Hello all. Long time reader, all-too-rare poster, here, looking for some input. Also, my apologies if this is in the wrong forum (can't recall what belongs where... 
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I've had the beginnings of a massive story and/or possible campaign surrounding a major upheaval in Baator (tentatively entitled "The Reckoning: Part Deux") swirling around and fermenting in my head for some time now. While I am an amateur writer (at best), and an even more amateur DM, I have recently been trying to pin down and elaborate on the various motivations that drive the various dukes and archdukes so as to get a better understanding of how they interact with one another, as well as what specific plans they may have in action at the start of the story. Having written out a fair amount on most of the LotN thus far (4-8), I was hoping to get some feedback on what I have so far (plausibility, potential complications, outright errors, ideas, etc.) so that when/if I get around to writing the whole thing out, I will have a more solid foundation to build the overarching plot upon.
For the record, Baator exists largely as depicted in the 3.5e Fiendish Codex II, modified where necessary to conform to earlier Planescape lore (for example, the role and purpose of the Dark Eight). The "death" of Malagarde, the transformation of Malbolge, and the ascension of Glasya as Lord of the Sixth is still quite fresh, though it might be as much as ten years old by this point.
As a starting point (largely because I write most everything on notebook paper first and this is all I have typed up at present), here is what I have for Belial. Questions in bold are things I still haven't fully worked out an answer to (and would be more than happy to hear suggestions on), but feel free to comment on anything and everything.
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Belial
- Belial's consort Naome advised and orchestrated the transfer of power to their daughter Fierna, inspired by Mammon's willful change in form that a self-inflicted punishment might allow her Lord to avoid an even harsher reprimand, such as those suffered by Baalzebul and Moloch, at the hands of Asmodeus himself. Shortly afterward, Naome was slain by an unknown party - Belial suspects on the order of the Lord of the Ninth, as one final censure against him for his part in the Reckoning.
- Prior to the ascension of Glasya as Lord of the Sixth, Belial had been plotting invasions to seize Stygia and Malbolge from their rulers (I seem to recall Hag Countess/Malagarde and Baalzebul had a falling out after the Reckoning. Can anyone confirm?). Afterward, he put said plans on hold to assess the new situation: gathering intel on the new archduchess, determining how an assault against her would be taken by Asmodeus, and so forth, as well as a growing concern over the burgeoning relationship between Glasya and his own daughter, Fierna.
- Seemingly with her new friend's support, Fierna has taken an increasingly active role in baatezu politics and the governing of Phlegethos – areas where previously, despite having nominally held the title of Lord of the Fourth since the Reckoning, she had delegated much authority to her father. Belial fears that she, goaded on by Glasya, may eventually move to oust him and assume full control of Phlegethos herself.
- As such, in recent years Belial has put a large amount of energy into efforts to covertly monitor Fierna's actions and conversations – with moderate success – as well as portray Glasya as a less attractive role model – with little success. Recently secured the cooperation of Chamo, the legate of Abriymoch, to serve as a “spymaster” of sorts, charged with keeping track of Fierna's dealings and reporting them to Belial regularly. (What could Belial offer in exchange? How could he ensure Chamo would remain loyal to him?)
- While still too uncertain to risk moving against Malbolge, Belial has recently renewed his preparations for an invasion into Stygia. (Why? Concern over growing too complacent? Fierna's insistence? Baalzebul? Another factor?)
- Within Phlegethos, Belial counts the dukes Balan and Gaziel as firm allies, but has no official consort – rumors persist, however, that Fierna has assumed that role on many occasions in the past. Among the Lords of the Nine, has maintained a long-term alliance with Baalzebul.
EDIT: Note to self - Rewrite this; figure out how to incorporate Telchur and Vatun.
Levistus and Cryonax have struck up an alliance for an unknown reason. Cryonax has agreed to seek a way to release Levistus from his frozen prison.
In my writings, the reason is elaborated-- the glacier Levistus is trapped in is generated by an uber-powerful (more powerful than the Rod of 7 Parts) artifact-- or to be more specific, a piece of that artifact.
It is one of the 99 (or was it 999?) pieces of the Winter's Ressurection, a super powerful orb used a short time after the end of the Law-Chaos war to tip the Inner Planes back into balance (for a long time the war had resulted in Fire and Earth becoming dominant over Air and Water-- with Air nearly annihilated by Fire, after Imix went on a rampage over the death of Brista Pel, the Princess of Good Fire and his lover. The artifact worked too well and skewed the balanxe towards Air and Water, causing an ice age on multiple prime worlds. However, the power of the artifact was too great for its physical form to contain, and it shattered, spreading across the Inner Planes. Many of the shards have since been procured by various elementals and outsiders, some from the Outer Planes. it should be obvious as to why Cryonax wants to repair and use this artifact.)
