Your skin starts to turn green and your hair starts falling out around you. You catch it falling in clumps, trying to place it back on your head, to no avail.
"What's happening to me?" you ask in a much more nasal voice.
"Ah, I was right to expect you'd be a good handyman for me," said the witch.
Claws sprout from your fingertips. You flex your fingers around a bit, feeling them get even more nimble even as your claws grow longer and sharper.
"Tell me," she says. "Have you always been good with gadgets?"
"Heh, heh, yeah," you find yourself laughing mischievously, even in the midst of your plight, for reasons you can't quite place. "I can fix anything," you go on, "when I'm not breaking it to see how it works! But what does that have to do with--?"
"With your change? Every human has some of the old fair folk lineage these days, as far as I can tell. It probably has something to do with all the changeling children and those various one-night stands with the fox women and the succubi back in the middle ages. I suspected, all along, that you had something of the gremlins in you. Perfect to enhance some of the tech-related hexes I have to practice in this modern age."
Your ears grow out to sharp points beside you, and you feel your teeth lengthen inside your mouth. Your clothes feel baggy, and that's how you realize you're shrinking. You look up at the witch, and you notice every wrinkle on her middle-aged face, even in the night, as your vision gets crisper and more detailed. You've heard of gremlins: active little creatures that can make or break almost any human invention. But you thought they were just a figure of speech, like storks making babies or Santa bringing presents at Christmas. Who could have known that you actually were one all along, or that you would become one when exposed to the right magic?
"Let's go back to my place," says the witch. You start off to follow her on your little legs, hoping the walk is not too long. For someone who just changed into a fairy tale creature, you're already awfully bored for some reason. The witch hands you a smartphone. "Here, knock yourself out," she says slyly.
"Ooooh, hehehe!"
Your sharp eyes zero in on the places where you take it apart. Your sensitive green fingers start digging into it. A strange magic power starts flowing back and forth, giving you ideas for hexes you can put on it--or help the witch put on it later. Being the her familiar for a while is going to be fun if you can play with toys like these!