Batman Arkham City GOTY Edition: Exclusive Codes Inside!

Batman: Arkham City - Game of the Year Edition includes several cheat codes and hidden features:

Costume Select Code

To unlock all Batman skins at the start of the game, enter the following code on the Main Menu screen after selecting your save slot:

Left, Left, Down, Down, Left, Left, Right, Up, Up, Down

This will allow you to choose any alternative Batman skin to play with in the main game.

Using the cryptographic sequencer, you can find hidden audio messages:

At 700.00/500.00: A voice repeats numbers that translate to "I WILL RETURN BATMAN"
At 500.00/900.00: Another set of numbers decodes to "YOU WILL PAY FOR WHAT YOU HAVE DONE TO ME"

Complete the game on Normal or Hard difficulty to unlock New Game+ Mode, which allows you to retain all gadgets and XP while increasing difficulty:

99 Skill Points: A cheat to increase skill points to 999 is available, though it requires careful use
Infinite Health: Can be used for most of the game, but should be avoided during certain segments to prevent graphical issues

Remember that using cheats may affect your gameplay experience and potentially cause glitches, so use them at your own discretion.