How refreshing it is to see some Pokémon artwork that goes beyond the simple comics and outdated poses. It's equally refreshing to see the newer generations share the spotlight!
The line work is nothing short of excellent. The tail, wings, and limbs flow together very well and give it a truly authentic dragon-like presence. It stays true to the cartoon style of Pokémon with just enough added depth and detail to keep it interesting and notable. The saliva dripping off of each mouth is an especially nice touch.
Just as the original colors blend well together, these slightly altered shades also pleasantly contrast. The bright magenta eye adds the right amount of intensity to the Hydreigon's demeanor.
The shading is decent, but could use some more strength, especially around the collar area. The "mane" around it's head could also use some shading adjustments, but such a detail is minute and doesn't distract from the piece as a whole.
The white outline works well against the circular backdrop, but the backdrop seems to contrast a bit much with Hydreigon. The colors on Hydreigon are much smoother, while the pink and purple of the backdrop is very bright and pulls attention away from the subject.
All-in-all, and exceptional piece of fan art. A great showcase of digital drawing skill!