In the words of the great Bard: "Omigod, we're back again." Here's something short and sweet to advance the plot.
"The absolute stupidity! I don't know what the hell I expected from you lot, but fighting a fully-grown mountain troll? That takes the pumpkin pasty right there!"
Harry leaned back in his hospital cot and rolled his eyes. A small bandage was wrapped around his head where he'd struck the wall. His friends weren't unscathed, either. Ron's waist was wrapped in bandages, Hermione had a bloody nose, and Fred/George had broken legs (the same leg, which made it still impossible to tell them apart). Only Morty was unharmed, although his power armor had run out of juice, so he'd had to be dragged to the Infirmary by Hagrid. He lay frozen in place on the bed next to Harry, staring up at the ceiling.
"Pure, unadulterated stupidity!" McGonagall wrapped up her rant and sighed. "However, you did manage to defeat a danger to the school, so there must be some credit given." The students glanced at one another, smiling. "There will be no points taken, but no points lost."
"Ah, students!" Dumbledore breezed into the Infirmary, eyes twinkling. "Fighting a full-grown mountain troll? Quite the achievement. Six hundred points to Gryffindor."
"Albus, I will end you!" McGonagall screeched, wheeling around in pursuit of the Headmaster.
"Well, that sure was a sticky situation," Harry said. "Good thing you guys are alright."
"Speaking of which, where the hell were you?" Morty asked, turning his head with the greatest difficulty.
"I was following Snape up to the Third Floor corridor."
"What?" Hermione spoke up, "Snape was going for the Stone?"
"Yeah. Fortunately, ol' Fluffy used him as a chew toy for a few minutes before the greasy shit gave up and hobbled away."
At that moment, a shaken and bloody Potions Professor staggered into the Infirmary, gripping several of his fingers in his one un-mauled hand. "Pomfrey!" he hollered, before falling over in a dead faint, scattering digits across the floor.
"So, what have we learned about the Philosopher's Stone?" Harry asked.
"Don't you mean the Sorcerer's Stone?" Morty asked.
"...Fuck off. Hermione?"
"Well, we know that it was created by Nicholas Flamel, and that it's hidden in the school, and that Snape wants it."
"So we've learned nothing."
"Pretty much. If only we had access to the restricted section of the library."
"To get in there, we'd need, like, an Invisibility Cloak or something," Ron said. "By the way, Merry Christmas, everyone."
"Thanks, shall we open our presents?"
"Ok. Harry, how about you open that Cloak-shaped package first."
"Alright… huh, speak of the devil. An Invisibility Cloak."
"Convenient," Morty remarked.
"I know, right?"
"Almost too convenient."
"Don't kill the mood, Morty. It's not like fortunate coincidences will be handed to us endlessly these next seven years."
An awkward silence fell over the group of friends. "Open my present, Harry," Ron said.
"Wow, a sweater. Neat."
"...You don't like it."
"I didn't say that. Don't put words in my mouth. Here, I'll put it on. Wow, it is itchy."
"It's made of badger wool."
"I didn't know badgers had wool."
"They don't. It's just badger hair my Mum glued onto a cotton jersey."
"God, you're poor."
"...Yeah."
"Stop pushing me, Ron," Harry whispered.
"Not my fault, Hermione's elbow is in my face."
"On second thought, we shouldn't have all tried to fit under the Cloak," Morty remarked.
"Yeah, it's a bit cramped under here."
"Neville? The fuck are you doing here?" Harry asked.
"I've been with you guys all day. We opened presents together."
"I was wondering where the pathetic aura was coming from. Go back to the common room, Neville, and take your stupid toad with you."
"I don't have Trevor with me."
"Ribbit."
"Trevor! How long have you been here?"
"I had no idea books could scream so loud," Harry remarked, slamming the classroom door shut and pulling off the Cloak.
"We'll try again tomorrow," Hermione said. "It's too dangerous with Filch and Norris on the prowl."
"Where are we, anyway?" Harry glanced around the empty room. Empty, that is, save for a large, Baroque Rococo mirror in the center of the space. "Huh, interesting mirror."
"A little too ornate for my tastes," Ron said.
"If you could afford it, you'd probably think differently," Harry replied.
Ron walked over and looked at his reflection. He jumped back in surprise. "Woah!"
"What?"
"I'm Head Boy, and Quidditch Captain."
"...Have you gone mental?"
"No, look."
Harry walked over and glanced in the mirror. "All I see is a black-haired dude and a red-haired lady."
"Who are they?" Hermione asked.
"Damned if I know. Morty, what do you see?"
"I see myself standing over Rick's dismembered corpse."
"...What?"
"I mean, I'm the President of the United States."
"Boring."
"What kind of mirror can do this?" Hermione asked, glancing at her reflection. She was in bed surrounded by a handful of stable boys (and Ron, for some reason), but thought better than to mention it aloud.
"A magic one?" Morty suggested.
"It is the Mirror of Erised." The First-Years jumped as Dumbledore's voice spoke up behind them. "It shows the viewer his or her greatest desire."
"Oh, that explains the backward writing above the mirror," Ron said.
"So you solved the puzzle."
"It wasn't that hard to solve. Where did you come from?"
"A man must have some secrets," the Headmaster replied, tapping the bridge of his nose.
"Were you hiding under that desk in the corner?" Hermione asked, gesturing to the item of furniture.
"...No."
"But why is this here?" Harry asked.
"It's been placed in my care for the time being."
"Like the Philosopher's Stone?"
"Sorcerer's Stone."
"I swear to god, Morty."
Dumbledore tapped his nose. "I cannot say. I'm afraid that is something you young children should not worry yourselves with."
"Did you just wink at us?"
"...No. By the way, nice Invisibility Cloak, Potter-Sanchez. Five hundred points to Gryffindor for good fashion."
Several floors away, McGonagall sat up in her bed. She didn't know why, or how, but somewhere at that moment, Dumbledore had done something that would give her hell to deal with in the morning.