The Horror at Chiller House (Goosebumps Horrorland #19)

Jonathan Chiller has called the kids from books #13-18 back to HorrorLand to collect payment. The only way for the kids to get back home is for them to win at a HorrorLand-style scavenger hunt. They each must find a red chest. Inside, the miniature Horror will act as a portal to send them back home.
They'll be competing against Murder the Clown, Chef Belcher, Mondo the Magical, and three other unsavory characters from the previous six books. Little do they know that all six adversaries are actually Chiller in disguise. And Chiller will lie and cheat his way to victory.