All magic in the setting is accomplished by Mysterious Old Women.
The deal is, if you find that you are in desperate straits, you can go for a walk in the woods or sit quietly somewhere outdoors looking despondent, and if you're lucky - well, arguably lucky - a Mysterious Old Woman will appear. She will ask you what's troubling you, and then offer her advice. You can decline the offer at that point and no further trouble will ensue. If you accept, however, she will give you some strange instructions, which you must follow to the letter or you will find yourself giving birth to a carnivorous lizard or some such unpleasant consequence. If you succeed in following the instructions exactly, your problem will be magically solved.
Mysterious Old Women are wise, knowledgeable, and benign. They always mean well and they're usually pretty good at designing solutions that will genuinely work. However, they operate under a number of constraints:
- There is a three-way tradeoff among the magnitude of the solution, the complicatedness and precision of the instructions, and the magnitude of the disaster that awaits failure. A more complicated and powerful solution will lead to a bigger disaster if instructions are not followed; but making the instructions more complicated and specifying them in more detail reduces the price of failure... at the cost of making them harder to successfully follow.
- It's perfectly possible for her to show up again after your first failure and offer you another set of instructions, or offer them to someone else affected by the trouble you caused, and set things right that way; in fact, for every disaster caused by failing to follow instructions, there is a way for someone to undo it by following another round of advice. However, in order to avoid spirals of increasingly terrible curses as successive people try and fail to fix the last one, she always sets the complexity of a followup solution at a level such that if you fuck it up the trouble you cause will be much less bad than whatever you're trying to fix. This means that followup solutions are really hard to get right, and it might take a while before someone shows up who she believes will be able to handle the cleanup round.
- She can design the solution, but the nature of the disaster is out of her hands. She has a certain amount of indirect influence, and might be able to guess ahead of time what form the trouble will take, but the magic makes its own decisions about how it's going to go wrong, and she can only control it by trying to make sure that the instructions are within your reach.
- Also, the nature of the disaster might partly dictate what kinds of followup solutions she can offer and when; for example, in the case of the Lindworm, she wasn't able to do anything about it until the curse had fully triggered, which means at least one bride needed to get eaten. And then she had to wait for someone affected by the problem to give her an opportunity to offer them advice, and hope they'd be competent to follow it.
- A Mysterious Old Woman can only show up under a fairly narrow set of circumstances. You have to be alone in a place where a kindly stranger could plausibly happen upon you without tresspassing illegally on anyone's clearly marked private property, and visibly upset or worried or concerned or pensive in some way such that it would be at least vaguely reasonable for her to ask you what's wrong. If you are locked in a dungeon, or under close supervision at all times, or never leave the grounds of your enormous and well-guarded castle, the Mysterious Old Woman will be unable to help you no matter how much you need it; and if you take your walk in the woods but spend the whole time whistling a jaunty tune, she can't do anything for you then either.
- There may be one Mysterious Old Woman who can be in multiple places at once, or several Mysterious Old Women all working together, or maybe she just runs a really really tight schedule; no one in-setting knows except the lady or ladies themselves, and she/they is or are not telling. But whatever the details, it is definitely true that the amount of Mysterious attention available at any given moment is ultimately a finite resource. She cannot offer solutions to all possible problems, and so she must prioritize. Generally she will prioritize followup solutions over solutions to fresh not-yet-magical problems, and helping people who need the help especially badly or will use it particularly well over people whose problems are comparatively trivial or who will take her advice and then turn around and make a bunch of other people need it.
- Relatedly, she can't watch 100% of possible advice-seeking locations 100% of the time, and so while it is not very likely that she will just genuinely miss someone looking for her, it's not out of the realm of possibility either. The genuinely desperate are best advised to keep trying even if their first couple of walks in the woods or lingering stays on out-of-the-way park benches don't pan out.
- Except under extraordinary circumstances, she can't actually tell you what the solution is going to be before you implement it. You just have to trust that she knows what she's doing.
- The MOW is wise and knowledgeable but not a literal oracle; she'll have a really good guess about what you want from her before she appears, but she might be wrong. And once she shows up and listens to your problems, she has to offer you a solution, even if the problem you ask her to solve is one she doesn't have a good solution for, or doesn't want to solve at all. The latter sort of situation generally ends in her giving you a ridiculously difficult set of instructions and a comparatively low-magic solution and hoping that you eat four instead of five sunflower seeds on the sixth day of preparations and turn your hair and fingernails permanently grass-green; in the former, well, she does her best.
The MOW generally tries to aim for instructions that are about as complicated as she judges you can handle, within safety margins dictated by the amount of magic necessary to solve your problem. If alleviating your worries would take enough magic that she'd have to give you a 50-page manual in order to get the magnitude of the disaster below world-shaking proportions, she will almost certainly not even show up. If you're a candidate for implementing a followup solution but she doesn't think you can handle the required complexity, she probably won't show up for that either, although she might take a chance on it if things are going badly and it doesn't look like another candidate will come along anytime soon.
Examples of the sort of thing a MOW can give you include: various fertility solutions (magic pregnancy roses, creating a child out of a log, hatching magic eggs into babies), healing of illness or injury, rescue from abusive or otherwise harmful life situations, mysteriously appearing piles of treasure, uncommon luck at crucial moments, small helpful magical items (a cap of invisibility, a pair of seven-league boots), and sometimes more extensive and long- or at least medium-term assistance (e.g. there's a Mysterious thread where a MOW puts together a Cinderella setup for a Libby whose problems are approximately Cinderella-shaped).
It is usually pretty easy to tell that you're looking at a proper Mysterious Old Woman and not a mere ordinary helpful elder. She will usually have some detectable sign of magic about her, such as strange lighting effects, a lack of footprints where she really ought to have left some, a face that's never the same between any two instances of looking at it, clothing that moves according to air currents that are not the ones actually present, or stronger hints of insubstantiality such as her skirt or walking stick visibly passing through a solid object. No single sign is universal: any given MOW might leave footprints, or behave normally with respect to air and light, or bump against environmental obstacles in an ordinary mortal fashion. But there's always something.
Nevertheless, it is possible for an ambitious person to attempt MOW impersonation. It is not advised. Don't do it. The very best you can hope for is that you will get away with it once; further attempts may lead to consequences, and the consequences may involve terrifying curses, which will almost certainly land on you instead of or in addition to the people you trick into following your faux-magical advice.
