It took an embarrassingly long time for Mercy to realize the nature of the twisted world she now inhabited.
She didn't realize it when she struck out at Weiss Noir, and watched him fall like a common pony to her venom. He was unprepared for her to actually shatter the chains he put her in, and the blow was too quick for anyone in the room to have possibly stopped her.
She didn't realize it when the princesses disappeared as soon as she spoke. Adrenaline could excuse many things, and she had more to worry about than what could make two alicorns suddenly disappear.
She sensed that something was wrong when, after escaping through the tunnels and murdering her way through what few guards remained there, she encountered gigantic random beasts roaming the frozen north, in quantities far greater than normal. Was this a ploy? A contingency by the mad sage, to unleash monsters upon his demise?
No matter what it was, it meant she had to be careful, she snuck and slithered and hid, coasting on her internal reserves to get her through the north at a reasonable pace, and then, into the badlands from whence she came. Back to the Changeling Hive. She strongly suspected that the foolish unicorn hadn't told anyone of the hive's location before his death, if he had, his pathetic 'mercy' would have been meaningless. The Princesses, the Longma that remained, they would swarm towards the location of the hive and scour it clean of all life.
She knew something was very wrong when her demands to see Chrysalis were met with immediate obedience from the changelings at the hive's entrance. She knew something was terribly wrong when the changeling queen, upon hearing her ranting and raving at the betrayal of handing her over to the mad sage, ceded command of the hive to Mercy, and offered her the full resources of changeling kind in a tearful admission of guilt.
But all of that paled in comparison to what had finally made Mercy realize that none of this was real. One simplistic thing that finally broke her suspension of disbelief, something that no convoluted blend of magic and pure luck could have possibly made reality.
She had begun testing once again, cutting into cadavers and live subjects alike to further her knowledge of biology, chiefly the strange and bizarre creatures that constantly attacked the hive and herself on a daily basis. She investigated odd ruins that had not been there before, and sought out solutions to the dark problems that threatened her from within them.
As she studied these things, she finally realized the falsehood of her senses, for the simple fact that she experimented upon things to learn their nature, and every theory she made was proven correct.
Science was Mercy's deity, and she knew well the foibles of her chosen idol's mythos. The eyes and ears of a snake were tools for the discovery of truth and knowledge, not arbiters of what it was. Only by proving theories wrong could one discover the theories which were closest to correct, and, on rare occasion, discover which theories were so close to correct as to be indistinguishable from it.
Was this dragon-like creature that belched elemental fury at her army of changelings a creation of the Shadow Realm? "Sure!" her tests answered merrily.
Was this ancient relic that she found in an underground temple secretly tied to the changeling race in some way? "That sounds about right!" a cursory examination dictated.
She couldn't find a way to break whatever illusion she was under, any words she spoke were fact in this twisted realm, any assumptions she made were law. The only things that seemed immune to her newfound ability to simply wish into existence or out of existence whatever she so desired were subtle things, no matter how often she said it, she could not demand her own death. She could not demand a total cessation of this false reality. She could not influence the odd beasts and quirky events that befell her constantly, until she had resolved them through murder or pointlessly clever puzzling.
She found that she could wish to see reality, but it was fleeting. To make that wish would place her in a cell, where she was embedded in a sculpture of a tree, gazed upon by pitying ponies. A tube quietly fed her a thin trickle of nutrient-rich fluids.
But this too, was an illusion. It took moments for her to find a way to escape, when she did make such a wish. At first, it was subtle. A guard's inattention left her time to slowly wiggle her way out of the sculpture over a period of weeks by shedding her skin and rapidly accelerating her own metabolism. It took a month for her to even suspect that she hadn't truly escaped that time, and another week before she was driven mad with the desire to see reality once again.
Now that she knew the fleetingness of that particular command, the illusion grew less subtle in its methods by which to cast her out of her prison and back into perceiving her total domination of the world.
A guard slipped and smashed into her prison. Suspicious of it being another illusory trick, she allowed herself to be recaptured.
A dragon attacked. Weiss's blatant punishment of whatever dragons broke into his realm caused a war, and in the frantic battle, her prison was ripped apart, and she fled. It took a week for her to realize it was another lie, and to wish her way back into the tree-statue.
Sombra returned, and demanded she return to his side, ripping his way through everything with disgusting ease.
Now, the illusion had abandoned all subtlety, and simply used the same excuse each time. Within a week, Queen Chrysalis's mind magics would, as far as she could tell, breach her mental prison, insisting that she had found a way to get the snake out of the illusory world, by transferring her mind to a changeling using the Archive Mind, the magical web of changeling personalities that they kept their minds in when their bodies and spirits failed.
It took Mercy a very long time to attempt another 'wish', the first time this had happened, but with but a single demand to see reality, an entire year after that, her new life as a changeling queen at Chrysalis's side was abolished from her sight, and the cell her crystalline tree was planted in was her world once more.
She had been placed in her own personal hell, a world in which science and truth did not exist, only hedonism, excitement, and theorizing in ways that held no meaning.
With a grimace, she ignored yet another "psychic broadcast" from Chrysalis, begging her to allow the queen to free her mind from her imprisonment.
