More than three years after Batman Arkham City was released, players have found a new Easter Egg, in the form of a conversation with Calender Man which seems to hint at the end of the series.
Talking to Calender Man on certain dates, such as St. Patrick's Day, would promt him to have a specific conversation relating to some holiday-themed crime he'd committed. Players either needed to wait for the day in question, or set their clocks forward or back to hear a particular conversation.
The new Easter Egg requires you to set your clock back almost ten years to December 13th, 2004. Arkham developer Rocksteady was founded in December 2004, and Calender Man seems to talk about the studio's early days, as well as what's to come.
He says, "Do you remember my early work? Flawed, but it showed promise." Calendar Man says. "The end of days is coming. I was there at your beginning, and I will be there at your end." Batman Arkham Knight is set for release in June.
You can watch a video of the conversation (skip to the 01:54 mark) and how it was discovered below. Interestingly, it seems Rocksteady itself encouraged players to seek the Easter Egg.