Monster Surprise is a magazine story.
Donald and Douglas have fun scaring Thomas by telling him about Loch Ness in Scotland. The next day, Thomas takes a train of materials for the completion of a new theme park attraction. During his last run, he gets stopped in a tunnel because of track maintenance. The twins arrive shortly after, as he's trying to back out. They see a dragon's face sticking out of the tunnel and get scared, and are relieved to find out it's fake, and for the theme park.