Alicorn physiology is a fascinating thing. Their manes and tails, in particular, at least those of the most powerful ones, have a tendency to float and billow on their own, as a result of the intense magic present in their bodies. This same magic has, however, very different effects on other, less visible parts of their bodies. Effects that, unfortunately, Twilight had not been made aware of before she had to use such powers. She was not particularly happy about that.

This story is 100% Wintermist's fault.

1908305 on Derpibooru for the cover art, NSFW in case the fact that I didn't link to it directly didn't give it away.