1. The main characters are told that something they've been searching for (a person, a concept, a place) doesn't exist.
2. An object that has been only loosely mentioned but is important to a character turns out to have a message written in code.
3. An important character turns out to have a hidden dark past.
4. An important character turns out to have a hidden their true personality for the entirety of the story.
5. The main villain of the novel turns out to not be the main baddie after all.
6. A situation arises where a protagonist has no choice but to side with a minor bad guy.
7. The hero finally gets an opportunity for revenge, but it come at the cost of something else.
8. An antagonist unexpectedly does something to help the hero. What is their true motivation?
9. A character turns out to know something they weren't supposed to know.
10. A character dark past finally catches up with them.