Great work with the value studies! The fact that you are looking for the next level even with your skill tells a lot about your future . I recommend for you to study the values of different materials, if you want to go to the next level.
About the mage, nice! A blast from the past The palette looks great and the rendering is nice. The only points that need fixing imho is the anatomy on the spine and the foreshortening on the arms. Also you could make the light source of the staff a warmer or altogether warm light for better contrast, but that's up to you. If you want I can draw a rough sample, but I suggest for you to look over it first.
PS Solid thumbnails, I can't decide which I like best XD