Author's Note

I had this written, but it was tough to edit. Don't worry if you follow the math as well as Rainbow Dash - it's there for anyone who wants to treat it as a puzzle. If you're willing to just accept that what in the end works ought to work and that nothing far short of it would, you don't need to pay THAT close attention.

Planning

Twilight slept. Partway through a dream about a book where the binding was a möbius strip so there was not only no cover but no back either, which made it even harder than usual to put down, she remembered she was supposed to be meditating.

So she was meditating. Sooo meditative, nothing going on in that mind at all. Get rid of the stupidly designed ludicrously long book, get rid of the library, get rid of the awareness of emptiness.

There was the ghost. It couldn't have possessed Flurry anyway, because it was locked away by Sombra. Only Cadence's attack on it had allowed any part of it to break free and influence ponies. The lock was very weird. What kind of key do you take, lock?

I take ritual. Sex. Perverse.

How much perversion do you need? If you're the lock, have we been feeling you, not Skyla, this whole time?

It gave her the spiritual equivalent of a befuddled look as if Twilight already ought to know all of this. This gradually solidified.

Do what you know you must.

You're not alive, not thinking, you're just a lock. But yes, in a way, I do, don't I? I need to get more information.

~~~~

When Twilight woke up, she remembered this vividly. Looks like I was on the right track with wanting that second memory potion!

She flipped out of bed, then bounded downstairs to get into motion. As she was just about to head out the door, she spied the familiar erlenmare flask left waiting for her; a scroll lay next to it. A little low-security, but I suppose it's not like anypony else could use it or even get into trouble with it even if they were silly enough to drink things unchecked. She opened the scroll and instead of a note from Zecora, found it was a copy for her of the spells Starswirl had transcribed for Starlight. Twilight set it aside and zeroed in on the potion. A sniff… yes, it was the same as before.

She hefted it up, and focused her alicorn energy into it. Her funneling energy into it did not go as smoothly as either of the first two times. Must be just woken up, or maybe still exhausted, or maybe the energy cost increases as I get to more and more memories? If so, this had better be enough to figure it out! The potion eventually changed color, and she immediately chugged it.

She was in a dimly lit catacomb, watching Sombra inscribe a magic circle around Skyla, who was bound. He was carving it in stiff clay with a stone knife Twilight guessed was an athame. He kept chuckling. He glanced up to a chalkboard, and moved on to the next section. Twilight walked over to the chalkboard and examined it.

The chalkboard was hazy. What was written on it kept shifting. Skyla probably didn't get a good enough look at it to remember. And I'm probably filling in details where she couldn't. Now that I think about it, this particular chalkboard is from Celestia's school, and I don't think she looted it from the Crystal Empire a thousand years ago. I should get back closer to Skyla to keep that from happening.

As she came back alongside the bound, ringed, and gagged alicorn, Sombra finished. "Finally. Do you know what I've been building here?"

Skyla shook her head.

"A magical machine to keep you alive."

Skyla's skepticism was obvious.

"I would like to live forever. But it is very difficult to test this without putting myself at risk of dying, isn't it? And none of my other prisoners are high-powered enough for this to work. So it's you. I do have to thank you for coming here after all, it seems."

There was a blur of motion as he got back to work and the memory fast-forwarded. It slowed as he got back up and addressed her. "Now… so long as your body remains, you can get back into it. It's your body, after all. If there is no body, then how do you find where to be? That is the hard part. For now, and for you, the best solution I can see is a ritual. You certainly love your rituals, don't you? Great or small, many little perverted ponies, or just a few very perverted, very indiscreet ponies."

Skyla shook her head urgently.

"But yes, you can't take that back. It's who you are now." There was a brief flash of the black/purple eye wisps that he later had, and Twilight realized he hadn't had them up to that point.

"So if you ever want to come back, that is the beacon that will work. And how convenient for me as well! I will get an impression to determine just what to look for…" He leaned forward and touched his horn to hers. Twilight realized she had to gain access, and jammed her horn in the gap and filled it with blank magic. Is this going to work? Can I really get an imprint off of a memory?

The memory of the blast of magic passed through her field. Though it did not have a direct effect on her magic, she could feel it, and shaped her own field to match how it would have been affected. She solidified her field just before the vision could end.

