Who the heck is Surprise?
I've learned about as much as one can from fan art. She is either some form of personality inside of Pinkie that personifies itself as a pegasus, or just a completely different pony that happens to be a recolored Pinkie. I can't tell.
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2144439 That helps a lot. Thank you.
2144447 The most common joke about her is that its Pinkie when she goes Super Sayian.
2144459 wait, so that meant originally, the animal caretaker was going to be the Earthpony while the party pony would be the pegasus? Wow, now I can't stop imagining what that would've be like.
2144800 Hence Fluttershy's fear of heights.
2144895 BUM BUM BUUUMMMM!!!