Lovely work sugercube, one thing I like is the expressions of each face, and how each face is chaotically blended together. Its as if Nightmare Moon is shifting into different emotional states at the same time.
Everypony just got screwed. Thrice. I haven't seen this particular idea before. I don't mind not having seen it, either.
Impressive job, maker. I always appreciate traditional pony art, and this is certainly a high-quality example. Her armour feels as metallic as can be, the jumble of colours interspersed with the stars of her mane(s) and tail provides for a good background for the monster before us, and the detail on her feathers, faces and eyes is wonderfully precise, particularly for this medium. Masterfully done! Keep on being awesome, maker!