A/N: There are no such thing as glamours in canon HP. The only perception magic I can think of is the disillusionment charm. There don't appear to be any spells where you can just wave your wand and make things look different.
So what if we set about fixing that?
Neville screamed as he fell from his broom, landing with a loud "crack!" on the ground. Madam Hooch stepped over to inspect his injury.
"He broke his leg," she said. "I'll take him to the Hogwarts Infirmary. Nobody touch their brooms until I get back or I'll have you expelled faster than you can blink!"
Madame Hooch paralyzed Neville with a quick spell then floated him away from the practice field. Neville whimpered as he was taken away.
Draco inspected the ground where Neville had fallen.
"Look!" he cried. "The big lump dropped his Remembrall!"
Draco picked the object up, idly tossing the glass object in the air a few times. Every student watched to see what he would do.
Draco cocked his arm back and chucked the Remembrall as far away as he could. It landed on a grassy field, many meters away.
Draco laughed and loudly said, "what a loser" before striking up a conversation with Pansy Parkinson.
Hermione moved to go retrieve the Remembrall, but Harry held his arm out to stop her.
"Harry," she said quietly, "I need to get that back for Neville. It was a present from his grandmother, and he would be upset if it got lost because I didn't do anything."
Harry chuckled at that. "You're quite the hero, Hermione. Are you sure the Hat shouldn't have put you in Gryffindor instead?"
Hermione frowned at Harry.
"Maybe in Hufflepuff with Neville because you're such a good friend?" he said tentatively.
Hermione continued to frown at him.
Harry sighed. "All right, all right," he said. "You don't need to bother looking for the Remembrall because I nabbed it when Draco wasn't looking."
Harry pulled the small glass ball out of his pocket to show Hermione.
Hermione was shocked. "How did you do that?" she screeched.
"Keep your voice down!" Harry hissed. Fortunately, Draco didn't seem to notice Hermione's outburst.
"I didn't even see you move," she said in a quieter voice.
Harry just grinned. "I should hope you didn't."
Snape started the class by taking roll call. He stopped as he reached Harry Potter's name.
"Ah, yes. Harry Potter. Our newest..."
The words died on Snape's lips as he saw the wide grin on Harry's face and the barely-contained energy that left Harry bouncing slightly on the edge of his seat.
"...celebrity."
Snape shook it off and continued to take roll call.
Once that was done, he addressed the class. "You are here to learn the subtle science and the exact art of potion making," he said softly. "As there is no foolish wand-waving or incantations, many of you will hardly believe this is magic. I don't expect you to understand the... Potter, cut that out!" Snape yelled.
The last sentence was delivered to Harry Potter, who was quite visibly bouncing on his seat. The student sitting next to Harry edged away from him. This was partly from the weirdness of Harry's behavior, and partly to keep Snape's wrath from falling on her.
"I can't help it sir, I'm too excited!"
"Be excited on your own time!" Snape snarled. "I have no use for hyperactive children who can't even follow instructions."
"But sir, this is Potions!" Harry exclaimed.
"Your stunning command of the obvious does you no credit," Snape stated acidly.
"No, I mean..." Harry struggled for words. "I've been looking through the potions books assigned, and you can do all sorts of amazing stuff with potions! Skelegrow! Polyjuice! Felix Felicis! I'm just really excited to learn to brew potions myself."
Snape sneered. "We shall see. The potions you mention are NEWT-level potions, and I only accept the best of the best into my NEWT-level Potions classes. I very much doubt you have the composure or focus necessary to make the grade."
Harry slumped back in his seat and mumbled to himself, "Look beneath the underneath."
"What?" Snape demanded as he slapped the surface of Harry's desk. Snape leaned into Harry's personal space.
Harry straightened and challenged Snape's gaze. "I said, I'm looking forward to it."
"That will be two points from Ravenclaw for your cheek, Potter," Snape said. "Now everybody open your book and turn to page 4."
"I can't believe you did that!" Hermione exclaimed to Harry as they left the Potions class.
"I can't believe his breath is that bad," Harry stated seriously. "I thought I was going to gag when he leaned in to talk. Seriously, hasn't that guy ever heard of breath mints?"
"Troll - in the dungeons - thought you ought to know," Quirrell gasped before collapsing in a dead faint.
Harry smiled, a dangerous gleam in his eye. A split-second later, he was gone from view.
Hermione, who had been sitting next to him, turned to Harry to ask him a question that died on her lips. "Harry? Where'd he go?"
Several seconds later, Harry was making good progress towards the dungeons when he spotted a shallow trench dug along the floor. It went two different directions: towards the Hogwarts dungeons and towards an area that only contained some empty classrooms and a girl's bathroom.
Quirrell had said the troll was in the dungeons, right?
Harry took off in that direction.
Snape may have been rude and caustic, but he was not an idiot. The Philosopher's Stone was held at Hogwarts. An emergency was in progress that drew everybody's attention away from the Stone. It was an obvious ploy to Snape, which is why he jogged towards the third-floor corridor to investigate whatever Quirrell was attempting.
