I can't say much for your black and white work since I don't know the characters well and can't say whether any anatomical mistakes are in fact part of the general style. I do like Shino a lot though, he's cleaner than your other works. These would translate well into vector art but sadly you're having trouble with GIMP. The only possible thing I can see wrong with your Shiftry is your coloured pencils and you can't really help that. It's uniquely posed and has quite a bit of personality. ;p
Your pixel work is something I can critique though with certainty. Two outstanding things that need to be improved are general lineart and colour choice. I can understand that it's hard to pack everything in a small space but if you're unable to place hard black outlines for something such as hands in an area to suit the size of the sprite you should instead use a combination of shading and half outlined shapes to give the impression of the limb or object. Look at official sprites such as Squirtle to get an idea of what I mean. As for your colours they tend to be rather boring linear colour ramps with little change between hue or saturation and it's difficult to distinguish between most of the shades. Mess with the colours a bit and i'm sure you'll find something better.
Feel free to disregard this if you're not particularly interested in improving your work. If you want to go further or don't understand any of the points I made above I can edit one of your sprites with your permission to make it clearer.
~Your friendly neighborhood pixel artist.