Batman: Arkham Knight players have identified a date-related Easter egg in the game which you can see above (spoilers, obviously).
Arkham City featured a Calendar Man achievement which required gamers to play the game on set days of the month over the course of a year but this Easter egg is much easier to find.
All you have to do is change your clock on PC or console to Halloween, October 31st, and some scene will play for you. However, you have completed the Creature of the Night Most Wanted mission and captured Man-Bat for the scenes to activate.
Batman Arkham Knight is still something of a mess on PC, with an interim patch launching in August ahead of a full fix planned for autumn.