~~~~

"With that indirect impression of the lock, I was able to locate the actual lock and get a proper impression. It is the reification of this formula." Twilight pushed a sheet of paper to the middle of the map table. She looked around the table starting at her left - Tempest, Starlight, the bearers on their thrones with the crusaders and the crusaders' boyfriends in between, Starswirl, and Spike. She did not glance behind her right side to princesses Celestia and Luna, or behind to her left, to her parents.

Dash hovered for a moment to take a look at the formula. "Is it just me, or is this long, even for you?"

Twilight shook her head. "This is absurdly long. Each part corresponds to one of the specific fetishes that we've picked up from her. For instance, there being more witnesses to an act gives a bonus." She highlighted a section. "That lines up well with what you were imagining, and what Scootaloo has reported to have started imagining after you shared your kiss, and a number of others as well." She glanced to Rarity and Pinkie.

Fluttershy gulped. "Are we going to have to do everything in there?"

"No, not all. That would be impossible. The formula is not only huge; parts of it are a total mess. There are terms that are there, but they'll never amount to anything, like a fixed plus one point if there is at least one alicorn participating. There are factors of one, adding things that are subtracted back off. There are unachievable thresholds that look like accidents, like requiring more than the factorial of the factorial of six ponies for a particular size bonus, or requiring that the number of ponies in a daisy chain be exactly the square root of seven in order to get another bonus. So no, we can't do it all, let alone need to.

"But it will be a lot easier if we do at least most of the bonuses that are possible. For instance, from what you were imagining, impregnation gets a high base score, and there is a modest bonus for married ponies doing things with ponies not their spouse, but we can easily do without that."

Starlight asked, "What is the formula's overall shape? Or is it too much of a mess? I mean, you've only had a few hours to look at it…"

"It's not that bad, actually. The overall structure is simple, and the parts that don't do anything are mostly identifiable from a cursory inspection. So, you have an orgy. At it, each attendee gets a score based on some things they do and attributes they have. Like, ponies with two sets of genitals, or urinating on or into somepony, or doing something for the first time, or just being married, or wearing semen for an extended period, or having a large number of partners. That won't add up to much unless there are a lot of attendees. Second, each act gets a score, but for each pair of participants, only their highest-scoring act gets counted. So if you have four ponies and they each do all three of the others, we score six times. Third, each contiguous cluster of ponies all doing things with each other gets a score based on the network size and shape, but each category of network only contributes its best score. You add all of those scores up from all three categories, then multiply it all with the sum of the largest cluster score and the largest act scores for each act category - this can 'see' acts that weren't the best for that pairing. This has to exceed a threshold of a million points."

"Can you give some examples?"

"A simple case, yes. It isn't going to be very efficient. Ponies come into a room and all watch each other as they do random sexy stuff with one partner. No clusters… four for observers times the sum of one for kiss plus one for humping or toys plus two for oral plus three for vaginal plus three for anal plus five for impregnation… is sixty… it looks like we'd get around seven hundred points per act, so around fourteen hundred pairs of ponies would have to participate."

Rarity spat, "Almost three thousand ponies?"

"Only if every pony does one other. If they all do all of the others, it comes out much less. If we keep the observers, it's pretty much the square root of that, which is around fifty."

Celestia put in, "That seems doable, though not without consequence."

Button noted, "I don't feel bad saying I don't think I have the stamina to fuck fifty ponies in one session."

Twilight nodded. "We can do better than that. One of the main strategies is improving the multiplier at the end with the 'best' acts. In other words, have a small number of very perverted acts."

Rainbow Dash asked, "What's the most perverted thing you can do?"

"Well, if when I am one hundred forty years old or so, I come back in time, impregnate my younger self then commit suicide and get a noticeable chunk of my body eaten by participants, with ten thousand witnesses, that would completely do it right there. Ritual complete. If I could somehow arrange that future me didn't consent to this, we could get away with just a hundred witnesses. Or we could send my father, mother, or brother back in time when they are a hundred forty and do the same thing."

Night Light coughed. "I would appreciate not being murdered, even at a hundred forty."

Luna just said, "And I am glad to have confirmed that my abrupt obsession with death in sex is exogenous."

Twilight laughed. "So yes, we'll want to do without the factor of 4 from death and cannibalism, and I don't see how to arrange lack of consent, but if I send you back in time to score with me in every category, that's a very large bonus that might be enough that we don't need to bring in anyone not in this room."

