Interesting use (and mix) of media. I doubt it was your intent, but I can't help but see some Nightmare Before Christmas elements in here, especially with the moon, sky, and bone-pale shade and expression of the mare. Was the seeming-anthro approach intentional? Is this adapting the cover to something else?

Hm... Is she a mermare/mermaid? Or is the boat why one of them is gone by morning? Intriguing!