Awesome piece. Love your drawing and coloring style. One thing though - Twoface's expression conveys less of "got hit in the jaw with a baton" and more of a "making a kissy face for the camera" kind of thing. It's more prominent the smaller the image is. ... Heh... BATon... I'll show myself out.
I can bet it took a lot of time. Seven visible characters in the right composition and movement? That's daring.
...Zsazs's blade! I didn't catch that the first time...
I find also interesting to have Twoface and Nightwing in front and Joker and Batman in background. I think that was the decision that made this quite unique. It suports the feeling of crowded chaotic scene and seems to be more realistic then if it was vice versa - Batman and Joker in front would feel like cool, classic, but unnatural constructed poster. ...Really, you can tell by first look you had to plan.
We've just done a Batman and Bane picture so we didn't want another where Batman was central and we have another with the Joker and Harley Quinn. With Nightwing not having been in any films it's always a bit more of a risk putting him central but the favourites seem to suggest people know him well enough and like the layout.