Cassian stepped into the classroom and sighed, out loud. It didn't even echo a bit, thanks to how bloody full the room was. Every seat was taken, four House banners packed into one space like a poorly organised family reunion. The air already had that hot, crammed feeling, and they hadn't even started.
"Stupid rules," he muttered, dropping his bag on the desk and setting his mug down with a bit too much enthusiasm. "I told the Deputy Head my post-O.W.L. classes are just as full as the pre ones. They ignore it every damn year."
A few students chuckled. The ones near the front looked wary, like they were waiting for a hex or a rant. Probably both.
Draco and Potter stood up at the same time. They made it all the way to his desk before catching each other's eyes. Cassian watched the mutual glare, then the silent agreement to pretend the other didn't exist.
He raised an eyebrow. "What do you want? Thinking of taking over the lesson? Be my guest, really."
Both froze.
Potter cleared his throat. "Don't you need someone to cycle the Overhead Projector?"
Cassian gave a soft snort, almost fond. "I got my magic back, remember? You two are officially unemployed."
The realisation hit them half a second later. They turned in sync and slunk back to their seats as if they'd walked into the wrong broom cupboard.
Cassian waved them off. "Thanks for the offer though. Ten points to Gryffindor and Slytherin... mostly for reminding me I used to have unpaid interns."
He turned back to the rest of the class. "Where was I? Ah, right. The joy of being chronically overbooked. Everyone takes my class before and after their O.W.L.s, which means we cram the same bodies into the same room with half the ventilation. Tradition they asy. You know what it really is?"
A hand went up. "Unity?" Seamus said, like he was guessing an answer on a quiz show.
Cassian snorted. "Money. If they split the years, they'd have to pay me twice. Headmaster loves his gold more than a goblin with a ledger. I could put an invoice in the fireplace and he'd still argue the tax."
Some of the students laughed. A few looked faintly alarmed by the idea of Hogwarts budget priorities.
Cassian didn't sit. He paced a slow line across the front of the classroom, mug in hand.
"Alright. Now that we're all reminded of how criminally underpaid I am, let's actually learn something. Open your notes. Today, we're starting with the one topic everyone thinks they know and absolutely don't... The Goblin Rebellions."
The class stared at him in shock, wondering if Cassian really meant to teach that. Or if he'd finally snapped.
Cassian burst out laughing. "Imagine I actually taught that. Gods. Binns... Bless his racist ectoplastic heart."
The class burst into laughter.
Cassian shook his head, made his way to the blackboard, and picked up a stick of chalk.
Dark Creatures
He scrawled it in neat, sharp strokes. He'd got used to writing like this last year. When magic went, so did the floating script. Bit of muscle memory now. And honestly, it kept his hands busy when the class was full of barely caffeinated sixth-years.
He sat on the desk, gaze sweeping across them.
"This year, I've got a goal," he said. "So alongside the usual timelines, spell history, and some boring history, we're going to talk about Dark Creatures. And some of their counters. Bit of light magic too."
A few students stiffened. The Ravenclaws looked eager. Gryffindors looked interested. Slytherins... hard to read, as usual. One of them cracked his knuckles. Hufflepuffs were quietly panicking.
Cassian walked between the aisles.
"Alright," he said, eyes trailing the rows. "Who can tell me what a Dark Creature is?"
Hands shot up. Hermione's, of course. Daphne's too, high and quick. A few Ravenclaws followed, Lisa, Anthony, Mandy. Susan and Hannah raised theirs after a second's pause. Millicent looked like she might, then changed her mind.
Cassian nodded toward Hermione. "Granger."
"A Dark Creature is a magical being classified as such by the Ministry for its innate hostility, inability to be reasoned with, or dangerous magical properties."
"Sounds memorised," he said. "Source?"
"Beasts, Beings, and Boundaries. Ministry Edition."
Cassian made a face. "That thing's practically propaganda. But alright."
He turned. "Greengrass."
"A Dark Creature is typically defined as one whose existence presents a continual threat to Magicks or Muggles, either through behaviour or nature," Daphne said. "The definition shifts depending on the political climate and Ministry stance."
Cassian grinned. "Much better. Some Magicks hate centaurs. Makes them look too smart. So they call it dark. Simple as that."
A few students laughed.
He dragged the chalk down to underline the words.
"Dark doesn't mean evil. That's the first thing you lot need to unlearn. Most classifications are about control. If it can't be tamed or tossed into a nice little permit category, it ends up on the 'Dark' list."
He stopped beside Theodore, tapping his shoulder lightly. "Dragons?"
"Controlled breeding. Not Dark," Theo said.
"Right. Lethal flying lizards, fine. But banshees? 'Unacceptable in civil areas.' That's the quote."
