Fluttershy's wraith is as vast as the ocean, always lurking under the surface. These emotions terrify her, and so she is timid to escape situations where she released the beast, but now she has learned to embrace that primal urge and do it well.
...or that could just be what I think, since I'm like that.
I always enjoyed the episodes where fluttershy becomes enraged simply because it implies a lot of hidden anger and possibly resentment that she buries in the back of her subconscious. To stop my random tangent I found this to be quite enjoyable.
Nightmare: *Walks in with a wide, fanged grin, practically resonating with fury and rage* Nightmare at your service, my Lady Fury. Hehe... hehehe... hehehe.... HAHAHAHAHAHAHAHAHAHAHA!!!! LET'S KICK SOME ASS!!!