Hello! I really love this piece and rendering especially!
I think that pushing your values a little bit will help your characters to pop out more, because right now they're kinda blend in with the background. Also i don't understand this really bright rim light on the chest of the wolverine. I don't see any light sources that can give this light.
Here's what i meant: i did a few rough brush strokes with soft brush and i think that it reads better know. Of course it is a overkill but i hope it makes some sense:)