In Batman: Arkham City, there is apparently a secret big head mode. How is that mode enabled on each platform?
Kotaku describes how to access this easter egg:
You can also watch the Rooster Teeth video (great channel for achievements and easter eggs, by they way!):
On the PC, it's a bit different. You don't seem to need the cryptographic sequencer. The key combination is:
or in WASD:
And here's a video: