Umbridge inwardly congratulated herself for a job well done, as she eagerly observed the results of her announcement unfolding before her eyes. The last time Umbridge had inspected this class, Trelawney had rattled off a so-called prophecy predicting You-Know-Who's return, and claimed that Oleandra Greengrass had been the one to have recited it first.
In Umbridge's eyes, neither of them were True Seers; Oleandra Greengrass and Sibyll Patricia Trelawney were both frauds, and dangerous ones at that. As far as she could tell, this whole predicting You-Know-Who's revival was all a plot by Dumbledore to undermine the Ministry's authority. Obviously, this would not do, so she had immediately begun the procedure to remove Trelawney from her post, and her efforts were now coming to fruition.
Umbridge could tell that some of the students idolized the Divination teacher; the children listened to her, believed that she could divine the future. But she could not accept this! Trelawney could not be allowed to continue poisoning students' minds! Which was why Umbridge was determined to humiliate her in front of her students…
But to Umbridge's astonishment, instead of snivelling and begging for mercy like she had expected her to, Trelawney sat up straight in her armchair, her hands gripping into the fabric of the armrests like an eagle's claws. Her eyes had grown milky; her gaze, empty…
And then, twin voices joined as one, unearthly and steeped with power.
"THE DARK LADY WILL RISE... WHEN THE VEIL BETWEEN WORLDS GROWS THIN AND THE STARS ALIGN… SHE IS ALREADY AMONGST US… ABOMINATION AGAINST NATURE, BEARING A WAND OF YEW… MADE MONSTER BY HER PEERS, THE CHOSEN ONE SHALL IN TURN CHOOSE HER AS THEIR FINAL FOE. ALLIES SHALL TURN AGAINST EACH OTHER… SIBLINGS SHALL FIGHT TO THE DEATH… THE DEAD SHALL TREAD THE LAND ONCE MORE. FOR AS LONG AS THE DARK LADY YET LIVES, THE DARK LORD SHALL ENDURE. ONLY THE CHOSEN ONE MAY CHOOSE… PARADISE ON EARTH AWAITS... ONLY THE CHOSEN ONE MAY CHOOSE…"
"This is some sort of trick!" Umbridge screeched. "You— you— Dumbledore put you up to this!"
"I'm sorry, what were you saying?" said Professor Trelawney weakly. "I didn't quite catch that…"
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Merlin and Oleandra looked at each other awkwardly under the shade of the World Tree. Indeed, Oleandra was back here again, just like when Merlin had first pulled her consciousness out of her body in her third year, to allow her to pass on a prophecy in Trelawney's place.
"Er… I'm sorry?" said Merlin tentatively. "I suppose I might have forgotten to cut the Wyrd connection between the two of you…?"
Oleandra simply glared at him and put her hands on her hips. Merlin was clearly taking the piss out of her; that was the most blatant lie she had ever heard, and she had heard some pretty wild ones.
"Ugh, you Greater Fairies and those eyes of yours," said Merlin in disgust. "Okay, fine— I kept the connection on purpose. Are you happy, now?"
"Why in the world would you!?" Oleandra sputtered. "And no, that doesn't make me happy in the slightest!"
"Well, the thing with prophecies is that they're like safety relief valves on a pressure cooker," Merlin explained. "You see, time is like a river that flows ever forward; it's possible to pop back for a quick visit, but it's impossible to alter the future by changing the past, since it's already happened from your perspective. And as time flows, the current of fate builds up pressure; influencing future events to go into certain directions. It's very energy efficient for the world to do so, you see, since it limits the energy expenditure for the generation of potential futures; which consequently increases its lifespan."
Merlin coughed into his fist, having gone on an unnecessary tangent about the nature of existence.
"Ahem. At any rate, when the pressure gets too great, fate's got to let off some steam, which escapes as prophetic vapours. Usually, it will happen to a Wizard sensitive to fate, a Seer, when they are in close proximity to either the object of a prophecy or to someone who will have great influence on said object."
Oleandra didn't bother wondering why a fifteen-hundred-year-old man knew about modern Muggle kitchen appliances, even though he was stuck inside a tree outside of time and space.
"The last time, you got me to make the prophecy instead of Professor Trelawney, because taking my end-of-year exam before Harry had disrupted the flow of fate," Oleandra said irritably. "So, which is it? Am I outside of fate's influence, or am I included? And what's your excuse for making me recite this new prophecy, this time? I can sort of hear what's going on outside, and I'm fairly sure Trelawney's reciting the same prophecy along with my body."
Merlin sighed and looked upwards to the branches of Yggdrasil.
"You weren't subject to fate at first, but it's caught up to your existence; Viviane and Morganna were never supposed to escape the world-between-worlds in the first place. But you are now, because this new prophecy would never have come to be without you," he said sombrely. "You see, fate doesn't care which future ends up being chosen, but I do. By allowing you to make the prophecy as well, I'm lessening the odds of you being chosen as its object; since who would suspect the prophet of being the object of their own prophecy? Only a few paths lead to the best possible outcomes, but you becoming the Dark Lady is not conducive to that purpose. The only thing I've ever wanted is a brighter future for everyone, you know."
"How'd you even know all this?" Oleandra asked.
"I believe your shadow-selves have already explained their theories on this subject," Merlin said most unhelpfully.
The long and short of it was that every parallel world's Merlin was destined to be trapped inside the World Tree from the moment of their birth, which is why none of them had resisted Viviane's sealing magic. The World Tree encompassed all of space and time (except the future, because it hadn't happened yet), so Merlins were able to look sideways through time to observe other World Trees; parallel realities; what-ifs.
However, even if some realities were nearly completely identical to this one, they weren't necessarily perfectly aligned along the time axis. In other words, events in those other realities didn't happen at the same time, allowing Merlin to see potential outcomes in alternate realities whose clocks ran a little faster, which somewhat allowed him to guess at his own original world's future.
"I believe you when you say you want to make the world a better place," said Oleandra with a sigh; she'd been worried about being a pawn in Merlin's plans, but it seemed like she had nothing to worry about on that front. "Well, go on, where's the step-by-step guide to a good ending?"
Merlin smiled melancholically at her.
"Knowledge of the future changes the future, mate," he said sadly. "You'll have to figure it out on your own, or else that future might never happen. I can't tell you anything important, as much as I'd want to. If I had any advice to give, it'd be to keep your friends close; especially next year. And yes, that includes the annoying Malfoy boy. You'll regret it if you don't."
"Very helpful," said Oleandra sarcastically. "Where's the other bloke, by the way? The mysterious-looking fellow, he was here last time."
The World Tree and Merlin were beginning to fade; Oleandra's spirit was being drawn back to her body. It was time to say goodbye.
"Oh, and I was sorry to hear about Viviane's passing," said Merlin mournfully. "Of all the women I've bedded, she easily counted among the top ten— no, scratch that— the top three."
Oleandra made a rude gesture in Merlin's direction, and then she was gone.