Okay, I've been going back and forth on this for a few days, trying to decide whether to share or not, because some of my players may read these forums without my knowledge and thus get access to information they shouldn't have until well into this adventure/campaign idea. But I'll bite the bullet and post it anyway, because I figure if they do read it, I can (a) levy penalties on anyone who metagames, and (b) change it up on them so things go in a totally new direction anyway. That said, when I describe the event around which this adventure/campaign hinges, it should be easy for any players of mine to figure out that it's my game being talked about, and they can just stop reading at that point.
This post is going to be pretty long, so please bear with me and pardon my wordiness.
Now then, the Big Event which forms the seed for this adventure is an upcoming demonic invasion of the Material Plane, which happens on my campaign world every 5000 years, and in the current campaign timeline is now set to occur in about half a year's time. On the appropriate date, a total solar eclipse passes over a specific patch of ground and triggers the opening of a massive portal to the Abyss, appropriately if unimaginatively dubbed the Abyssal Gate, through which demons pour into the Material Plane. Now, this is not a standard portal, because it does more than just create a path between two planes of existence- it actually changes the rules of planar interaction and magic in several critical ways to make the invasion much worse than it would otherwise be. The portal, once open, stays open for 24 hours and then closes again. The eclipse triggers it because of the specific wording of an ancient spell that was designed to shut the portal after it opened for the very first time, so long ago that even the campaign's most powerful gods weren't there to see it; after 24 hours the spell reasserts itself and shuts the portal down again. Without the spell, the portal would stay open permanently, and thus become a much bigger problem.
The problem is a Macro-Large one. In effect, while the portal is open, the Material Plane and Abyss sort of merge into one plane, and Summons actually become Calls instead. In other words, any demon that comes to the Material Plane during that time is truly there in body and not just in spirit, and retains its full suite of powers, even if it was just summoned by another demon or normally loses some power when off its home plane. Demons can't be Banished, because the Material Plane effectively
is their home plane during the time of the portal, and any demons they summon using their ability to do that are actually called instead and thus retain their ability to summon/call others of their kind. Obviously, even one relatively clever demon making it across into the Material world swiftly becomes an exponentially growing problem. The PCs who are aware of this impending doom have been told that on previous occasions of the portal opening, literally millions of demons made it into the Material Plane; on the last portal opening "in excess of two million" came through, and even more are expected to show up this time because the world has been greatly weakened due to the cataclysmic collapse of the ancient civilization that once ruled it (believe it or not, that collapse was entirely separate from the last demonic invasion, which proved to be little more than an annoyance to them at the time).
Many solutions have been tried to stop this periodic invasion from taking place, but all have failed to work- some of the more "out there" solutions included moving the moon to prevent the eclipse from happening on the date in question, performing a massive epic ritual to effectively Dimension Lock the entire world during the time of the portal, and a cabal of powerful spellcasters using up whole suites of Wishes trying to change the wording and effects of the ancient spell that keeps the portal shut during the 5000 years it isn't open. The portal has been opening on this regular schedule, every 5000 years (except when they moved the moon- that actually made it open prematurely), for at least 120,000 years of the campaign world's history. In the modern date, the existing mortals have no idea how to perform any feats on that level of power and effect, so the PCs aware of the Abyssal Gate have no idea how to put a stop to it and save the world. They've even talked about it with one of the campaign's most powerful gods (he likes to show up in person to deal with various issues, and does so fairly often), and from him learned that he's essentially given up hope of stopping the portal from opening and is concentrating on making sure the world survives the coming apocalypse. They also learned another thing from him- the theory that the reason none of the attempts to stop the Abyssal Gate from opening worked is that whatever powers it only exists and can be stopped while the portal is open, thus making sure that whoever might otherwise be in a position to stop it has other things to worry about when the time comes.
That's the backstory, and any of my players reading the above should have figured out even from the way I capitalized Abyssal Gate that it's their game.
Any of you reading this, STOP NOW! I can and will sic Neutronium Golems on all your butts if you acquire information your characters shouldn't have!
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Okay, hopefully they're gone now. If they were ever here to begin with.
