... a unicorn! What else? They're one of the most famous, most unique, most romanticized, most beautiful, most all-around special creatures in all of myth and legend. Sure, it would be fun to experience the strength of a cyclops, the strangeness of a chimera, the longevity of an ent, or the raw power of a dragon. But given the supposed opportunity to be any mythical creature you name, "unicorn" seems like the obvious choice. A tiny white strip spills out of a what looks like a receipt outlet.
WISH GRANTED. A BIG CHANGE IS COMING TO YOUR LIFE VERY SOON. HAVE FUN!
The cheeky piece of paper that printed out of the wish machine makes you so mad that you actually start to laugh. This "wish machine" is basically a very large, inedible fortune cookie, one that just used your pocket-change to give you a dull, generic message with no connection to your wish. What a ridiculously silly device. You feel silly for being taken in by one of these made-up practical jokes yet again. Oh well, perhaps it was worth it to try. After all, these silly superstitions never work, but what if one of them did?
So it is with a heavy heart that you walk back out the way you came and start making your way to one of the more serious stops you have to make: the grocery store. It's a long walk, but hopefully it will still be open by the time you get there. You try not to make eye contact with anyone: you know they didn't see you, but you still have this deep dark fear that someone is going to randomly call you out for wishing to be a unicorn. You don't really want to admit to yourself or anyone else that you believed in the wish machine as much as you did.
You're two or three blocks away from the magic shop, trying to focus on your shopping list, still plodding through the summer heat toward the grocer, when something goes wrong. Your insides feel funny, like they're sliding around and reshaping. You hear weird groans and gurgles coming from inside you, and you suddenly have the largest belly ache of your life. Then your bones start popping, and you start to get larger. You start to notice your extra height when you find yourself eye level with the pedestrian traffic light that is normally several feet above your head. Your midriff and lower legs are bare because your clothes aren't long enough to keep them covered, and your clothes are so tight you feel like you're about to suffocate. A fellow street walker notices your in distress and pulls out her cell phone to call the emergency number; unfortunately, something weird happens to her phone as it suddenly loses service and then the battery goes dead. Your vision changes, and you start to see a strange aura around you and a similar light coming from several blocks away near the magic shop. Is that what magic looks like? What else could be changing you so much in so short a time?
All at once, your clothes burst, and people are left shocked and dismayed that a person is naked in front of them. You grab the tatters and run away, trying to find the most secluded possible place that you can. Unfortunately, that's going to be really hard in a big town like this. You pass by a cop who chases after you blowing his whistle, but you've already noticed that you can now run way faster than you used to! Your lungs are churning like pistons, pulling in large breaths of air through your expanding mouth and nostrils. At first, you wondered if your sudden deformation and nudity were some kind of supernatural punishment for not appreciating your human body enough, but now you're starting to wonder if your newfound strength and speed are a reward for your perennial openness to the possibility of magic. Even if you aren't turning into a unicorn, being a superhuman giant could be cool.
Before too much longer, you've made it to the 23rd Street Bridge, which you hop down from and try to hide yourself under. There's basically just a bunch of trash down here and a highly polluted stream running under it close to your position. This is a pretty dangerous criminal hangout at night, but mostly deserted during the day. Now maybe you can finally get a chance to look over and appreciate your new body. One thing that gets your attention pretty quickly is that you now have long hairs dangling out from the underside of your hands. You wonder how long it took those to grow in? You can see and feel them waving in the breeze, even more noticeably when you swing your arms around a bit. The light breeze also helps you discover that your hair is a lot longer in some places and a lot shorter in others, waving proudly from your head all the way down your neck and shoulders like a, like a--
"A mane?!" you shout in disbelief, grabbing some of the hair in your hands. Could it be? Are you getting your wish after all? But you still look human, even if your a lot bigger and stronger and faster.
What you can't really see yet, although there are already hints of it in your vision, is that your mouth and nose have long since fused into a single mass, and it's gradually starting to bulge out in front like an animal's snout. A car on top of the bridge blows its horn at the traffic, and you feel one of your ears twitch. Reaching up to feel it, you marvel at the long, rounded appendage your left ear has become. A quick check confirms the right ear is similar (and similarly mobile). It also dawns on you that one reason you're running felt weird is that you were running on your tiptoes pretty much the whole way, and you still aren't standing on your entire foot even at this moment. Taking a more attentive look down there, you notice your feet are splayed wide and your ankles are highly elevated, with lots more of that silky, mane-like hair growing on the underside of your arch--just the same kind that's grown out of your lengthening palms! Oddly, your toes have fused into two on each foot, and your nails are growing longer and wider. 'The beginning of hoofs maybe?' a doubtful inner voice asks from within your mind.
You're trying even harder not to get your hopes up this time. But why are your hands and feet starting to look like the lower halves of four classic unicorn legs? The odd nervous twitch at the end of your spine which started up during your frantic escape is really starting to feel a lot different now. A sudden surge of growth back there ends with something new dangling between your digitigrade legs: a long, skinny appendage ending in a huge tassel of that same hair as your mane and feet. A sudden impulse causes it to arch up behind you and twist around before settling back down to dangle where it was. Curious, you try to recreate those feelings and soon find yourself moving the object on purpose, noticing that it has a very long and snakelike range of motion. Resting it down behind your hocks again, you raise your tail again, this time up in front of you between your legs to see if you can grab it. Unfortunately, your hands don't have thumbs anymore, being just long pillars of bone with two toe-like "fingers" ending in split hoofs. You'll have to be content to hold your tail in front of you using its own muscles while you give yourself time to get a good look at it.
Horse tails aren't normally this long or flexible, and they generally have that sort of mane-like hair all over them instead of on the last few feet of it. Donkey tails end in tassels, but their tails are also not this long, and the tassel is just a short brush of hair rather than what looks like an entire horse tail at the end. None of the major equines have the split hoofs you're developing either. Bovines do, and they have long ropy tails almost like yours, but again not with the mane-like tassel. It's almost undeniable that you really are looking at a unicorn tail hovering out in front of you at your command. Your big, loud hard is quickening its pace and joyous expectation is starting to fill you, but there is one more change that would really confirm for you that what you wished for is really happening...
You feel it like a throb in your forehead that gets stronger and turns into a weight almost between your eyeballs. You can't see anything growing out at first, but you thrash your tail in joy when a pointy rod of bone-like material becomes visible above you. It's really true! You have a long, single horn growing out of your forehead! You lower your forefeet to the ground and prance around proudly, wondering what you should do first as a real-life unicorn! Are there others out there in a hidden magical world? Are you the only one? The first in maybe thousands of years? You don't know. You do know that you're not quite finished changing, but you're almost there. The hair you've already grown is long and feathery, and confined to specific places. Your last step is to grow short fur all over the rest of your body, and boy does that stuff feel great growing in! You've made it! You're mythical! You're strong, magical, and ready to run.