Official Advance - Joe the Echidnafox

So, you want to learn how to shade sprites in the Sonic Advance style? Well, it's not too hard to do, so let's begin shall we?

We'll start by using a Sonic sprite that has had all shading removed.

First, we'll get our palette. Sonic Advance sprites were used for GBA games, which generally have a limit of 16 colors, so our palette will have no more than 16 colors.

To start the shading, we'll start with Sonic's blue fur. At the front, we'll outline it with the second darkest shade of blue, with the darkest being placed where the second shade touches. There is also a small outline around the eye.As we move closer to the back, more of the second shade will be used, and the outline will be the darkest shade, with black being placed in many spots where the darkest shade will touch. Sometimes, the outline will be of the darkest shade while it's next to the lightest shade. It can change like that depending on the amount of shading. Shading is placed depending on the light source, which in this case, above the area in front of the character. So more shading will be in the lower areas toward the back of the sprite.

The rest of the sprite is generally shaded the same way, though smaller areas will not have as much shading, or nearly no shading. Note the eyes have no shading at all.
Well, that's pretty much how to shade in Sonic Advance style, in the best of how to explain it.