Fraudulent Wizard

 It's lucky the sleeves of these robes are so big, or I couldn't get away with half the stuff I do.
 It's also lucky I have a proficiency for tinkering and machines.
 When they asked me to levitate a feather, I pretended to struggle for a bit then excused myself to the bathroom and threw together a compressed air shooter. That's the easy part. Activating a device up your sleeve and making it look convincing with the wand is the hard part.
 That's the third piece of luck: I've always had a knack for sleight of hand. I expect these three things have used up about all of the luck for my lifetime.
 After a few more waves of my wand with no result, I start pulling the string attached to my device with my left pinky while my right hand holds the wand. Lightly, at first; I observe the other student's progress from no levitation to full levitation and try to make mine look similar. Eventually I blow enough air to shoot the feather up in the air, then ease off so that it's just held in place while beaming proudly at the teacher.
 "I never doubted you'd do it for a second," said the teacher, "You always seem to come around after a good bathroom break. Some alone time to clear your head and think does us all some good when puzzling a difficult problem."
 To my surprise, many of my classes didn't require me to pretend. Potions was close enough to chemistry that it came to me easily, and astronomy wasn't much different than what I already knew. Herbology was just taking care of plants, albeit with more rules, and my sister had enough plants that I already had a vague familiarity with the subject. History of magic was history. It was entirely new to me, sure, but the process of learning and retaining facts was the same.
 Charms, defense against the dark arts, and transfiguration were my real testing grounds.
 When they taught us how to make fire, I started having to make modifications to my "wand" (I've been told actual wands are constructed a very specific way. I just have a stick I carved to look like the others.) This was a big enough job I couldn't do it in the bathroom and had to wait until the next day. I hollowed out the wand and created a modular plug which feeds into a tube that leads to a small hole on the end of it, small enough that it shouldn't be noticeable except under scrutiny, especially with my ability to subtly direct people's eyes.
 Into this tube I inserted a small flamethrower. The next day in class, I told the teacher I'd figured it out overnight and she was delighted to see my progress.
 Thus far, I'd been trying to keep distant from my classmates to prevent anyone from getting too close and discovering my secret. But after a couple weeks, I decided I needed a confidant. Someone I could trust. That Harry Potter kid seemed trustworthy, but he had too much attention on him. It would be nice if I could get someone from my own house, but a lot of them are too uppity for this role. (The sorting hat had placed me in Ravenclaw, and knew my secret right away. He promised to keep it just to see how things played out.)
 No, what I need is a Hufflepuff.
 For the next week, I analyzed my classmates and considered my options. Eventually I selected Winston. He had few friends like me, so he should be easy to get on my side, and won't have anyone to blab to. (This train of thought made me reconsider if maybe I should have been in Slytherin.) He seemed like a nice kid, one that would be understanding of my situation.
 I started sitting next to him in class and making small talk with him. Laughing and cheering along with him when he finally got a spell, and him doing the same for me. We starting making a solid rapport based on mutual struggle and success.
 After building up our friendship for a week and a half, I decided to reveal myself to him.
 We had a class on the mending spell, which was easy for me. We just had to repair a pair of glasses. While no one was looking, I slipped out a small welding tool, wiped away the excess with a cloth, and cooled it.
 "Hey look, I got it!" I said to Winston.
 He looked over, completely unaware as he was so focused on his own spell. "Wow, good job!" he said.
 "Thanks!" I quiet my voice to a whisper. "Hey, watch this." I smash the middle of the glasses against the corner of the table and snap them in half again."
 Winston scratches his head. "Did you just do that so you could cast the spell again and show off?"
 "No. Watch." I turn and angle my sleeves so he can see them, and fix the glasses again, all while not touching my wand at all.
 His eyes widen, and I give him a smile. "Meet me in my room later, I'll explain."
 Later in the day I hear a knock on my door, and welcome Winston into my room.
 He gets straight to the point, as always. "What was that? Were those muggle tools?"
 "Yeah."
 "Why are you using those? Magic is so much easier!"
 "Because I'm a muggle."
 He laughs. "Yeah, right. Like a muggle can spew fire out a wand."
 "Look." I dig in my trunk and pull out my tiny flamethrower. I shoot it into the air, then show him how it connects to my wand.
 He shakes his head in disbelief. "How did you even get here?"
 "I'm not sure."
 He begins to say something, then stops. "There are a million reasons that doesn't make sense, but I guess it doesn't matter. Why are you doing this? Why not come clean?"
 I honestly hadn't thought about that, so I did now. After pondering for a minute, I formulate a response. "To see if I can, I guess. It's... Fun."
 "Fun?"
 "Yeah. It's like... Magic. But not real magic, the magic muggles (I still feel weird saying that word) do where they trick people into thinking they're doing magic by being clever."
 Winston let out a deep sigh. "Why are you telling me this?"
 "Because you're my friend." I felt a bit bad for that. It wasn't totally a lie, I really did like Winston, but that was a carefully constructed sentence to get him on my side.
 That got a smile out of him. "Aww, well, how can I say no to that?" Another twinge of guilt. He clapped me on the shoulder, and thus started a beautiful beneficial relationship.
 For the next few years, Winston helped me hide my secret and perform some of my more convoluted stunts. When they wanted me to cast the cheering charm to make people giggly, I whipped up some laughing gas and sprayed it through my wand no problem. When they wanted me to shrink a spoon, I prepared a smaller spoon and swapped it out. When they wanted me to unlock a chest, I made some lockpicks and deftly used them while diverting attention with dramatic waving of my wand.
 Of course, I couldn't pull everything off, and got the occasional failing grade. Sure, I could make a cup that looks like the rat-cups the other students were turning their rats into and slip the actual rat into my sleeve, but making it seem like a living being was a bit too far even for my skill at illusion.
 The relationship with Winston wasn't one-sided, of course. With the subjects I could help him with, I helped him as much as humanly possible; I would have felt incredibly guilty otherwise.
 As the years went on, this school seemed to become increasingly dangerous, however. Students getting frozen, giant snakes, things with robes that suck your soul out? All revolving around that Harry Potter kid, thank god I didn't befriend that guy. Still, I felt increasingly unsafe, and then one day inspiration struck me. It happened when that year's defense against the dark arts teacher, Mad-Eye Moody, went way off script and taught us some things he shouldn't have.
 That same year, this guy named Voldemort came back. He was apparently like the boogeyman for wizards. The next year, Winston managed to guilt-trip me into joining some club Harry Potter was making to oppose Voldemort. He convinced me I had to share my secret with them and use my unique skills to help them. They were all shocked to learn my secret, but they greatly appreciated my assistance with machines. It started to feel like they were my friends, too.
 Eventually we somehow wound up on some mission to the Ministry of Magic. A fight with death eaters ensued, which I mostly hid throughout. I had my secret spell, but no desire to use it, and didn't trust my ability to hold up against these crazy spells being thrown around everywhere.
 While peeking out around a corner, I saw that Voldemort himself had shown up. Fear caught in my throat, but at the same time the frightening sight sparked some kind of inspiration in me. Here was an opportunity. If I didn't do something now, I may never get a chance.
 Like I'd been doing for years, I waited for the right moment. The moment when he, and enough of his goons, were sufficiently distracted. I stepped out from behind the corner, drew out my ultimate spell from my sleeve, and aimed my hand at Voldemort. Not having to yell out the spell's name before using it, I found, to be a great advantage.
 I pulled the trigger on my homemade revolver, and watched a red spot appear in Voldemort's forehead, followed by his body slumping to the ground.
 "Avada kedavra," I declared.