Very nice work. I imagine this as a symbol of when Nightmare moon was defeated. Luna has her design that means less magical power and she has smaller wings than Nightmare Moon, but she is on top. So she is winning her inner fight.
Nightmare Moon doesn't look evil in this picture. You know, darkness isn't always about evil. It's also about rest and quietness and the time you have to spend with yourself. I always feel this gets a little left out of stories.