Deprimo Profundis is the incantation for the "Deep Plunge Charm," an 1832 modification by the Hogwarts Dueling Club.
At the time, the so-called modern Levitation Charm was widely used—and even abused for pranks—due to its simplicity.
A certain female Head of Ravenclaw reverse-engineered the spell and discovered that "making an object rise" and "making it fall" were essentially just different waveforms of the same set of gravitational interference commands.
It is said that when she wrote the derived formula for this "Deep Plunge Charm" on a piece of parchment, the ink suddenly bled straight down through the grain of the wooden desk until it cracked the floorboards on the third floor.
The casting motion for this spell is the exact opposite of the light, upward swish of the Levitation Charm. The Plunge Charm requires a sharp downward slash of the wrist, like swinging an invisible war hammer directly onto the target's center of gravity.
The effect causes the mass of the struck object to increase exponentially for a brief moment, while its volume remains the same—a feather can smash spiderweb cracks into floorboards, and a book can bow a bookshelf.
If cast on an object that is currently under the effects of a Levitation Charm, the two opposing forces will create a brief moment of static suspension before the object plummets downward at double the speed.
To this day, the wizarding world still debates whether this spell should be classified as "Dark Magic."
The troll stared blankly for a second, raising its disproportionately tiny head. The next moment, its own heavy weapon came whistling down, smashing brutally into its bald skull.
BANG!
The troll swayed a few times before crashing to the floor, shaking the very floorboards beneath them.
Harry and Ron stared at the scene in absolute shock, completely uncomprehending how Ron's spell had suddenly become so miraculously powerful. Hermione crawled out of her stall, her face pale as a sheet and her entire body trembling, but she still managed to look around the room.
"Stop staring! Run!" Harry grabbed Hermione's arm.
The three of them stumbled out of the corridor, running smack into Professor McGonagall and the others who had hurried over upon hearing the noise. Julien, however, had long since faded into the shadows on the other side of the corridor and quietly slipped away.
He knew that Quirrell's plan for tonight had failed. The Sorcerer's Stone was safe, and the seal on the stone tablet remained undisturbed. As for himself, hidden in a corner no one knew about, he had become... a watcher?
He cast one last look at his friends—who were currently receiving a stern dressing-down from the professors, though entirely unharmed—and a relieved smile touched the corner of his mouth.
---
The next morning, the air in the Great Hall was filled with the usual scents of toast, smoked bacon, and butter.
But today, thicker than the smell of food was the endless buzz of conversation. The story of Harry, Ron, and Hermione bravely fighting a mountain troll had spread through the entire castle overnight, as if carried by a Sonorus Charm.
"Did you hear? Three Gryffindor first-years actually took down a troll!" Over at the Hufflepuff table, Hannah Abbott's eyes were wide with amazement. "Ron used the Levitation Charm to lift the troll's club and knocked it out cold!"
"And Hermione!" Justin Finch-Fletchley added from beside her. "She was trapped in the girls' bathroom but she didn't panic at all! She was the one who told Ron which spell to use!"
The Gryffindor table, meanwhile, was a sea of jubilation. Percy Weasley sat with his back perfectly straight, loudly and fully "reconstructing" his younger brother's "heroic deeds" to anyone who would listen, his face glowing with secondhand pride.
Surrounded by students from every year praising them, Harry, Ron, and Hermione sat in the middle of it all, their cheeks flushed pink.
"Headmaster Dumbledore personally awarded Gryffindor thirty points!" a senior Gryffindor shouted. "We've seriously closed the gap with Slytherin now!"
Amidst the cheering, the Slytherin table remained dead silent. Draco Malfoy sat with a dark scowl, gripping his silver knife and fork so tightly his knuckles squeaked. He glared at Harry, who was surrounded by admirers, jealousy practically spilling from his eyes.
"It was just dumb luck!" he muttered bitterly to Crabbe and Goyle. "A Mudblood, a Weasley pauper, and a Savior who's all talk. How on earth do they deserve points?"
Crabbe and Goyle nodded repeatedly, though they didn't dare agree too loudly. After all, the tension from the troll's rampage last night hadn't fully settled, and they certainly didn't have the guts to publicly question the Headmaster's decision.
In the Ravenclaw corner, Edgar Finch pushed up his glasses and cast a suspicious glance at Julien, who was slowly cutting his sausage. "I have to ask, Julien. Did you really go to the girls' bathroom last night?"
Casen Moretti leaned in as well, his face full of probing curiosity. "Yeah! And... Ron can barely even levitate a feather on a good day. How could he possibly lift a troll's club all of a sudden?"
Julien looked up, flashing an innocent smile. "Maybe the sheer panic unlocked his hidden potential? As for me," he shrugged, "I probably just took a wrong turn. I ended up following the crowd back to the dorms later; you guys just didn't see me."
Edgar wanted to press the issue, but Casen pulled him back. "Forget it, forget it," Casen lowered his voice. "Maybe he really did eat something bad! But seriously, Gryffindor's luck is insane. Thirty points!"
Julien just smiled and didn't explain further. He knew his roommates' suspicions weren't unfounded, but some things simply didn't need to be said out loud.
---
Following the troll incident, Harry, Ron, and Hermione had become incredibly close. The minor frictions of the past had completely vanished in the face of a shared life-or-death experience, and the three were now practically inseparable.
However, they were often seen huddled together in a corner of the Gryffindor common room or in a secluded section of the library, whispering amongst themselves, their eyes filled with secrecy.
Julien occasionally caught glimpses of them gathered around a crumpled piece of paper, arguing in hushed tones, or whispering over a thick, ancient tome. He knew exactly what was going on. They had to be trying to figure out the three-headed dog guarding the forbidden corridor on the third floor—and what secret it was hiding.
One afternoon, after finishing History of Magic, Julien was strolling along the path by the Black Lake on his way back to Ravenclaw Tower when he spotted Harry, Ron, and Hermione in the distance. Their heads were ducked, and they were walking quickly toward Hagrid's hut on the edge of the Forbidden Forest, looking urgent, as if they had something important to ask.
"Looks like they couldn't resist going to Hagrid for answers," Julien murmured to himself, pausing to watch the three figures disappear through the hut's doorway. He knew that with Hagrid's personality, there was a very high chance he would accidentally let slip more clues about the three-headed dog and the Sorcerer's Stone.
Sure enough, after returning from Hagrid's, the trio's research sessions became far more frequent. They spent increasing amounts of time buried in the library, scouring books on magical creatures, ancient treasures, and modern magical masters.
One evening, while Julien was in the library looking up books on celestial magic, Hermione suddenly crept up beside him, looking slightly hesitant. "Julien, have you... have you ever heard of Nicolas Flamel?"
Julien looked up, blinking in feigned surprise. "Nicolas Flamel? Yeah, I know him."
"What! You know?! You're not joking?!" Hermione was genuinely shocked this time.
"Doesn't everybody know him?" Julien said, pointing to a Chocolate Frog wrapper sticking out of his pocket. "He's on the Chocolate Frog cards, isn't he? The greatest alchemist, invented the Sorcerer's Stone, lived for hundreds of years?"
Realization dawned on Hermione's face, and her eyes instantly lit up. "Right! The Chocolate Frog cards! How did I not think of that?!" She threw out a hasty "Thank you!" before spinning around and sprinting back to where Harry and Ron were waiting nearby. The three immediately huddled together to whisper excitedly.
Watching them go, a faint smile touched the corner of Julien's mouth. He knew the truth of the Sorcerer's Stone was slowly unspooling for them, but this was the path fate had set. He didn't need to intervene.