Hello! This is my first critique, so I'm sorry if this isn't helpful.
Pro's: The detail in this piece is absolutely beautiful. I love your technique with the eyes, and the way the light shines through the tree is simply beautiful! The clouds in the background are pleasing to the eye, and I love how you included the little nozzle for Fluttershy's floatee's ^3^
Cons: My cons for this piece are the shading on Rainbowdash's hair and part of the pool. I believe you were shading it like that to depict the leaves from the tree getting in the way of the sunlight, but it ended up looking a bit...awkward, as if she has little craters in her mane. I only noticed this while taking a better look at the picture for this critique, though.