Harry meets Kali in the forbidden Corridor, she was perched atop one of the Imp's heads still in her bat form... It was an odd sight to be honest...
She transfers to his shoulder and allows the Imp to teleport away, "Shouldn't you still be in class, master?"
"I got out early."
"After causing an uproar I imagine..."
He shrugs noncommittally, "Have you checked the defences yet?"
She nods, "War-time fortification wards, fortunately, their only purpose is to prevent us from accessing this area from an unauthorized direction.
"War Wards...? Why not just ward the door and be done with it?"
"I have no idea, master. Perhaps it is exactly as it presents itself, a trap." Kali offers.
"Let's spring it then." he mutters, stepping through the door only to find the three-headed dog unconscious, much to his disappointment... He'd been hoping to put the abomination out of its misery. "Kali..."
"It's better this way... We won't alert the Headmaster to our intentions, or the fact that we were here at all."
...
"Fine." he grouses, telekinetically shifting the giant dog to reveal the trapdoor.
The next few 'obstacles', if you could even call them that, were laughably easy to bypass. Some kind of plant that Harry forced away with a gout of fire, magically locked door that was resistant against unlocking spells... But not from mundane lockpicking as it turns out, neither were amused when Kali clicked it open with ease.
A giant chess set that Harry blasted apart, magically repairing all of it after the door opened.
A troll, which Harry was about to blast apart when Kali stopped him, forcing the creature to sleep.
A set of three potions positioned in front of a floor covered in colourful flames. Harry simply took control of them via blood magic, temporarily turning them green and opening a path.
Last... Was a mirror standing in the centre of a blank room...
"Hmm..." Harry lets out an annoyed hum.
"Master?"
"It's nothing... I'm just..."
"Disappointed?"
He nods, "Disappointed. Unless this mirror leads to an alternate dimension made of gold, this will have been a massive waste of time and effort..."
Letting out a sigh, he walks in front of it and peers into the reflection. At first it's just him standing there with Kali perched on his shoulder... But things slowly started to contort, colours phasing in and out, until the reflection was completely unrecognisable.
Now there were two figures standing in the centre of a burning hellscape. Brightly glowing green meteors showered down from the sky, crashing into the landscape around them and destroying everything in their path yet leaving the figures unharmed.
He recognised one of the figures... Kali. She was leaning heavily only the taller figure, pushing her breasts against his side while his clawed hand rested half on her hip and half on her butt. She was staring up at him reverently, eyes wide with awe and tongue skimming her lips with what seemed like anticipation.
At both of their legs was a huge bone-white snake, that looked like a grown-up version of Nanthisk...
It was the last figure that took Harry's attention however. Tall, broad, with an aura of visible power. He had no skin, merely thick grey scales that looked sharp, vicious, yet durable. Glowing green lines traced between them, thrumming like a heartbeat. He only wore thick black leather trousers and a torn bloody white shirt that appeared far too small for him.
His face was utterly demonic, glowing eyes streaming with green particles, as if his power couldn't be contained to its physical form... Sharp, horrific teeth protruded from its almost lizard-like mouth, and large horns protruded from its forehead which separated the long, silken yet tangled pitch-black hair...
Harry's mouth goes dry as he slowly recognises it, the figure in the mirror tilting its head as if it acknowledging him... That was him... Or at least, what he wished to be.
"K-Kali... Are you seeing this?" he questions breathlessly.
She nods her head, "Yes... Who knew Mother could show such a face..." she mutters, her bat form's face grinning almost manically.
"Mother...?" he pauses, his composure returning to him, "I-I think we're seeing something else..." he looks up and spots some writing at the top of mirror, "Mirror of Erised...? Oh... Desire..." he concludes, simply reversing the words.
"Desire, hm...?" she turns towards him, "What do you see master..." she hops closer to his neck, rubbing her furry body against him, "I'll tell you mine if you tell me yours..." she utters lasciviously.
Harry blushes, head turning away from her, "N-no... I-I'm not interested in what you saw..."
She giggles at his distress, "Okay, master. We'll just have to make it a reality then... Won't we?" she gives his neck a small nibble, causing his body to tremble all over.
Shaking his head, he turns his attention back to the mirror and approaches it. His demonic reflection does the same, and once they are face to face, or rather, face to chest, the creature shows him something...
It raises a clawed hand that was clutching a small red stone. Its mouth falls open, allowing a green mist to escape, "Evermore." it rasps in an inhuman voice before dropping the red stone into its pocket. Harry's eyes widen as he feels the weight of it, pulling out the same stone from the mirror.
He stumbles backwards, Kali flapping into the air in response, "What is it?"
"A stone! The mirror gave me a stone!" he displays it to her. The stone didn't glow perse, but it definitely gave off an unnatural aura. Magical... Highly so. Enough that even a Muggle would be able to feel it.
"Just what kind of artifact is that...?" she utters, shocked.
"Magical stone... Not a gem, no obvious magical effects..." Hary mutters to himself, it's not green so it couldn't be jade, a stone with many myths surrounding it... "Any ideas...?"
"Hm..." she leans in and takes a deep smell of it... She Kept her eyes closed as she ruminates on it. "Crystalized Magic... But I can't identify its attribute..."
"Crystalized?"
She nods, "Solidified and highly compressed... There's enough magic here to wipe all of Britain and a good portion of France and its neighbouring countries off of the map..." she admits, causing Harry to almost drop the thing.
Who could stay calm when literally holding multiple nukes in the palm of their hand!?
"Don't worry. It seems to have stabilized itself. When magic is drawn out it will recuperate with ambient magic, it won't store more than this however... Whoever made it designed it as such...
"We... We should leave before someone finds out. Before the Headmaster realises we stole his weapon of mass destruction..."
"Good idea."