Some pre-GDC previews have given us a few more facts about Batman: Arkham City, including side missions, the villain Calendar Man, and Batman's new ability to travel around the city by grappling on to low flying helicopters. Where the Batcopter at?
According to Gamespot , Batman will be able to grapple onto the landing struts of passing helicopters and observe the streets of Gotham below using detective vision. From there it'll be possible to spot Riddler trophies and trapped citizens to save.
Civilians will send out distress signals when they run into trouble. These distress signals can be picked up in detective mode, and can trigger optional side missions.
It's also confirmed that the Calendar Man will be in the game. In comic book lore he's a much maligned villain whose obsession with dates leads him to commit themed crimes on public holidays. In Batman: Arkham City he will give you a number of different responses depending on the time you're playing. The preview demo was shown on St. Patrick's day, which caused Calendar man to recant tales of his St. Patrick Day crimes.
1up meanwhile have news of a GDC surprise that has something to do with radio frequencies. "We were shown a hand-painted billboard in the game that provided a clue, and read as follows: Turn on and tune in before someone checks out: 275.00 325.00.” GDC will kick off very soon and we've got a small army there, so we'll keep you updated should they announce the Batusi dance sequence of our dreams.