Batman Arkham City: Killer Croc Easter Egg
There is an Easter Egg in Batman Arkham City that can be very easy to miss. This Easter egg must be done right after (SPOILER ALERT) defeating Ra's al Ghul. You can not do it before or later on in the game. Make sure that you DO NOT follow Batman Arkham City's current game objective after defeating Ra's al Ghul or you will miss this Easter Egg!
How to get the Killer Croc Easter Egg in Batman Arkham City
Instead of following the game's current objective after defeating Ra's al Ghul, backtrack the way you entered. You must have Batman navigate though the subway maintenance tunnels. It can get rather confusing here, but look for a gate that you can not enter. One of the subway rooms (bridge room) has a tunnel far above you. Have Batman shoot a rappel to the tunnel to pull him up. The game should notify you that there is a rappel spot above you, so it should not be too hard to locate, assuming you're in the correct room.
Go forward and there will be 3 gates in front of you. The center gate has a small opening at the top. Have Batman throw a remote control bataring through this opening and make it hit the button switch. Note that you can use Batman's detective vision to find the power switch easier.
Once you hit the button with the bataring, Killer Croc will immediately bust through and talk to Batman. This is the Killer Croc Easter Egg cutscene. This does not count towards 100% of Batman Arkkam City (As far to my knowledge and research).
