Getting better...

I'm really digging Sebastian's wavy hairstyle, but I think that the strands of sticking up hair need to be illustrated in a thinner, curvier way.

I think hair shading is another learning point for you, but I can't really say too much here since I am also a beginner at art. It would help to have different shades of black and streaks of light grey through the hair, though (I've just looked up an image of the original Sebastian, and he typically has these kind of lightning-shaped streaks through his hair, which looks awesome.)

The eyes are the only other point which look off (as Shadowbanes says below), since the difference in size between them is too great. One eye is too large compared to the other, although it's a good attempt at a three-quarter angle, I must say.

Anyway, keep drawing! You sound like you're having a lot of fun with these pieces, which is always nice to see. :)

3.5 / 5