There used to be a lot of arguments on message boards about how this god or that god is more powerful than the rest and whatnot. This is not that.

I am writing an end of the world series of adventures (1-18) where Sigil has crashed and is broken up halfway down the spire. The PCs have to restore, or replace, the multiverse. I want to use as much of the lore of Planescape as possible but am willing to provide my own answers to some of the meta content not revealed. The most important of this is that the creator of the multiverse is the Lady of Pain. Therefore, if you kill/incapacitate the Lady of Pain, the multiverse begins to fall apart as it is unmade.

So, I know that the Lady of Pain is omnipotent, immortal, un-killable, etc. Regardless, I want to weaken/remove her at least temporarily so the multiverse will unravel.

Please help me think outside the box on how to accomplish this. Please do not post how it is impossible, she's too powerful, or similar. Weakening/removing her is the key to my adventure so it doesn't really matter how powerful she is.

My best idea so far: The Dabu are related to the Lady of Pain in some unknown way. Anyone that hurts a Dabu earns immediate retaliation from the Lady. What if she was their goddess? As their goddess, they would have believed her into being. She also refuses to be worshipped as a diety. What if that was because she already was a diety? The more Dabu you kill, or convince not to worship her, the weaker she becomes. What if you managed to turn all of Sigil against the Dabu? She is not dead, simply powerless. Is this too eas a way to get rid of the most powerful being in the multiverse?

Not as good as that one, but...: The Lady is the multiverse. She is able to be so because the doors keep all aspects of the multiverse connected and thus part of a whole. Assume someone was able to convince a bunch of planes to shut themselves off from the multiverse. Would the Lady then begin to fragment? If her personality began to fragment, she would be unable to stop the death spiral of the multiverse. Again, she is not dead, simply fractured and ineffectual. This one would be really hard, but a god, or pantheon of gods, could probably do it.

Last one...: She gets her power from the multiverse. The multiverse is made up of planes which exist because Deities/Petitioners believe they exist. Every mythos has some kind of "end times" where everything is destroyed. What if someone starts those to rolling... If they could kill the 2-3 major deities of each pantheon, would the rest go hide? What would that do to their petitioners? As planes reach their end times, they cease to exist, shrinking the Lady's power. Do enough of this and she begins to fracture again.

Okay, this is the last one, for real...: Someone brings another multiverse into alignment with our own, destroying both. The few places left are places that have no direct correlation between multi-verses. Once both multiverses have destroyed each other, the first being on top of the spire gets to make the new one.

Please assist.

So, first off, in terms of the campaign, why does she have to be defined?

Second, does the reason or rationale have to make sense to the generally insignificant by comparison mortal beings?

Third, note that omnipotent means all powerful, omniscient means all knowing -- the famous conundrum of omnipotence comes into play here, and the only reason it is a conundrum (and not a paradox) is that it interrogates from a mortal perspective.

I ask the above because they are important: What purpose does it solve for the players to have to have an understanding of all of this? All that needs to be known or understood by the beings involved here is that for some reason that lesser being do not understand or comprehend because the Lady of Pain is ineffable, the multiverse is unraveling. Additionally, it is more or less a standard element around her that she remains ineffable, beyond mortal ken, and outside of anyone's ability to grasp.

So, by making it something that isn't known -- and, more importantly, could not be understood or comprehended by mortal beings if it was known (and anything that can die is mortal, even if they can return) -- you will find yourself with the ability to use ALL of those possible meanings because one thing remains true about people throughout the multiverse: they love to speculate.

Thus, you can pepper all of those throughout the whole of the adventure, giving them out, and let the players tell you what they think is most likely by listening to them, not asking them directly. If they hear a bunch of reasons and you make it seem like those reasons are important, your players will slowly make you see what might be the best idea.

Now, if you need to know for your purposes, from a DM perspective, ask yourself how that directly engages the party. Is it just lore that you want to have, or is it just that DMs need to know everything -- because players don't need to know everything. 

If there is some kind of encounter you are planning that is absolutely needed to understand this? IF so, look at the encounter again -- in regular 5e, the most powerful beings that can be slain by PCs are CR30. If the goal is to kill the Lady of Pain in your campaign, then stat her out and let them go for it -- I am not saying that it is impossible or whatnot, what I am saying is that the reason you are seeking is maybe not something you need to have in the first place.

Slaying Gods is something that has been done in D&D since the earliest years, lol. Hell, the Immortals set basically made that a whole thing.

But ime, it is always more interesting and useful to have those Powers That Be in a universe be inscrutable, ineffable, and beyond the ability of people, however heroic, to understand or grasp, both in their persons and motiations, and in their challenges and problems. How does an ant understand the trauma of a three year old?

I have a few ideas involving her mazes. Perhaps she's been trapped in her own maze, or somebody in the maze managed to find its core and destroy it, weakening her hold on Sigil and the multiverse.

