I love this piece. The background may be a sore spot for you but it really defines the picture for me. A complicated background would have distracted from the main point of this piece. Which is, of course, Fluttershy and Angel. Fluttershy's "hybrid" form is well drawn and well proportioned. Her expression is calm and happy, a peaceful moment between distractions by other ponies. Just her, the morning air and Angel, not a care to be found. Angel as always looks angry or frustrated. Probably did not want to be woken this early.
I love the calm and peacefulness of the moment. well thought out and well executed!
And now she is a vampire! Best way I could describe this, and your work in general, solid without being heavy, a good mix of colour applied in the right places. You say you could not do anything interesting with the background, but I think you did well with it complementing fluttershy and her dress. Please keep this up!