3. Reminding the reader of what happened in previous books in a series.
Smiled grimly.

After a long hiatus, I read the third book of a trilogy (chuckling at this due to your trilogy comment, because it holds true to this series) and the author did not reference past events. I hadn’t read the books in two years and I had no idea what was going on. Couple that with the fact the books weren’t popular enough to Google a quick summary and the fact that the author had a billion similar characters and no idea of how to edit down for simplicity and clarity… I basically had no fucking idea what was going on the entire time.