You asked for a critique, so here is one!

I feel like you got the basic design down very well! Despite it being smaller in size, the proportions are fairly accurate and very few people could say that it doesn't look like the original.
My suggestion is to use the layers in the program to sketch out the body in a larger size (e.g. one layer for sketching, one layer for the outlining, one layer for coloring, etc). That way, you can work more on the little details like the markings on the Rune's wings. Drawing the creature in a larger size lets you play around with shading, highlights, and the brushes within the program.