He walked back to the front, leaned against the desk.
"We're going to study the ones that usually show up in your textbook index. The sort that don't fit neat definitions. Because those are the ones you're more likely to meet."
He looked around. "Who here's ever actually fought something Dark?"
Potter and Longbottom raised a hand. Obviously.
"Other than you two."
Dean hesitantly raised his hand. "We learned Riddikulus with Professor Lupin in third year. Sort of."
"Boggart, tame," Cassian said, "but alright. Did you win?"
"Er. Not really."
"Honest. I'll take it."
Cassian raised his wand. The shapes formed into view, first a Dementor, cloak dragging through the air without ever touching the floor. Its breath curled like frost. Students near the front flinched.
"Right," Cassian said. "Friendliest thing you'll meet on a government payroll."
The image drifted closer. Lavender squeaked. A few leaned away. Even some of the Slytherins looked uneasy.
"Dementors. Fed on happy thoughts, thick with depression, contractually obligated to ruin your day. You'll meet them outside prisons, during wartime, or when the Ministry's short on better ideas."
He flicked his wand. The image collapsed into fog, then reformed. This time, a wardrobe appeared. Slightly cracked. Shuddering every few seconds.
"Boggarts," he said. "Shapeshifters. Live in dark corners, wardrobes, cupboards, Professor Trelawney's filing system. They don't have a natural shape. They take whatever scares you most."
The wardrobe rattled again. A small bang. Someone on the Hufflepuff bench jumped.
"Key thing to remember," Cassian went on, "they're not trying to hurt you. They're shy, so they want you gone. Your fear feeds them though, but it's mostly a bonus not the goal."
He pointed. The wardrobe shifted. Briefly, it took on the shape of a giant spider, then a banshee, then a woman in lurid pink cardigan holding a clipboard.
A ripple of laughter went through the class.
He waved the spell onward. Another image sparked to life... The fog curled tighter, thinned, then reshaped into something far flatter, a black sheet, slick and twitching at the edges. It hovered just above the floor, soundless. The room seemed to get quieter. The shape drifted forward. Someone near the front pulled her knees up.
"Lethifold," Cassian said. "Also called a Living Shroud. Think Dementor, but worse manners and no Ministry leash. They slide under tents, through cracks, over your face while you're asleep. Then they squeeze."
The shadow dipped. An eerie scrape followed, though its body never touched the floor.
"They don't do soul-sucking or psychological torment. But they're silent and lethal. You don't wake up. You don't scream. You're just not there in the morning."
A few students looked like they'd forgotten how to breathe.
Cassian gestured lazily. The shadow curled up the wall, then dropped from the ceiling in silence.
"No one's ever seen its face. Mostly because anyone who gets close enough doesn't walk away."
He turned. The spell shifted. A ghost this time. Not one of the Hogwarts sort. Pale, sunken, robes hanging off it like old parchment. The eyes weren't blank, they stared, straight ahead.
"Wraiths," Cassian said. "Rare, hostile, and usually tied to cursed ground or bad binding magic. You'll know it's one of these if it doesn't blink and the air tastes like rotten egg."
The ghost turned slowly. A boy in the back muttered something under his breath.
Cassian waved his wand and the illusions froze in place, Dementor, Boggart, Wraith and the Lethifold, all of them hovering now.
The creatures loomed over the classroom, still as statues, and somehow worse for it. Students leaned back in their seats. Even the ones trying to look unimpressed weren't fidgeting anymore.
Better they were rattled now than arrogant later. He took a sip from his mug, then let his eyes settle lazily on the front row.
Cassian sat down on the desk again, took a slow sip of his tea, and nodded toward the lot of them.
"Now," he said, "for every creature up there, people came up with a spell to hold it off. I'm not saying 'defeat.' Not even 'kill.' I said counter. There's a difference."
He let the pause stretch.
"These things, most of them, aren't really alive. Not in the way you think. You can't kill what doesn't grow, doesn't breathe, doesn't age. You can burn a vampire to ash. You can pierce a basilisk if you're very lucky." He gave Harry a smirk. "But you can't kill a Dementor with normal means. You can only push it back. Which is where the term comes in."
He looked at their faces.
"Who can tell me what Amortal means?"
Hermione's hand shot up.
A few others hesitated but no one else followed through.
"Granger," he said.
Hermione sat straighter. "An Amortal creature is one that isn't alive in the traditional biological sense. It doesn't age. It wasn't born, exactly, or if it was, it's no longer governed by living rules. But it can be affected. Harmed. Possibly banished."
Cassian nodded slowly. "That's a good definition."
He pushed off the desk and strolled to the middle of the aisle.
