Skin looks like generic fake plastic, almost like a default phong shader, you know?
Bronze is a metal so it has more dynamic highlights, it has more imperfections in how much light hits it, and you can mess with the hues of the color ramp so it looks like metal (realistically speaking green or blue is somewhere there). Piece by Adarias
that did this kinda literally... And two
These aren't really great to work from.
They are okay for being stylized, I can tell what they are, but the shading on most of these is pretty flat, the detail is pretty uniform, too much noise, not enough iconic shapes, etc.
AlcopopStar has probably improved from that point and it's possible they know about some of this now. If not, hey, here's some free C+C.
Work off of the best reference you can. You will progress faster that way.EDIT:
I did mess with the proportions, here they are more realistic. If that's not out of the range of your sprite's goal I do recommend doing this to challenge yourself, because up to now your sprites' proportions have been the same.
Basic shadow ramp to establish value and separate materials
Making a metallic value ramp and applying it to our sprite
Colorizing to look like old bronze (you could add noise here if you want it to look older)
Another one following Gil's advice.
I don't know man. Too yellow and it looks like gold. But this still works IMO.
Darker green might be a gamma error because it looked fine through here.
The whole thing was kinda like making a model kit. Maybe drawing that parallel helps.