With the upcoming multiplayer being confirmed in Bioshock 2, not much else is known about this new mode...until now. What we do know is that the multiplayer portion of the game is set before the events of the first game. It is a prequel of sorts and will have you playing characters instrumental in the fall of rapture. Plasmids are involved, so it is rumored that these people are the first plasmid "test subjects."
Gamestop has a promotion,
that was spotted in the 2K forum, where if you preorder you get access to two multiplayer characters. The characters are "Zigo the Fisherman" and "Blanche the Actress." See below for some really small images the forum poster found. These images, while small, look legit. I'll keep an eye out for more news on this.