First of all, the coloring is excellent. Plenty of pink, clearly showing your knowledge of Pinkie Pie's color, which is of course pink. I like the movement created by the shading and the way you drew her. Very excellent. The details you added to make her more real and more 3-D are very appreciated. Her boobs helped add to the "movement" I mentioned earlier. It makes it seem as if she's jumping up and down, which was what you wanted, right? If it was then, gimme a hug, you did great!
Now, to criticize the pony Pinkie. No comments there. Only that her element, Laughter, is made obvious with her smile, the sparkle you added, her shiny cheeks, and of course, the light colors you used for the background. You're definitely an excellent artist. Can't wait to see the rest of the Elements of Harmony.
Right now, I must say this is my favorite one. Again, mad I didn't see it before. Nothing says "Element of Laughter" than what appears to be a stifled smile on the pink pony's face. It's innocent, cute, and clutches the heart instantly. Then you have the human Pinkie, who is bringing the joy in big with her super expressive joyful cheer. Love the hair, thick and poofy and just as wild as she is. Stockings just fit...period...love them.
My only qualm with this one is, I'd kind of like to see gleaming sparkly balloons, or confetti in her background just a bit. But YOU are the artist of course, so it's your vision. I still love this regardless! Great job again!