I included this in the summary of an Elemental Planes adventure path, where, if the PCs don't prevent Cryonax from gathering all of the shards, Levistus is freed from his prison, which will likely have a major impact on the planes for the next batch of heroes to deal with-- entailing a major upheaval whereupon Levistus seeks revenge and the Lords of the Nine scramble immediately to stop him.
Though not a scheme, in the Timeline topic (titled "was the Law Chaos war" or something like that), I elaborate upon Asmodeus/Aeshma's fall. Essentially, he spent too long in the Abyss (the lower planes are EXTREMELY distressing and uncomfortable for a celestial, as they are cut off from the nurturing essence of their native plane *it's doubly distressing if that lower plane also possesses philosophical *e.g. law-chaos* opposite of the celestial.* During one particular campaign, he spent 66 years uninterrupted there.) Even more significant factors are that many of his superiors, most of whom had never even stepped foot in the Abyss, chastised him for the non-good and evil means he resorted beginning with that campaign in order to annihilate Obyrith. Asmodeus became very frustrated, feeling that his superiors did not understand the degree of evil and the threat that the Obyrith posed.
However, what truly sent him down the path of evil was some of the disturbing events that took place during that 66 year campaign. The Abyssal lords developed a new type of Obyrith which agonizingly parasitized Celestials, feeding off their very essence and eventually devouring their souls (not even a wish can restore them). The monstrosities parasitize their victims by entering the nearest orifice they have access to.
Asmodeus's first encounter with these abominations was when he found his BEST FRIEND parasitized and in agony, begging him for help. His appearance was highly distressing-- his flesh and body possessed a wrinkled, somewhat wasted appearance and his skin had turned a dusky pale gray. In addition, his abdomen was extremely bloated, with several undulating lumps protruding. When Asmodeus tried to heal him, the creature went into death throes and burst forth from his abdomen, killing him, and, at the same time, his body dessicated into a shriveled husk. The dying parasite sprang upon Asmodeus, who quickly dispatched it.
Later on, Asmodeus came upon a horrifying sight-- a brood pit filled with infected celestials, bound to the floor with some sort of sticky mucus or similar exudate. One of them was his LOVER, who appeared to be in agony and a state of advanced parasitization. Similar to the first victim, her abdomen was horribly bloated, but her condition did not appear to be the same. Asmodeus wasn't sure what to do-- by that time he knew that the parasites could not be killed immediately with healing powers, and that any attempt to do so would cause it to burst from the victim's body during its death throes, killing the victim off.
Within minutes, his lover began to scream in utmost agony as her body tensed up; Asmodeus could only watch on helplessly. She.. (this is a bit more graphic than the above) essentially "gave birth" to the parasite as it burst forth from her body, upon which she turned into a dessicated husk. The parasite attacked Asmodeus, and when he was about to kill it, it attempted to catch him off-guard by pleading for mercy using the voice of his dead lover.
In the meantime, several of the parasites were bursting forth from celestials (there were over 100 in that brood pit), and while many of them attacked Asmodeus and his troops, several of them also escaped the pit. Asmodeus was forced to resort to desperate measures in order to ensure that more of these creatures could not escape in order to infect other celestials, and, though less important, out of a glimmer of hope that some remnant of his fellow celestials' soul could be saved. His fellow celestials refused to take such a measure and instead stood ready to slay the parasites as they emerged.
Asmodeus... was forced to slay his own fellow celestials. After that event, Asmodeus swore to wipe out every last Obyrith using any means available to him, no matter how reprehensible-- the Obyrith had to be stopped before more celestials were killed, and before the planes of good could possibly be corrupted or infected... he was also motivated by hatred and vengeance.
As he employed such extreme and reprehensible means, he became more and more corrupted.
This story is the TRUE origin behind the Blood War-- it is not just about law vs. chaos, nor merely about competition for resources. (That said, in my writings, Asmodeus hates the Obyrith far more than he hates the Tanar'ri-- and you KNOW how much he hates the Tanar'ri.)
There is an artifact-- an ancient religious book somewhere in the Multiverse, written by Asmodeus himself long, long ago, that chronicles this story, and from his point of view.