Impressive perspective work and the use of subtle gradients for the shading goes well with the style. I feel that Mario's moustache could have done with more detail, maybe a slight texture or gradient.
Other small details; The star on top of the building looks very flat and the clouds have too much of a brush stroke style to fit the cartoony feel of the figure.
I rather like this piece. I just feel it should have had more time spent on the background to bring it to the standard of the figure.