I don't understand where the light source is on the big guy, it seems to be coming from many different directions depending on the part of the body you're looking at. he's looking pretty monochrome right now, unless that's intentional I'd think of mixing it up and throwing in some colors that aren't dull browns, a little saturation or stronger hue shifting couldn't hurt. he's pretty flat right now, once you decide on a light source try to shade the forms according to it so that he has volume- right now many areas are shaded independently and usually as a gradient or pillowshading.

articuno is nice but some strong highlights here and there couldn't hurt.

duck ain't bad but I think you could use more interesting greys, and it seems to be a bit over dithered. I don't see that the selective-outlining is really helping the piece either. also the head and body seem to respond to two different light sources.