I've made my fair share of Pony art since I began watching the show a couple of months back, but undoubtedly my most popular works (according to deviantArt) are my Pony Crossovers.
FlutterDash was the first one I made, and was actually just a random idea in my head. I never planned to continue making these crossovers, but this picture alone gathered more views on my dA than all of my other works combined and I knew I was onto something.
SparkleJack is the most popular upload I've made to dA and probably my personal favorite. Though Twilight isn't even in my personal Top 3 ponies, I like the way this one turned out a lot.
Rarity Pie was actually the second crossover I made, and the image you see here is the second one of this crossover I designed. The original idea was just Rarity's normal appearance, but acting like Pinkie Pie (she was dancing a la Pinkie in 'Party of One'), but it seemed a bit too subtle of a cross.
RainbowShy was actually the answer to FlutterDash, and I only made her due to popular demand (the lineup was originally going to stop after SparkleJack, as all 6 ponies had been accounted for at that point). I like the way she turned out, though I had to put 'roots' for the back of her mane's colors to make them work out right with the entire mane.
Pinkity is my least favorite of all of these. Not because of the crossover idea, but because of the way it looks. It just doesn't have the same quality as the other ones. :/
As for AppleSpark (the only crossover unaccounted for that matches another), I'm not done with her yet, but expect her to be finished not too long from now.
Let me know what you think of all of these, please. I love to hear feedback, both positive and (productively) negative.
