Are there more villains lurking within the walls of Arkham Asylum that we've been told about? The Internet Movie Database listing for Batman: Arkham Asylum points in that direction.
The IMDB listing, pointed out to use by Kotakuite Jippon, lists several characters we already know about, including Harley Quinn, Poison Ivy, Bane, and of course - the Joker. What's interesting is the names we've not yet heard dropped in conjunction with the title. Names like Two-Face, Mr. Freeze, the Penquin, Ra's al Ghul, and the Blue Beetle.
While Two-Face, Mr. Freeze and the Penguin were frequent visitors to Arkham, Ra's al Ghul and the Blue Beetle don't seem to fit in the setting. Ra's was briefly a guest of Arkham, but he wasn't exactly himself at the time. The Blue Beetle is a hero, and with Will Friedle listed as his voice, it would indicate the teenage, Jaime Reyes version of the character, who wouldn't have any real connection with the asylum at all.
Perhaps the listings point towards additional content included with the game, such as episodes of the various animated series. Perhaps the listings are completely erroneous. The IMDB isn't exactly known for its pinpoint accuracy, so this should really be taken with a grain of salt. We contacted Warner Bros. regarding the listing, with the company returning the following statement:
Thanks for giving us a call to inquire about the IMDB character listing for Batman: Arkham Asylum. At this time we can only confirm the actors who have been announced for the game.
This of course tells up absolutely nothing, though they did take the opportunity to remind us that Batman: Arkham Asylum would have a huge presence at the San Diego Comic-Con next weekend, where the "Batman: Arkham Asylum" panel will be led by Kevin Conroy and Mark Hamill, with award-winning writer Paul Dini on hand as well. A hint at big announcements, or just a quick plug?