Sketched this on notebook paper, then photographed it and did the rest in GIMP using a (very fiddly) mouse. Saw the alternate cover to the MLP comic with Rainbow Dash in her superhero outfit, and immediately wanted to draw something with her in it.
Though I gotta say, Dashie's outfit is a lot more impractical than Mare do Well's. If her rainbow mane and tail doesn't give her away, she still has her cutie mark exposed. And what's with the atom motif? Ah well, it still looks pretty awesome, and I guess when you're Rainbow Dash, that's really all that matters, right?
Rainbow Dash and Mysterious Mare do Well copyright Hasbro.