This image was taken from the preview site of Sonic Battle on SonicTeam.com, and was recoloured by Hivebrain. These were the first images of the Character artwork for Sonic Battle. Click the image for a larger version.

But as you can see here, in a later version in a piece of artwork, the style is similar, but has also changed a lot. Sonic has a lor more detail on himself, and it's more like it's only the dark outline which is edge rather than Sonic himself. Also note the eyes have been changed to be one colour, and are now round rather than rectangular. Click the image for a larger version.

Again, this is Shadow ina similar style to the first picture, with the edge enhancements. Click the image for a larger version.

In later images Shadow has been changed to fit the style like the second Sonic, with full coloured, round eyes and much more on model.