In fact, the god's theory is correct- in a manner of speaking. What even he doesn't know is that the Abyssal Gate is not merely a portal or wormhole like other planar portals are, but is in fact the intrusion into the Material Plane by a sentient demiplane that stays quiescent during the time the "portal" is shut. The demiplane itself provides the power to open the portal and change the rules of planar interaction and conjuration, and its motive for creating this link is essentially one of self-preservation. Far back in the dim reaches of prehistory, the mind of this plane learned of a prophecy, which stated that someday in the future, creatures from this particular Material Plane world would kill it. Fearing its impending destruction, the demiplane set out to find a solution, and after millennia of increasingly worried and irrational contemplation decided that the only way to truly solve the problem was to destroy all life on the world in question- thus preventing the rising of the beings from said world who would be able to kill it. Accordingly, it created the special portals between itself and the Abyss and Material Plane, and became the link between them, as well as creating a sort of lure effect that induces demons throughout the Abyss to come to itself and invade the Material Plane once the portals are open. Of course, the irony of the situation is that the plane, by creating these portals and this link to an apocalypse, has given the inhabitants of the world the very motive to destroy it that they otherwise might never have formulated- a classic self-fulfilling prophecy. To permanently stop the portal from opening, the plane must be killed; its mind must be forever destroyed and its power dissipated or the cycle will just start up again in the future.
The intended adventure timeline is as follows: on the day of the Abyssal Gate, the party of PCs will participate in the battle to save the planet, along with several thousand of the world's most elite mortals and even several deities who will show up to help. The invasion gets turned aside in the end, but some of the gods involved notice that something strange has happened with the portal- its closing is different this time and they suspect the closing is permanent. What has happened behind the scenes (though nobody at the time really has any idea of this) is that somebody has succeeded in killing the plane, thus shutting the portal forever.
A few months or years later, when the PCs have become more powerful, they learn that some of the gods have been investigating the Abyssal Gate and determined the cause of the whole mess- i.e. the backstory I explained above. The twist is that their investigations show that the PCs themselves were the ones who shut the portal, so at that point the PCs have to time travel back to the day of the Gate and go fight it.
Now, in ideal circumstances, my intent is to have the PCs fail that first attack, probably by making the plane's mind too powerful for them at the time, and have to live on in a world where the demonic invasion was not turned aside and managed to destroy everything- spend some time gaining levels and trying to help survivors in a post-apocalyptic wasteland, that sort of thing. Eventually the PCs learn some crucial piece of information or gain some critical remaining items or such that will let them try again, and they can contact the world's last remaining chronomancer to go back one more time and set things right. This time, the distraction of fighting two versions of the PCs, combined with the additional power the PCs acquired during their time after the "End," proves to be too much for the plane, and it succumbs- the PCs fulfill the prophecy that started it on the path to ruin so long ago.
The biggest snag in the plan above is that of how to stat up the living plane- how can the PCs fight it, and what precisely do they fight? Originally I was going to use the stats of Azathoth as published in the d20 Call of Cthulhu, and thus the intent would be for the PCs to face it for the final battle some time around the high 40s or 50th level- but the Epic Bestiary combined with the rules for Sidereals has given me a lot more options. And that's a good thing as it happens, because the PC party that's been groomed for this adventure over the years is now around 28th level, with around half a year left before the Gate opens- when my original ideas called for them to be around 30th on the actual day the Abyssal Gate opens (and perhaps high 30s to 40th when they are initially sent back in time to start the first battle against the plane). In other words, they're levelling up faster than I anticipated, so I'm going to need something a lot stronger than Azathoth when the time comes.
U_K, assuming you read through the above, do you have any recommendations for what sort of Sidereal-level monster to use for the plane's mind? Obviously one key snag is that the entity may have Cosmic String and thus be impossible for the PCs to destroy, unless they acquire an artifact that is capable of bypassing that ability (which may provide the reason they need to adventure in the post-apocalyptic wasteland for a while now that I think about it).
In any case, that's my current long-term plan for a slam-bang finish to a truly Epic campaign. There are several key sticking points, particularly in what happens if the PCs TPK or manage to pull out stops I hadn't anticipated and destroy the plane prematurely, but a DM always has to be able to roll with the punches at times like that, so I'll survive. Hope you readers found it interesting and/or inspirational.
