You did very well on this character, Pinkiedash.
You cut the character's outlines very sharp, which gives the character it's evil look. Along with the color scheme, those are the two main elements of why I describe this being by the term, "evil."
What stands out to me the most is the color hues of the eyes.
The Changling's body is naturally dark; along with the brighter hues of the eyes, how the eye-color blends in with the dark shading of the coat, and how the eyes stand out in unison with the blending, makes the eyes a defined highlight to the Changling's appeal and characterization.
(Not blending by painting theory, blending by personality/ emotional theory.)
The wings are the second highlight I see.
When I look at the wings, I can imagine how they must feel so light, how they're so thin you can see your hand right through them, and how they might have a decrepit texture to them because of the hardships you face as the creature that you are.
It almost makes me feel pity for the Changling kind, they probably live like ants under a tree-stump...
The beetle-like shell on the creature's back gives the thought that the Changling body would feel more like it would be an exo-skeletal armor, other than a soft pony hide.
The last thing I'm gonna critique on your drawing is the jutted tooth.
I think it ties the whole personality of the Changling together.
It mixes with the look of the eyes, the sharp outlines of the body, and the coat to make even the youngest of children point at the screen, and say, "That pony is a bad guy!"
Overall it's a fantastic piece!
Personal rating is a good 4.5 out of 5.
I give 4*s on the vision, because of how the colors tie in to the personality of the character.
3.5*s for the originality. because even though it's YOUR piece, it's still the character from the show.
5*s for technique, for obvious reasons.
and 4*s for impact, which me personally is centered around the eyes.