"Amortal doesn't mean unkillable. It means the creature in question is playing by rules that don't match ours."
That got a twitch out of Crabbe.
"These aren't just monsters. They're leftovers of concepts that didn't fade when the world moved on. Fear given shape. Grief that kept breathing. Magic twisted around need, pain, old curses, old blood. They don't decay because they were never properly alive in the first place. And most of the time, if you're fighting one, it's because some idiot woke it up. So why study them?"
After a silence, Daphne said, "Because you can't fight what you don't understand."
Cassian tilted his head. "Exactly. You can't reason with something that doesn't care what you are. Can't talk down a thing that exists to consume. But if you know what it wants, if you understand how it forms, then you can stop it before it wakes. Or seal it before it eats a village."
A few grimaced.
Cassian sighed. "There used to be darker things than what you've seen so far. Amortals with no clear counters. No neat solutions."
Hermione's hand went up almost immediately. "The Dark King's army?"
Cassian gave a grim nod. "Yes. The Dark King's infamous army of amortals." His gaze drifted across the room. "No one really knows what happened to them. They vanished, one way or another. But there are... rumours."
A few students shifted in their seats. Someone swallowed audibly.
Neville raised his hand halfway, "I heard they were killed in Ash-"
"Amortals cannot be killed," Parvati cut in from the side.
A couple of others nodded in agreement, murmuring under their breath.
Cassian lifted both hands to his sides. "What Longbottom said isn't wrong," he said. "At least, not entirely. It's a common belief. Still just a myth, but one that's been repeated often enough to stick."
He paused, letting that settle.
"Here's the problem," Cassian went on, quieter now. "People hear something enough times, they start treating it like fact. Especially when it sounds impossible to challenge."
His eyes swept the class.
"Magic isn't limited," he said. "But it certainly cares what you think is possible. So don't let someone else's certainty become your truth."
This time, the class nodded more slowly.
He grabbed a bit of chalk again. Wrote two words beneath DARK CREATURES.
AMORTAL
NEGATIVE MAGIC
Then he underlined both, harder.
"This is the part they don't bother teaching you," he said. "Because it makes the world messy."
He turned. "Who here thinks Dark creatures are born evil?"
Susan shifted slightly. So did Leanne.
Cassian raised a brow. "Thought so."
He tapped the second word.
"They're not born evil. They're built from evil. Some by accident. Some on purpose. And all of them are shaped by negative magic."
Seamus frowned. "What does that mean? Curses?"
"Not exactly," Cassian said. "Negative magic isn't a spell category. It's an energy pattern. Think emotion. Intent. Pressure. Magic fed by panic, grief, rage. Repression."
He drew a crooked circle next to the word.
"That kind of energy builds. Sits in a space. Or in a person. If the conditions line up, if the magic's raw enough, old enough, it twists. Bends itself around what's already there. That's how you get poltergeists. That's how you get spirits tied to objects. That's how you get Banshees."
He pointed the chalk at the class.
"And if the magic's bad enough, if it festers for long enough, if someone adds blood or death or desperation to the mix, then you get something Amortal."
The class went very quiet.
Cassian turned back to the board. "You've seen it happen. Even if you don't know it."
He wrote again.
Obscurus
A few flinched.
"That's the cleanest example. Kid represses their magic hard enough, long enough, under the right pressure, and boom. Magic eats itself. Forms a parasite. They don't even know it's there, until it's too late."
Lavender raised a hand. "But isn't that just in theory?"
Cassian looked at her. "Tell that to the ruins they left behind."
She went quiet.
He nodded. "Obscurus is rare, yeah. But it's real. And more than that... It's proof. Magic isn't just light and wand-waving. It has a weight. You shove enough grief into it, enough hatred, it starts growing."
Ron muttered, "Like Umbridge."
Cassian didn't even blink. "She's just naturally venomous. No magic required."
Most of the class laughed.
He went back to the board.
"So here's the point. If you want to understand Amortal creatures, you start with the moment they formed, not the anatomy. What made them. What fed them."
He tapped the chalk against his palm.
"That's why counter-spells aren't enough. You don't just cast and hope it works. You match the source. You unravel the emotion that formed the thing in the first place."
Padma spoke up. "Is that why the Patronus works?"
Cassian grinned. "Someone's paying attention."
He pointed to her. "Yes. Dementors are one of the few creatures that respond to emotional magic. They're built from despair, from absence. So the only thing that pushes them back is presence. Hope. Joy. You have to outshine them with love, with pure positive thoughts."
He crossed back to the front.
"That's why the Patronus isn't just a charm. It's a state of mind. Positive magic weaponised. You can't cast it like Lumos. You have to fuel it."
He wrote again.
