Koopalings Custom rpg sprite

[Vipershark]

Anatomy issues aside,
First off, you've got waaaaaaaaaaaaaaaaaaaaaaay too many colors on this sprite.
I can count 18 different colors in use here, and for a sprite as small as this, that's like... probably more than twice what you need.

You can optimize your color usage better by sharing colors between the face/stomach areas and the arm/leg areas since the colors are so similar.
You can also combine the blue of the hair and shell with the green of the head because the green is in such a small area that it isn't very visible anyway.

In addition, there's banding and pillow shading everywhere which you need to get rid of, and your sprite needs a whole lot more contrast as well as some hue shifting.