You Can't Scare Me!
According to Muddy Creek legend, a long time ago, there were two neighboring villages: one village was poor and lived in the forest, and the other was more wealthy and well established. The city village hated the forest village and treated the villagers from the forest village poorly. One stormy night, a rainstorm caused the creek in the forest to overflow and flash flood, burying the entire forest village in a mudslide killing all the villagers. Local legend claims that once a year, the townspeople return to form covered in mud and go to find innocent victims to drag back with them into the mud.
In present day, Eddie and his friends heard about the legend, and discovered that Courtney King, a brave girl that was constantly showing them up, believes in their existence. They planned to have Eddie's brother pretend to be a mud monster and scare her. However, the Mud Monsters turned out to be real and scared the kids off.
In the television episode, only one monster is present and Courtney scolds the monster for being so rude. She ended up talking to the monster until the rain let up, drying the monster. After press came and left, the rain restarted, freeing the monster again. It then attacked Eddie and Hat.
In addition to their appearance in You Can't Scare Me! and its accompanying television adaption, the Mud Monsters appear in the books The Knight in Screaming Armor, and Welcome to the Wicked Wax Museum, from the Give Yourself Goosebumps series. One of the Mud Monsters on the cover was featured as one of the monsters in the Monster Mash mini-game in the Goosebumps HorrorLand video game.