The black and white works brilliantly, in the third frame Dash is pretty relaxed and kind of uncaring about what she is saying. It's not really a big deal, she feels. That frame is also a simple outline with a grayscale gradient, and her eyes portray the same emotion.
Twilight on the other hand has the bookshelf background and highlight in her mane, which really feels like there is something a bit more going on with her. Draws my eyes to her a bit, it reminds me of... I have trouble explaining this. I suppose a stage with an actor, where the lights dim and a spotlight goes on the actor. You see everything else, but you should be paying attention to the spotlight.
Twilight overall also just feels very expressive with her slump, and the look in her eye in the last panel.
My only complaint with the actual art is that I didn't know who Dash was until I facepalmed for not looking at her cutie mark. Perhaps an outline of the different colors of her mane would alleviate that issue, but you also wouldn't want to take away from Twilight's spotlight, so I'm not thinking about shading. Perhaps I'm too used to associating a pony with her colors instead of their mane shape and whatnot.
As for Originality, well, you commented on it already . I do like the black and white, again, contrasting with the pastel pony world.
I will start by saying that yes, it is a much used joke, but that doesn't mean it has gotten any less humorous over time, at least for me. I like the style you used here. While I love Lauren's style in the show, art is meant to be creative and original, and yet so many artists seem to judge based off of how exactly you've managed to re-create rather than re-imagine.
The only things that I might make a point on are the lack of eyelashes, which make Dash look a might more unfeminine than you may have wanted(who knows) and how plain her hair looks. If you were to cover their cutie marks and have her and derpy stand next to one another, the only distinguishable feature would be the eyes.
Other than that I think it's great, and very humorous. Dash's expression was great, and Twilight peaking out when she zaps Dash is a cute touch. Overall I think you did a wonderful job.
Confused. WHERE is the resemblance between Twilie and Bella? I mean, both kept to themselves, moved to a new town, and made friends. But, then....what? Bella falls in love, and almost gets killed (multiple times) and then becomes a vampire. Twilie just saves the world over and over again.