Here are some pointers.
You have to improve the anatomy, specially his left leg: it looks like it's sticking out of the body, and its upper part is too small. The upper part of Mario's right hand is also too small. His right hand doesn't look good, and his eyes look a bit lifeless. His pose is also kinda akward. Also, try to make your traces smoother, and paint with more regular lines.
On the upper side, his left hand is very nice (hands are hard to draw).
Lastly, I have a question: is he supposed to be jumping?