It's Knives Chau! (hopefully!) The developer also goes on to state:
"As far as I know, the sixth character will be a downloadable one and will only come out with the DVD release of the movie."
There's also the mention of extra game modes such as a Dodgeball and a Battle Royal. Maybe we'll find out more closer to the DVD release. Until then, read up on the dev's blog for more screens and random info on the game.