She blankly stared at the guards watching over her cell. How long would it take this time? How long would she be able to see the bland reality of a few punch-card officers trying to while away their shifts, before her existence bled back into vivid, colorful falsehoods?
She noticed something in the corner of her cell. A spot that seemed darker than the rest.
As she observed, the spot began to grow, until none other than the Sage of Darkness stood before her. His arms were crossed, and he had a self-satisfied look on his face.
"Power is an illusion. Absolute power... A seamless illusion," he began by quoting.
"Go away," Mercy snarled.
Weiss's smirk turned into a grin, even as he appeared to melt before her eyes in a way that looked utterly agonizing. It would have been a delight to the sadistic snake if it had been real.
"That's fine. I can see you aren't ready for my offer. I'll be back in a decade or two," he says in a burbling tone as he dissolves into a puddle of molten pony.
A decade? She would be mad by then. (As if she weren't already insane from this sisyphean torment)
"Show me the real Weiss Noir," she demanded suddenly.
Suddenly, it was if nothing had happened, he stood in front of her once again, in the exact same pose, with the exact same cruel smile.
"Ahh... Perhaps you are ready, then."
Mercy dearly wanted to say 'get to the point,' but held her tongue out of fear for what hallucinations would come if she spoke a command. She didn't want to believe that this was real either, but Weiss had never broken character in any of her dreamlike fantasies before. If it was a new trick to fool her back into the sludge of unintelligent complacency, then she lost nothing by engaging with it.
She wouldn't be able to tell if it were true or not, after all. Even if she tried.
"I'll begin with the stick," he said conversationally, looking around and waving to motion to everything around her.
"This is your existence now. Forever. You are forever banished from reality, doomed to persist in this new world of confused dreams and entertaining nightmares," he explained simply.
"Did you like the one where I had a meteor crash into the planet, and your changeling scientists figured out how to use its cells to make supersoldiers? I stole that little idea from a videogame, but it was still pretty fun to watch," he said, slowly drifting off-topic.
Weiss shook his head, returning to the subject at had. "But then, I wouldn't be here without a good reason. You see, I've found myself in need of something. Something critical to my revenge. Something you helped take away from me."
His grin reminds her of Sombra, in the worst way.
"Talent."
He looks up to the ceiling, and his smile fades as his hands clench into fists.
"This place... These immigrants that I've allowed to become new citizens of my realm... The quaint and curious things I've done to entertain myself... They're all means to an end, and yet, they just aren't enough. I can't trust all of these strangers, all of these random individuals, with their own wants and needs, with their own allies and friends. I'm losing the ability to understand them. But you? I can understand you. I've decided to form a Council, with you as its first member. A council of trusted individuals with talents I can use, who can advise me in ways friends and strangers cannot."
He smiles.
"You killed my best doctor, so there's a position open. I've gotten quite a bit of enjoyment out of reading some of your notes, and you're perfectly qualified," He says in a detached, unhinged way that manages to disturb even Mercy.
He holds out two of his hands, and slowly opens them, revealing two pills.
"You take the blue pill, and the story ends. You go back to Wonderland, and I stop letting you have these little conjugal visits to the real world."
Mercy would quite literally choose anything else.
"But, take the red pill, and..."
He pauses, trying to think of something clever to say.
"Why are you doing this? Even you can't be so idiotic as to think it's a good idea to try and recruit me, even if you know I will say yes," Mercy demands insistently.
He chuckles. "Wasted opportunity," he mutters as she interrupts him trying to think of a quip, before considering her question and responding with a shrug. "Come now, Councilman 'Oh Goodness', you know what they say," he begins, stating her new codename.
He continues to hold out the two pills. "Keep your friends close..."
Weiss bows remorsefully to Celestia and Luna as guards carry away the tree containing Mercy, hauling it onto an extremely large chariot.
"I had no idea what she was capable of. She was somehow able to poison herself with a drug I suspect was smuggled into the prison, and I only just managed to prevent the worst with some hasty action on my part. I can't afford to try and keep her imprisoned any longer, and I dread to think of what would happen if she refuses to pass on to the next world. The contingencies in her physical body alone..." he shudders.
Luna shakes her head. "You couldn't have known. It is unusual to imprison a criminal in Tartarus while still alive, but it is neither the first nor the last time we have done so. You did the right thing, coming to us, Weiss."
Weiss rises, blinking a few tears from his eyes. "Thank you, Princess. It's... hard for me to accept help from others. I didn't want to do this, but this had to be done," he says quietly.
Celestia nods. "You may have your 'polls' and 'votes' to act as tools in steering your realm, Lord Weiss, but there is no shame in asking for assistance with things beyond your means. If there is a criminal or foe beyond your ability to contain, then we are more than willing to aid you in keeping such evil at bay."
He sniffs a bit, and rises to his full height. "You're right, princess."
After a pause, he manages to smile, his malicious, knowing smirk a familiar sight for the two princesses by now, the expression failing to evoke unease in the pair like it perhaps should.
In one of his claws, he palms a small trinket idly. A Black Materia that the princesses don't pay much attention to, one containing a special, unique version of the Shadow Clone spell, keyed to a single individual. A new form of hatred had bloomed inside the sage, incomprehensible to anyone but himself as he held the orb.
"I'm going to need all the help I can get."