Sammy reveals his nickname for his genius brother Simon, the "serious mutant", early on in the book. It looks like a throwaway line at first, but the Tomato Surprise at the end, including the description of what they look like, reveals that the line was foreshadowing The Reveal at the end.
that this book is actually a Stealth Sequel to Welcome to Camp Nightmare. Which doesn't sound too far-fetched given the "every single character turns out to be aliens" Twist Ending.