypasta stories.