I know how you're feeling, you have this sudden feeling to create a sprite and then you're thinking
"man, this would be an awesome sidescroller"
But believe me, the animations, monsters and environment, GUI, layout, icons, npcs, spells(if, assuming so) would take a load longer, and until then you will have lost motivation!
(way to destroy it, huh)
According to the sprite, you were possibly playing Maple Story or similar when you suddenly had this idea, but lets move on.
The sprite lacks shading, look at Animefaces (preferably Chibi, in this case)
to see the plasticity, I would also overwork the general shape giving it a more organic form (axis being more S-like)
(It is adviced to look at normal anatomy aswell)
I also agree to the others, 4 tones and having this little gradient is a waste of colors, use them wisely.
Good luck