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New version
Shading looks a bit flat on the skull and upper regions of the body armor. I say maybe flip it vertically / horizontally and see if anything stands out to you.
TBH I almost like the horizontally flipped version of this painting more but I just like the characters looking to the views right.
Concept art wise I have some comments regarding the story you're trying to sell, and how it's expressed through your painting. Don't want to harp on that though if your main focus was shading.
Really cool concepts and the execution is great, kinda feel the shadings a little inconsistent with the light sources and I feel the flame on the second piece should have a bright glow reflected onto the character but still super high-level stuff waiting to see more in the future