Well it's time to get on to the crit then:
I picked Serratyr for this exercise since you dislike Palledrig and it's easier to edit than Weechant (heh, very cute). First thing I did, altered the position of the head. The perfectly side on view of the head almost never happens in Pokemon sprites in general less so in leaf green/fire red so I moved it to a more dynamic position, then I altered the shades. Your original body shade went down in a scale of 20s on luminescence and altered saturation and hue little. I lightened it, added more contrast to lum and slightly altered the sat and hue. Respecting your intent I left it as close to the original colours as possible (ironically it's still darker than shiny Charizard). The large white style of eye never has a pure black outline and is usually shaded underneath with dark body shades if at all. Filled in the gap in the bone behind the head and left Marowak's colours alone.
Now for the rest of the body. highlight colours aren't used around the whole body, usually just the head, upper leg and arms depending on their position and shape. I also rounded off the shading to make the light source more obvious. I have no idea of how the arms are meant to be shaped so I left them alone for the most part. I bulked out the bone ribs on the right side since they look as if they're protruding objects and not patterns. The tail doesn't even look attached to his behind and even with my edit it looks awkward. I lightened the lower belly markings to match Marowak's.
Hopefully this shows you steps in which to help improve your work. I had no idea what to do with the arms though.
Thank you. The colors still fit it and the highlights look a bit better. Good job on the head repositioning. I might tweak it a tad bit, but that's just because you don't know exactly what the front is supposed to look like. Thanks for fleshing out the rib bones. That was one thing that kind of bugged me about it. Placing the tail further to the right is more accurate, and lastly, don't worry about the arms. I redid them several times while spriting it to make sure they looked right. Thanks for the trouble.
@ Wichu: As of right now, it is simply a patch that I'm putting together to include the above Pokémon and a few others over the glitches sitting between Celebi and Treecko. Now if you want to use them in the hack you're doing, I would be honored, because they don't have much of a future besides just as additions. I've done their base stats but didn't bother to post them in this thread. They're available by PM if the idea is down with you.