Not only are there new outfits and a new map incoming, but there's even a katana for you to take to a gun fight (which is way more effective than a knife).
Gamers have been embracing Gotham City Impostors since it was recently released. Developer Monolith, as a way of saying "thanks" for all the support, is putting out some free DLC for everyone to enjoy.
The free DLC pack has a little bit of everything. There are outfits for you to dress your impostor with - including Ninja and Luchador themes - a new level called "The 25th Floor" and a bunch of new weapons. The weapons are actually pretty substantial: There's a gas trap that requires you to eat some beans and then fart out a toxic cloud, a pistol that can be modded into a full-auto handgun, and a katana that can also deflect bullets (meaning it can be used to get you up close and personal with an enemy and then cut them down).
The DLC should already be available on XBLA today, but a release date for PC and PS3 has yet to be announced. Hopefully it'll be soon.
Source: Gotham City Impostors