"The one with the power to vanquish the Dark Lord approaches...born to those who have thrice defied him, born as the seventh month dies...and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not...and either must die at the hand of the other for neither can live while the other survives...the one with the power to vanquish the Dark Lord will be born as the seventh month dies..." - Sybill Trelawney
All the Ways he Knows Not.
2. Equals
Everyone knew this day was coming, ever since Harry and his friends managed to collect and destroy all but one remaining horocrux, Nagini - Voldemorts snake familiar. Said snake was suspended high near the candles in a floating cage, captured by Harry and Tonks. The day when Voldemort would attack the school.
The battle during Halloween in Harry Potter's 7th year was fierce. Over 70 Deatheaters had invaded Hogwarts and were slowly winning. The battle had devolved into various pockets of fighting, as most battles do.
Harry Potter and Ginny Weasley were double teaming Voldemort in the grand melee inside the Great Hall, but steadily loosing ground under the much more powerful magics and casting abilities of the Dark Lord.
Ron Weasley and Hermione Granger were watching their backs and making sure no Deatheaters got Harry and Ginny from behind.
Lupin was in a life-or-death duel against Fenrir Greyback, the werewolf that cursed him, while nearby, the Weasly twins, Professor Flitwick, and surprisingly Draco Malfoy were facing off against a beserking Belatrix Lestrange and four other Deatheaters.
Somehow, next to them, Neville found himself facing off against his worst nightmare, a sneering Severus Snape.
"Give up, Longbottom! How could you expect to go against a wizard of my caliber when you could never even brew a potion that worked!" Snape said while casting a horrible yellowish curse that Neville barely dodged.
"You're right, professor." Out of all the things Neville could have said, this was not on the list of expected responses in Snape's head. The Gryffindor boy continued, placing his left hand in a robe pocket. "You're right. I could never make a potion that actually did what it was supposed to. Not ever. Only later, did I discover the permanent chaos hex someone placed on me, Professor Snape. Sometime around first year, perhaps during the first class I've had with you. In fact, I figured out why every single potion I've ever made only ever did one, and only one thing."
And with that, Neville pressed down on the flasks' stoppers, deactivating the unbreakable charm, pulled them out of his pocket, and flung 5 glass test-tube-like containers in Snape's general direction.
Snape's eyes widened as he hurriedly cast a physical shielding and reflection charm, just in time.
The flasks hit the rubber shield and bounced off unpredictably. Then everything seemed to happen at once.
A flask flew upwards and impacted Nagini's cage. The explosion was deafening. Bits of metal and snake distracted everyone, including Voldemort, just as he was casting a rapid fire cutting curse at a bleeding and almost incapacitated Harry Potter.
The Dark Lord spun around to look at what happened to his familiar at the last moment, and the sickle-like magic blades missed Harry entirely, and jetted in Neville's direction - actually grazing him across the head.
Another vial landed on the ground in front of Bellatrix, making a massive crater and flying shrapnel. When the dusk cleared a little, the torturer of the Longbottoms and killer of Sirius Black fell over - a jagged shard of stone floor stuck in her skull.
Two other vials landed in the Great Hall, one destroying the Ravenclaw's table, the other taking a chunk out of a wall, but not hurting anyone.
The last vial, though, fell right onto Voldemort. And in one massive thundering flash, 3/4ths of the now mortal Tom Riddle's head ceased to exist in any form not resembling chunky salsa.
Everyone who had a mark on their arm suddenly fell to the ground writhing in pain as the dark magic tried to heal a very very dead Voldemort without much luck. Instead, it only ripped the life force out of all his followers. The 47 Deatheaters that were still alive and fighting suddenly weren't either.
Neville looked up at his concerned friends and allies, wiping blood from his forehead.
"And the Dark Lord will mark him as his 'equal'... literally" Harry quoted as he looked at the two thin even parallel lines the Dark Lord inadvertently cut on Neville that now stood out like the mathematical symbol. "I guess you were the one the prophesy mentioned all along."
"I.. what?" Neville exclaimed, confused.
"You killed him. You killed Voldemort with an exploding potion." A bloody Draco dragged himself over to were people started to gather, staring at Neville. "Hey.. you know what this means?"
Draco looked at Harry and smiled. "Hey, Potter! How does it feel to be 'The-Boy-Who-Lived-To-Be-A-Decoy?"
Harry Potter just groaned and passed out.