I don't like the dentist, he doesn't give me any candy after the visit. T_T
Anyway! Great great job!
The portrait is complete for what it wants to show! The colours are well chosen, no repetition or weird palettes.
The only thing I want you to look out is his left horn, I don't think it's that big! :0
But I surpass this only mistake, mainly because it's just a sketch.
And for being a scatch, it's nicely made!
By the way, good job! ;)