The upcoming game Gotham City Impostors seems to be all about what happens when the Bat is away. Tons of Joker and Batman wannabes come out and run amok through town. Those wanting to join the ranks can apply to be in the limited closed beta coming in September for the PC. Just go here, complete the sign-up form, sit back and wait to see if you’re selected.
As near as we can tell the beta seems to be open to US residents only.
Source: Gotham City Impostors website via Joystiq
