9. Arkham Asylum - Hidden Plans
The announcement of a sequel to the 2009 Batman game in 2011 was partially redundant due to the inclusion of a hidden Easter egg that more or less spelled out the setting of the next game. Behind a false panel in the Warden's office, there lies a secret room with blueprints for a city - a city that in hindsight is very familiar... What was so difficult to find about it was there was absolutely nothing that hinted towards its presence; the wall was the same as every other wall and was not marked with detective vision and additionally the triple use of explosives was not required at any other point of the game. Quite how anyone could ever stumble across the plans is fairly baffling, unless they were actively looking to destroy as much of the environments in-game as possible, and it seems noone was ever playing the game that way, judging by what came next. Eventually, the Eidos production team felt it necessary to directly inform a game site instructions on how to do it: six months after the game's release.