POSITIVE MAGIC
"The strongest spells in this category aren't incantations. They're reactions. You channel a real emotion through your wand, and the spell takes shape around it."
He paused.
"That's also why they're hard to teach."
A few nodded. Harry was already frowning at the desk, probably remembering every failed attempt.
"Everyone's got something different in the tank," Cassian said. "Some of you'll pull on love. Some on pride. Some on spite, frankly."
He looked at Draco, who was pretending not to look at him.
"The point is, you'll need to find what you've got to fight with. Magic responds to input. You feed it a feeling, it gives you something shaped from it."
He let that land, then tapped the board again.
"Magic doesn't forget," he said. "It enhances the state of mind, emotions, intent, mental visualisation. You pour enough of yourself into something, and it sticks. Good or bad. You ever love something enough to make a charm hold? That's positive magic. Now imagine the opposite."
The class sat stiff in their seats, every face fixed on the blackboard. Nobody blinked. Everyone had at least one memory rattling round their skull now... an artefact that hummed when no one was near it, a corridor that grew colder after sunset, or that one drawer in the Charms cupboard that never stayed shut. And that was just within Hogwarts.
"For years, I've been teaching you spell history. How intent shapes spellwork. How it's the spine, not the muscle. Without it, you're just waving sticks." He tapped the chalk twice against the board. "Thing is, I held back."
Hermione shifted in her seat. Zabini crossed his arms. Parkinson narrowed her eyes.
"Intent isn't just what you think you want," Cassian went on. "It's your state of mind made real. It's the current running under your thoughts. The thing fuelling the spell is what builds that state." He took another step forward, eyes sweeping the room. "You've all heard about the last battle. Dumbledore told his side not to use Unforgivables. No Dark magic."
He sighed. Turned on his heel, paced again. "Anyone want to guess why?"
Nobody moved.
Cassian looked at them. "Alright. New question. Hands up if you think you could use an Unforgivable Curse."
A few heads jerked up. The class went still again. No one raised their hand. A few looked at each other. Most thought this was some kind of trap.
Cassian nodded, not surprised. "Right. Let me change the question."
He stopped dead centre and lifted his chin.
"Hands up if you think I can use Unforgivables."
This time, nearly half the class raised their hands. Some slowly, some with absolute confidence. Potter. Granger. Daphne. Zabini. Millicent hesitated, then put hers up too. A couple Hufflepuffs looked unsure, glanced at each other, and followed.
Cassian smiled, crooked.
"I can't."
Every hand dropped.
"It's not that I don't know how. It's not about magical strength, either. I could match the theory. The pronunciation. The force. But I couldn't make it work."
He leaned back on the edge of the desk, arms folded.
"Because to cast a Dark spell... real Dark magic, the kind that doesn't fade with sunlight, you have to feed it something. And what you feed it stains you."
A few students looked rattled now.
Cassian shrugged. "Dark magic taints your soul. That's real. You can't wave a wand and walk away clean. The magic remembers. Remember this always. Magic remembers even if you forget."
He nodded toward them.
"And once your soul's marked like that, light spells stop answering properly. You can't cast a true Patronus anymore. Healing magic starts slipping. Charms backfire. It's structure, not punishment."
He drummed his fingers on the desk.
"There are exceptions. Always are. A rare few can use both. Light and Dark. Not in balance, don't believe that fantasy. I mean actually split. Part of them feeds one side, the other does the opposite. Usually those people are bloody miserable."
He gestured loosely.
"Love turned into obsession. Hope twisted into delusion. Loyalty curdled into worship. Courage bent until it became martyrdom."
He let out a sigh.
"But those people are often fragile as hell. It takes a shattered kind of mind to hold both threads without tearing."
Cassian looked out over the room.
"So no. I probably couldn't cast an Unforgivable if I tried. And I'm fine with that. Honestly, I hope none of you can either."
The silence that followed was heavy. Like they'd just heard something they weren't meant to know until years down the line, when it might've been too late to take back.
Cassian took a long drink from his mug.
He raised a hand. The wand flicked. Light coiled above the desk, nothing fancy, just a wisp. But it pulsed, warm and quiet.
"That's the kind of magic I want you to use. Not because it's nice. Not because it looks pretty in a duel. But because once you learn to wield this..." He tapped his chest. "You won't need Unforgivables."
He let the light fade.
Then he grinned, wide and sharp.
"Besides, you've got me. I'm better than a curse."
Someone choked a laugh. Someone else sighed hard.
"Right then," he said, shaking off the weight. "Homework's cursed objects. Due Monday. If you ask for an extension, I'll curse you."
A few nervous laughs broke the tension.
But nobody forgot what he'd just said.
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