I enjoy each of your TwiLuna pieces and this is another great one. But reading the story's description does give this piece a different perspective. Now I need to read it. After ithe prequel one. What I really love about your work is that you give them proper horse necks. It makes all the difference. The sam about the poses that you give them.
You're shading with a solid black, soft round brush again. It's really apparent. Instead of using black to shade, eyedrop the pony's base color, drop the saturation a bit, and just use a darker version of that. It'll improve the aesthetic quality of the image a lot. And you can throw a bit of color into the highlights and shadows too, so it doesn't look like they're sitting under harsh, fluorescent lights.
Sorry if I sound a bit snappy. I got two hours of sleep last night. And I do like your art. But this type of shading looks really amateurish. It gives the picture the same airbrushed look as 90% of all other average fanart out there.