You Can't Scare Me!: Goosebumps Classics, Book 17

You Can't Scare Me!: Goosebumps Classics, Book 17 by R.L. Stine

A girl is not scared of anything. She holds bees and other animals that cause other people to scream. Other kids try to find something that would scare her. Everything they try ends up backfiring. Finally after hearing that she believes in monster, they hatch a plan to have some older kids act as "mud monsters" to scare the girl. At night they all gather to watch the girl as they see some mud monsters approach. Then the older kids show up. When everyone realizes they are real mud monsters instead of the actors they all scream in horror. The book is fairly grounded in reality until the very end when it takes the supernatural twist.