@AEDorsay - Your post is really making me think and is extremely useful. I'm getting what you're saying but it does need to be at least partially spelled out so the PCs can run around trying to stop it before it happens. End of the World stories are about what happens right before, and after, the end.

T minus 20:  PC's begin the campaign in Sigil so that they 1) learn how Sigil works, 2) who's who and 3) develop a reason to want to save Sigil. (Lvl 1-3)
T minus 10:  Giant parts of the planes begin breaking off. The PCs try to stop  it via a series of adventures.  (Lvl 4-6)
T: Kaboom:  The event happens. They learn that the tower is a McGuffin and establish themselves at the starting line.  (Lvl 6.5)
T plus 10:     The race starts in a mad dash. (Lvl 7-10)
T plus 20:     The competitors are winnowed down to ten or so and we learn that The Adversary is one of them. (Lvl 10-15)
T plus 30:     The Adversary is revealed as the last competitors are removed. (Lvl 16-17)
T plus 40:     The PCs and the Adversary have their final showdown. (Lvl 18)
Epilogue:      The PCs win, they either use it to reset the status quo or to make their own playground or use it to make a better playground than before. FIN

I kept trying to write out why they needed to know how it's happening and deleting it because "how it happened" has nothing to do with "how they end it." They end it by fighting their way up through a mega-dungeon (the spire) with everyone competing with them to come out on top.

This has been very beneficial. All four of my ideas (and the mazes @Gnomarchy) could work.
1. Dabus are dying: Just killing a bunch of dabus to bring about the end of the world is too easy for the end of the world.
2. Closing doors: Doesn't work because people would come back once they see that cutting themselves off ended the world.
3. Ragnarok, etc: Works really well if I research the End Times of various Outlands planes. I'd have to explain why critical mass built up as destroying them all would be hard.
4. Crashing multiverses: Works really well, especially if I use something like The Shadow Plane. You can't stop it once it begins and it leaves places to stand to watch the world end.

In trying to disprove your statement that it doesn't matter, I've winnowed down what part of it does matter and therefore eliminated two of my ideas. I think I'm going to go with the Crashing multiverses method and say that The Lady of Pain is off somewhere trying to stop all this from happening. That way I don't have to kill/eliminate her at all - bringing me back around to your statement that how you get rid of her only marginally matters.

There could even be a T minus 5 event where someone has to destroy the Shadow Plane's spire so that ours would be usable. Could be a clue that the spire is the McGuffin.

As I said, this has been extremely beneficial to me.

Thank you to you both.

Stealing an idea from the movie Dogma, the Lady has been trapped in a mortal body (perhaps deliberately by a foe). Without her presence, things are starting to unravel.

Also, I really really like that last idea. Multiversal war is such a big concept, it should make for an epic game.

It is like the overarching plot in the computer game Anachronox. In the game, the cyclic universe theory is correct (the idea that each universe expands, then contracts to the Big Bang for the next universe). The plot (sort-of) is that inhabitants of the previous universe are at war with inhabitants of the next universe, and are fighting the way by changing the laws of physics of this universe so that it expands for ever, preventing the creation of the next universe. 

Quote from Samyrmancer777 >>

 

So, I know that the Lady of Pain is omnipotent, immortal, un-killable, etc.

 Is she? Well, not in my interpretation, but never mind that. 

The Cage is famously ... well, the Cage. It's unclear whether it keeps something out, or whether it keeps the Lady in. It's unclear whether she made it, or it's something that was done to her. 

But (and this is my suggestion) the Cage is a responsibility that was offered to her. It is - so to speak - the cockpit of the multiverse. The Lady has taken upon herself the duty of keeping the world running (kinda-sorta smoothly) for the duration of all eternity. She cannot leave - and other players, gods, demons, mages above a certain threshold - cannot enter. So that's it: The cage is the control room of the multiverse. That's why it has portals - service hatches, basically - to everywhere: It's so the staff can make sure everything is running smoothly. 

The staff is the dabus, of course. They're not really sentient, and they're not really people. They're algorithms, given form. 

As with most systems designed to be perfect and run forever, over time sand get's in the gears. Remember Razorvine? Razorvine is the metaphysical sand getting in the gears of the universe, given physical shape. It's ... entropy. Unavoidable, and in a way it's the timer of the multiverse ticking down. The Razorvine is kinda fine in principle, but it destroys what it touches, and if it get's in a portal .... well, then it doesn't destroy just the portal, it destroys what's on the other side of it too. It's fractal, and multiplicative in nature, so as soon as it get's in the first portal, it cascades, become much worse, fast. 

So. What's the real problem? Well, it's this: The Adversary knows that Sigil is the controlroom of the multiverse. It also knows that it - the Adversary - cannot enter the Cage so long as the Cage is doing what it was designed to do, which is keeping players like the Adversary out. So - logic conclusion: Kill the dabus until it stops working. 

And the Adversary, clever though it might be, doesn't know that without a functioning controlroom, the multiverse will quickly fail - it also doesn't know that taking the wheel doesn't make you God. It's more like it makes you the janitor.