First of all, this is a beautiful peace.
The wings are done quite well, and so is the colors and shading.
The eyes seem a little off, but it's a good clean up.
Seems this was done with marker and pens, and it looks very well done with all the shading!
The Tail and Mane though are a bit more orange than normal.
The mail in Derpy's mouth is very clean and the lines are straight. I like the addition of the heart, acting like it could be a love letter.
Once again, Overall, a beautiful and well done MLP:FIM piece.