Starlight followed up, "So, the perversions that help multiply everything are incest, death, cannibalism, witnesses, lack of consent, and age difference? The time travel is just to get that age difference?"

Twilight nodded. "Right. Also, any act which causes pregnancy gets the highest possible base act value, 5, even if it's dipping your hoof in semen and dripping it into yourself, which wouldn't otherwise even get a score. Also, the age difference bonus is the age of the older over 3/4 of the younger, the ratio rounded down, and it caps out at a five-times multiplier. Death triples, and cannibalism adds one to that factor, for four times. Factor from incest is 4 for nuclear family, 2 for aunt or uncle, first cousin, grandparent, half-sibling. Step-relatives don't count. There's technically a times 5 bonus for incest, but the criterion seems unachievable. The factor from witnesses is one plus the log base ten of number of ponies witnessing the act, rounded down, uncapped except by logistics."

Button fidgeted; Twilight pointed to him in acknowledgement and he said, "Isn't that anachronistic? I mean, logarithms were invented by Neighpier in the 600s…"

Starswirl shook his head. "Continuous logarithm, yes. The notion of counting powers like this was known."

"Sorry."

Twilight shook her head. "Don't be - it was good thinking. If there's any reason to think this isn't correct, we need to be on top of that. But it checks out with what we've seen. Whenever we did a kiss that had a sufficient age difference outside of family, that got a single point. For some reason, instead of making us get more excited and push towards unlocking, it… relieved the pressure. I have three theories on that, but it's aside from the point. Anyway, after a day, the point wore off and the orgy fizzled. Those of us who have done something that would get more points, such as nonmarital sexual contact, have had a longer reprieve. Whatever Rarity and Spike were doing apparently wasn't more than one point, since the thoughts returned after a day. What was it?" She looked to Rarity, then Spike.

He swallowed, looked to Rarity. She nodded, and he replied, "I sucked on her nipples."

Twilight closed her eyes. "That isn't a scoring act - it might count as kissing - so it is not evidence against. Phew." She turned harder to her right. "On the other hoof, Princess Celestia, just what did you do, to have your orgy technically still be ongoing?"

Celestia swallowed. "I… I find it odd that I am not panicking at the prospect of telling you. I will, however, say that this is not to leave this room." After reviewing the nods from everypony, she said, "I went to a nursing home for retired guards and palace staff. I identified a number of interested individuals, including one on the brink of death. He expired while in me."

"Ah. Even if nothing else happened, that would be worth… three for sex times three for death times five for age difference: forty-five. Squared: two thousand twenty five points. With the escalating decay rate, that isn't enough to explain it still going after, what, fifty days?"

"Other things occurred."

"If you tell me exactly what happened, I can check to find exactly when your thoughts should return. That would be a strong prediction and verification that this formula is correct."

Celestia nodded. "Three stallions and two other mares were present. We mostly snuggled and kissed, then writhed against each other. One of the mares came from that. I performed fellatio on one of the stallions. Another stallion mounted me. The second mare got on my back and the stallion mounting me performed cunnilingus on her. He finished in me, and the third stallion took his place in both regards. The first stallion came in my mouth, and I kissed the mare who had already come. The third stallion died amidst our mutual orgasm, and things ended."

"Did the second mare come? Were any of them married?"

"Yes, and the mare on my back was married to the stallion who mounted me first."

"I see." Twilight wrote some figures down, then said, "Then, that would be 6,532 points. That would take…" She checked a table, then stopped and slowly asked, "How many days has it been since you did this?"

Celestia considered. "Seven weeks ago as of this Sunday, starting just after setting the sun."

Twilight smiled. "Then we have a test. I am writing down a prediction of when your thoughts will return. We will wait until the day after that. If your thoughts have not returned by then, or if they return early, I have reduced confidence in this formula. If my prediction is met, then we can go ahead and proceed with more confidence." As she said so, she held up a sheet of paper, facing away from Celestia, on which she had just written, "Next Monday afternoon or early evening."

"Any other questions?" She looked around and called upon Spike, whose claw was up.

He asked, "Does the cannibalism require death and digestion? I mean, you said this is based around what weird thoughts we've picked up, and ah… my… I imagine putting her leg down my throat but then regurgitating it whole."

