Not bad man, I only have a couple things to say:
The bird looks a bit flat- and I don't mean that it doesn't have any depth, but that the depth is too restricted to localized changes. The wings stick out fine, one leg is behind the other- but the same is true for an origami bird. There's a large area on the bird's torso, up into the underside of the wing, onto the neck and one leg and tail a bit, that has the same average color. I think you paid such close attention to the feather pattern that you lost touch with the fact that that area should be conforming to the body of the bird. I get the impression that you have a piece of glass pressed up against the bird.
You can probably fix that very easily by shading a bit more along the pit of the wing to imply some foreshortening, and defining the musculature of the legs a bit butter under the feathers (which, if you're going for anatomical correctness at all, look like they spring from the body a bit too low down on the tail).
I can't really comment much on the skull guy; too simple and ephemeral a design to find much wrong with it (not that that's a bad things at all, sometimes less is more). The only thing I can say is what you have already- the foreground arm is funny. It's either too short, or you need to make a bend in the arm a bit more obvious because at the moment it's not projecting enough toward us to be that foreshortened (and the shadows don't imply it).
The ninja mummy only has one problem I see: his/her left arm (our right) seems a bit off. By the hand it looks like the elbow is bent toward us a bit, in which case I would suggest shadowing the joint and the base of the forearm to enhance the foreshortening and clear this up.
Aside from that I don't see any glaring issues. Good luck sorting out whatever existential dilemma you've come upon.