This drawing is just perfect! There are no mistakes.

I like the dragons head and teeth. Those claws are perfect and i like that dragons legs are long and slender.
Chains are very proper. Dragons tail is nicely long and slender.
Drawing looks very realistic and nice. I really like the drawing style and the drawing technique.
Love the dragons pose. Drawings idea is good and it you drew it faultlessly.
Shades are made correctly and the tail is disappearing daintily.
This is amazing artwork!

I dont see anything wrong in that drawing. I would give more stars, if i could.