So really quick before I get into further details, the black image of Fluttershy was NOT my creation. I mostly replicated this decal on Etsy: [link]
I couldn't find a vector of it anywhere, though, so I just made one myself, via pen tool in Photoshop. After that, I made that the top layer and then I made approximately 30 something layers for the paint strokes, which for that, I used a bunch of random custom brushes that simulated brush strokes. Of course, I had to use Fluttershy's color scheme (eyes/coat/mane) just to make it all her's ;d. This is kinda a basic picture, in that sense, but I still had fun making it!
If anyone wants me to do the other mane 6 ponies, I'll see If I can try it again for them c: . No promises, though.