The elbow height of the arm is a bit too high. It should be a bit further down by the waist.
The horns look a bit dettached from the head.
The tail angle looks a bit off, I can't really put my finger on why. It somehow almost looks attached partially sideways.
Too much identical lineweight in the coloured piece.
Odd ambient lighting effect. The shadows don't look prominent enough. I'd suggest some high-chroma highlights.
The pose looks stiff and somewhat uninteresting.
Keep up the good work!
"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram