Batman: Arkham Knight is packed with hidden easter eggs and references to the wider DC Universe. Keep an eye out for subtle nods to other heroes like Superman and Green Arrow, as well as villains who don't appear in the main story, such as Killer Croc or Calendar Man. Explore every nook and cranny of Gotham; you might find hidden messages, iconic locations, or even character cameos. Some easter eggs are triggered by specific actions or at certain points in the story, so replay the game and explore thoroughly.
