The Behemoth has made two Limited Edition characters available to release from BattleBlock Theater prison, Toast and Rose are currently available in the full version of the Xbox Live Arcade title.
To unlock Toast you will need to complete the newest Solo and Co-Op Furbottom’s Features (FF) which you can see at the bottom of http://www.battleblocktheater.com
To unlock Rose you simply need to log in to the full version of BattleBlock Theater before Thursday 16th May.
These characters are available for a limited time before they get locked up again. Will they be seen again? Only The Behemoth knows.