Hiccup and Toothless

Really strong line-art and beautifully shading. You really get a feel for the muscles and bone structure under the characters, which helps add the the realism and professionalism of the image.
I perhaps feel though that shading could be a bit stronger/darker in order to separate the characters from the background. Highlights might have helped achieve this as well as give the characters more definition.
On a side note, Toothless's tail needs to be slightly longer and the bigger, particularly the end tail fins. You also forgot the fins that start at the base of his tail, but this is just me being picky.

Overall clean, delicate image, with a very sweet story behing it. You have captured their relationship perfectly.