I recently came up with the barebones of a D&D/Pathfinder/etc. setting, but due to various circumstances, I am unable to work on it to any significant degree. As such, I am handing it over to all of you to see what happens.
The premise is as follows, after the creation of a massive, permanent gate to Hell in the southwestern portion of the known land, the good-aligned deities decide to launch a Ragnarok-type event, creating their own permanent gate in the North. Not to be left out, the Abyss creates their own permanent gate in the Southeast. While not the only gates, these three are the main routes through which the forces of the three are sent through.
General reaction of races of the world is for the majority of the good-aligned individuals all going up to join the heavenly host, and the Lawful-Evil and Chaotic-Evil to join up with the side their alignment favors, with half the Neutral-Evil heading down to join either side. The Neutral alignments and the individuals who remained behind take the remnants of world nations and collectively declare war upon all invading forces and those who joined them.
It's not much, but I think you can get a general idea of how things are from it.
I feel like the neutrals would end up summoning shitloads of elementals to fight the angels/demons/devils. Might even have a few carefully watched and kill-switched gates of their own to get the elemental shock troops that much more easily.
Really, though, what this is all asking for is for the planar chaos to end up tearing a rift into the Far Realm.
This is a sort of difficult idea. The players aren't going to start at level one, are they? And what gain would the Devils have from moving the blood war to the prime material plane? Looking at the plot line, it seems like the beings with the most to gain are lawful neutral creatures. You could make modrons or even St Cuthbert the actual antagonists.
A few things. A lot of outsiders have access to greater teleport, which has unlimited range. A simple change (making it so that outsiders don't need to breathe) could mean that 99% of the fighting on the material plane could take place in outer space. Imagine it, the night sky filled with holy fire and the shadow of black lightning. Imagine that you live on an island in the pacific during World War II, and that is the feeling you should be going for. Mortals are completely marginalized. Look up "cargo cults" for inspiration and make that the entire earth.
And it's a losing battle for law. The 9 hells are infinite, but the abyss is an infinite series of infinities. sure, it starts out with succubus and balors, but the flood does not stop or even slow, because at every second an infinite number of demons are coming through the portal. And sure, an overwhelming proportion teleport to space, but the tiny fraction of insane beings of pure chaos stay and corrupt the very ground they walk upon. Worse are the long resting obyrinths, who would devour their weakling tanari cousins and begin trying to break through to the universe before this one existed
Well someone fucked up the math then. Infinity * infinity is much bigger than infinity * 9
Abyss might as well be hell, since it's way more horrifying than the stock description from Dante.
I mean, there's the vanilla type of stupid kind of fuck that joins hell in the first place. But the one that consorts with chthonic and unknowable old ones that grow mouths, tendrils, and whose voices combine into a kind of wordless version of the worst panic attack you've ever had given flesh? That takes a special kind of retard.
Also as a side, Lugonu is OP as fuck.