it doesn't seem natural for sonic to have his mouth running while running.
Umm, do you mean open while running? Or smiling while running?
I'm known for feeling nice some days. Some days.
That sprite looks amazing from a distance, but it's really messy to work with, like the default sprites. Did you do a large image and scale it down by any chance?
Excuse you, but I do this all without even scaling it down. All that detailing you see, I placed it all on my own, pixel by pixel. T'was always how I've done it for all of my SRB2 sprites, and the best part is that this sprite isn't even close to the mess that it was working on Knuckles, because I intentionally kept it more simple than the default sprites are.
Of course, if you think that's too complicated for you, you better start practicing. Spriting was never meant to be easy.
I would hope this gets done soon but r543 told me that he does one to two sprites a day, so who knows how long this will take. BUT, if it is takes longer, the sprites may be of really great quality.