Twilight stopped, grabbed the scroll, looked it over, then realized it wasn't on there, and focused on recalling the spell. She slowly said, "Good catch. We do not need to kill or even cause severe permanent injury in order to take advantage of the cannibalism part - on its own, it will double. However, I don't think any of the rest of us are equipped to actually get enough of a participant down our throats besides you. Any others?"

Tempest coughed. "Does petrified count as dead?"

Twilight thought it over. "That's a good question. I think… no. But we may be able to pull some shenanigans with consent using it. Minimize the amount we have to do."

Rainbow Dash looked around the room. "Who actually wants to minimize the amount we have to do? Honestly."

Half the hooves went up. Twilight half-raised hers, and answered. "I want to make sure we get the job done. It's not obvious that we can do this without an extraordinary degree of effort, or bringing in more ponies. That could cause problems. So I'd like to minimize it to the point we don't need to use anypony not in this room, only have one pregnancy, and nopony dies or needs to do something they didn't agree to."

A silence spread, and Starswirl finally asked the big question: "Why? Why would the lock require all this?"

"I believe the particular requirement for witnesses or large number of participants or death was designed so that her return could not evade Sombra's notice. He anticipated being in control, after all. The rest was apparently from Skyla herself. It is not just a lock. It is also an attempt to pull her spirit in, gather her together. Attract her." Twilight turned to her right. "Princesses, what do you recall of princess Skyla?"

Celestia took a deep breath. "She ascended mediating a dispute in the aftermath of the end of Discord's reign. We first met her when she was seventeen. She seemed normal enough then. Eager. When we met her again, a few years later, she seemed oddly fearful of us, and yet attempted to seduce us. I am of mixed feelings about her return. When you told me that Cadence was not Skyla despite her similar talent and overwhelming similarity in coloration if not overall appearance… I was mildly alarmed. I had hoped Cadence was simply her, as she ought to have been."

Luna laughed ruefully. "She only shares mane and coat with Cadence, no more, not even body type. And she did not merely attempt to seduce me - when we last parted, I was not sure she did not bear my foal. Though we parted on not the best terms, I would definitely wish her to live again. She was very…" Luna trailed off, then suddenly declared, "She would beat you over the head with the greatest subtlety. Her plans hid plans - even the plans like 'attack ten on one' would be carefully selected and aimed. Though she lost to Sombra, her plots still planted the seeds of his defeat. Yet she… there was definitely something wrong with her. I think in this time she could get better. I believe you would get along very well, and she could be happy."

Celestia nodded. "I very much hope so."

There was silence, and Twilight looked down at the formula. Her eyes broadened from considering the math and took it in holistically as a representation of her being subtle rather than innumerate. And she blinked - diagonally through the formula were written the Old Equestrian imperative verbs for 'outsmart', 'act in stealth', and 'maintain purity'.

She snorted at that last one, then halted. I wrote this down fresh. She must be active in my mind to achieve that. She stared more intently and read down more diagonals. Gibberish until… 'Spirits?' She snorted and sarcastically observed, "No, reall–" Wait. 'Spirits', as in more than one? Did Sombra attach something to her and she wants to get rid of it? He also said 'this is what you are now'. They just said something happened to her.

Celestia asked, "Twilight?"

Twilight's mouth remained open. Act in stealth. "Well, ah… I'll make a simplified version of this formula and get anypony copies so you can plan out what we could do, see if there's a particularly efficient way of choreographing our orgy. Then we can do a dress rehearsal, and run the math. If our plan appears doable, we can go ahead. Nopony do anything you haven't done before, so we can keep any first-time bonuses."

The way everyone was looking past her and Fluttershy was petrified made Twilight turn around… and found Thunderlane. "Hi. I thought the room was locked."

Scratching his head, he said, "Yeah, Discord let me in so I could warn you the game starts in five minutes and anypony still in will be players. So uh, I could have sworn you just said, 'choreograph our orgy'."

Twilight blinked and realized she couldn't improvise her way out of it. "Yes, I did. It turns out that that strange magic thing was that there's an ancient alicorn spirit locked up, with ritual sex as the key. I want them to figure out how little we could get away with if we follow its rules, while I try to figure out how to attack the magic and bypass it altogether."

"Oh. Uh. I see. If there's anything I can do to help Rumble get free… uh." Then, to Fluttershy, "If that's all right with you."

Giggles went around the room at the reversal. After a few more seconds, Fluttershy's mortification softened. "It is all right with me."