Snape rounded a corridor and saw a shallow trench dug through the floor. At the same time he heard a rustling noise just to his side. He spun to see who it was, but nobody was there.
Slightly unnerved, Snape continued towards the third-floor corridor.
Above him, Harry Potter held onto the chandelier hanging from the ceiling. Once Snape was gone Harry let go of the chandelier, landing completely unhurt thirty feet below.
Harry followed the trail to where it terminated. Unfortunately, there was nothing there but an empty crate of meat and a smashed wooden door that led outside. Harry could reconstruct the scene easily enough: the troll (and whatever it had been dragging) had wandered close to the castle, smelled the meat, and knocked down the door to get at it. From there, it must have gotten confused and started wandering through Hogwarts, where Professor Quirrell spotted it and ran to the Great Hall to warn everybody.
That meant that Harry had been going the wrong direction. Harry became a blur in black robes and shot back the way he came. Less than a minute later he found something. One of the doors to the empty classrooms was vibrating like there was something very heavy behind it, trying to get out. Harry was positive that this was the troll.
"Well, let's help with that," Harry thought. He was about to cast an opening spell on the door when it burst open and the troll came barreling through. The troll stank like rotten garbage. It had grey rubbery skin and a grotesque expression on its misshapen face. The troll regained its bearings and yelled rage at the world.
"Well, aren't you a beauty," Harry whispered admiringly.
Unfortunately, the troll noticed Harry and swung a large wooden club straight down at him. When the troll lifted the club up to inspect the damage, there was nothing there but a large crater.
"That thing has to weight close to a hundred pounds," Harry said conversationally, now somehow behind the troll, "and here you are, swinging it like it's nothing."
The troll spun around awkwardly, swinging its club horizontally at the sound of the voice. The club smashed into the wall, knocking off large chunks of plaster. Harry winced. He hoped he didn't get blamed for that.
"HARRY!" a voice yelled out. Harry looked up. It was Hermione. This was a particularly unfortunate time to be distracted, because just then the troll's club came hurtling at Harry a third time. Distracted by Hermione's cry, he didn't notice the club until it was too late. It cracked Harry solidly across the skull and the momentum threw him down the corridor where he slammed into a wall.
"HARRY!" Hermione yelled again, drawing the troll's attention. As the troll passed Harry he concentrated through the headache and made a sign with his hands. Suddenly the corridor was filled with copies of Harry, each one yelling at the troll and trying to draw its attention. The troll went berserk, swinging its club all around itself, trying to end the sudden overload of stimulation. Every time the club made contact with one of the Harrys the clone disappeared in a puff of smoke.
Unnoticed by the troll, the real Harry made his way over to Hermione.
"Hermione," he shouted to be heard above the troll, "you have to leave right now. I promise I'm not in any danger, but you have to go."
Hermione shook her head stubbornly. "I'm not about to leave until you're safe."
Harry groaned impatiently. "We don't have time to argue about this. I'm fine, you have to go."
Hermione frowned. "Not without you!"
Harry groaned, looking back at the quickly thinning shadow clones he left to distract the troll.
"Ugh, fine," Harry said.
Harry Potter picked Hermione Granger up over his shoulder like a sack of potatoes and started to run away from the troll.
Unfortunately, the troll had cleared out all of the clones by this time and spotted Harry running away. It was too slow to catch up with Harry itself, so it did the next-best thing and threw its club. Harry didn't see this, but Hermione did. She screamed right in Harry's ear.
Harry didn't know what was coming, but he had mere seconds to act. He used a substitution technique targeting the first thing to enter his line of sight, and hoped that it would be big enough to take the damage in his place without being too big to swap places with.
It was quite unfortunate, then, that Professor Snape rounded the corner at that moment.
Professor Snape was in a foul mood. He had gone to the third-floor corridor to prevent the Philosopher's Stone from falling into the wrong hands. It didn't look like Quirrell had been there, but that blasted three-headed dog had been. It grabbed him by the leg with its mouth and tossed him around like a rag doll. A well-placed stinging hex had allowed Snape to escape, but he would walk with a limp for the next few days.
As Snape was heading back he heard a loud commotion. The commotion was coming from an area that normally didn't have students at this time of day. Forgetting about the troll momentarily, Snape strode out with the intent of yelling "What's going on here!" when he felt a sudden disorientation-
-and a large wooden object smacked into his gut, knocking him to the ground. A troll twenty meters away was charging towards Snape.
"You dare?" Snape asked furiously.
The troll howled with pain and rage. Harry briefly looked behind himself to see what was happening. Snape had somehow arrived and was facing the troll, cutting large slices in the troll's flesh with an unknown spell. Dark blood spurted from the troll's wounds as it staggered forwards.
"Yeah, we're good," Harry said. "Let's go."