Some people like it when games feature a "big head" mode. Others find it creepy. I'm in the latter camp. The above video will not be easily dismissed from my nightmares. But hey, if it's your thing then look! Batman: Arkham City has a Big Head mode!
It's not hard to activate if you know the right trick. The Rooster Teeth guys (via Joystiq) run through it in the above video, but I'll explain it for you here. First: you'll need to be playing on either the normal or hard difficulty setting, in a standard game or New Game Plus.
Get into the game and pull out your handy Cryptography Sequencer. Then hold both triggers down while spinning the two analog sticks in circles, toward one another. In other words, the left stick moves clockwise and the right stick moves counter-clockwise.
Do it right and you'll find that all characters -- Batman, Catwoman and their enemies -- suddenly have nightmarishly large heads and hands. I shudder at the thought.