Um.....the Joker has five fingers on his hand.
I'd stick with convention and give him just four fingers and a thumb
The angle at which the Joker's hand is appearing in shot would mean that his upper arm is far, far too long (his elbow would be just below his waist, by my estimation).
You need to be very clear whether the playing cards are in front of - or behind - Harley's hat. At the moment there's potential for a tangent.
Aside from that, I love the faces - especially Harley's. The smile is awesome.