Oh god, I haven't done any Critiques for you since I changed my methodology for them. In addition, it wasn't until this critique that I noticed I was using a flawed system of rating originality, so that star rating is lower than my recent critques. I swear, I'm not trying to sound like an asshole.

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Vision: By my understanding, you had three goals with this piece:

1. Draw something cute. As you're fond of pointing out, it's your style.
2. Draw a TwiDash shipping image. It's pretty clear to anyone who looks at your gallery/favorites that it's your favorite 'ship.
3. Invert the "Twilight as Dash's pet" concept that so many people have taken off with.

Keeping that in mind, I have to judge each of those three aspects separately.

1. This image actually doesn't, in my opinion, match the rest of your gallery in terms of "cuteness". That said, I don't see that as an outright negative. You have a far wider range than you give yourself credit for.
   
   That said, this image doesn't quite have much to make up for the lack of cuteness. On a technical basis, it's good, but when it comes to outright intent, I can't see it as holding anything worthy of note.
2. It certainly is TwiDash. Not particularly original, no. But you weren't exactly aiming for something original, so I can't, in good faith, judge that as a negative point.
3. You certainly inverted the concept others have worked with. Again, not particularly innovative or original, but you weren't trying to be "innovative or original", so it would be unfair of me to judge you negatively as a result.

Originality: You've read my critiques before, so you know the drill: It's fanart, so I'm not going to give you full points for originality. That said, it's still kind of original. Plenty of artists leapt to the conclusion, after that episode, that Twilight "secretly" wanted to be Dash's pet. The inverse assumption has (at least, so far as I've seen) remained untouched.

Shipping pictures aren't exactly "original" concepts to draw. But you at least had something to add, rather than making a generic shipping image.

Technique: Your ponies are great as cartoon characters. But as ponies, they're a bit unusual.

You nailed the eyes. The coloration of the iris is beautiful, and the eyebrows, particularly, show a degree of emotion that is impressive. We can tell exactly how Twilight and Rainbow Dash each feel about this situation, merely by looking at their eyes, and, in particular, their eyebrows.

Their poses are solid as well. Twilight and Rainbow Dash's stances are proportionally sound, lending them a feeling of "3-dimensionalness" that a lot of your previous work lacked.

Your anatomy seems a bit flawed, though, considering the source material. Rainbow Dash's wings seem awkwardly placed on her body. Considering their half-erect state, that may be explained away by the inherent awkwardness such a pose would hold, but that does not change that the pose doesn't work well. Twilight's tail seems a bit awkwardly large in proportion to the rest of the image, lacking the depth of the rest of the piece. Her horn looks a bit awkward as well. It seems as though it is (from Twilight's perspective) slightly to the left of her forehead. The point of it also seems a bit too "sharp" for the show's style. I'd suggest rounding it off a bit more.

The last point regarding anatomy I have to make: Your pony-snouts don't look like pony snouts. Twilight's curves too sharply, almost looking like a nose, rather than a snout. This could be stylistic, if done properly, but I don't feel that this was your intent. Similarly, Dash's snout is too short/flat, reminiscent of a dog's snout. Had you given her other doglike qualities, this could be explained as intent, given the subject matter of the piece, but the lack of such qualities suggests that you did not intend for this to happen. Considering how skilled you are when it comes to humanoid noses, I think this is something that, with focus, you can improve on quite easily.

One last point regarding the ponies themselves: You have a beautiful color palette. It's not quite show accurate, but it lends your work a style of its own, and I prefer it this way. Don't change it.

It's pretty clear that you didn't intend for the focus of this piece to be on the background, so I won't bother with much criticism in regard to it. That said, I feel that you should have used a different light source. Credit where it's due: You were consistent. The only seen light source is the sun, in the background, and as a result, all of the shadows are on the side seen by the viewer. The problem, of course, is that this means all of the shadows are on the side seen by the viewer. My suggestion would have been to move the sun to behind the observer, so that the focus of the lighting would be on the side of the ponies that we see.

Impact: I, personally, didn't experience any emotional impact as a result of this piece. That said, I don't feel that it was necessarily your goal to impact the viewer emotionally. In addition, I'm not particularly your intended audience for any such emotional impact, as I'm not particularly interested in the "shipping" aspect of MLP. With that in mind, I'm ignoring this, rating-wise, and giving it a "bye", so to speak.