Update: Sony has told Eurogamer that Infamous 2: Festival of Blood will be a standalone PSN game.
In other words, you won't need Infamous 2 to play Festival of Blood.
Original story: Sony has announced Infamous 2: Festival of Blood.
It was described by Sony as a "brand new game" that will be available via the PlayStation Store in October (probably around Halloween).
Festival of Blood follows a vampire invasion of New Marais. Infamous 2 hero Cole MacGrath has been bitten, infected. He has one night to find and kill the head vampire.
There are "hours" of new gameplay as well as fresh themes, environments and monsters to encounter.
Sony said Festival of Blood explores the "darker side" of the Infamous 2 universe.