The biggest reveal in the Global Guardians PBEM Universe was the fact that Stone's mother was a supervillain, and that his father abandoned him at an orphanage in order to hide him from her.
In Lost: Mystery of the Island, a series of four jigsaw puzzles released in 2007, Ottendorf cipher was used on each puzzle's box to hide spoilers and reveal information about the show to the fans.
More often seen is a similar trick where a scene appears to be complete, only for a later episode to reveal that something significant happened right after the apparent end of the scene, or even reveal that the scene itself was manipulatively edited to hide something in the middle of it.