Just updated. I've fleshed out much. I have all the Primarchs worked out and will add more as I get time.
Things are still not set in stone, so please feel free to comment on what is here. I am more than open to making changes, whether major or minor, if they are of benefit.
Originally Posted by Original Premise
- Disillusioned and angered by constant run-ins with Guilliman and Dorn, regarding his methods of war. Alpharius perfects his methods, taking them to further extremes – getting better results than ever.
- Eventually Guilliman punished Alpharius for not changing his methods.
- Horus dispatches Lorgar to calm Alpharius, as the Word Bearers had been similarly chastised and had recovered to be productive members of the Imperium.
- Lorgar leads Alpharius further astray, eventually Alpharius to become Chaos’ chosen champion.
- Alpharius arranged Horus to be injured by the Anathame blade.
- Alpharius and Omegon proceed to generate relations with their brothers by undermining others and arousing suspicions and hatred between other Primarchs.
- Eventually Alpharius is defeated and killed; however, Omegon is saved by Tzeench and becomes his servant. Creating the illusion that Alpharius still lives and that he is eternal. Remain Alpha Legion in order to build upon this myth.
- Following the Space Wolves fall into heresy and the release of the Wulfen Curse, mutation within the Imperium becomes feared and loathed.
- Sanguinius, due to his wings, becomes the target of suspicion and hatred, flamed by Alpha Legion’s intelligence forces. He is suspected as a traitor, or at least a sign of great evil.
- During a meeting of the Primarchs (to discuss the aftermath of Russ’ betrayal and Magnus’ imprisonment) Alpharius whispers many things to Kurze. Aided by the powers of Chaos, Kurze’s paranoia overwhelms him and he attacks Sanguinius.
- Sanguinius has his wings ripped from his body and is mutilated by Kurze, resulting in the Black Rage.
- Humiliated, deformed and enraged Sanguinius falls to Khorne.
- Want to give them some love. But not sure how...
- As per canon, considered to be loyal to Hours (as pointed out by both Sanguinius and Guilliman to the Emperor). This holds true, as they refuse to sway.
- When the Wolves succumb to Nurgle and destroy Prospero, the Death Guard follow up.
- Resilient (but not immune) to the poisons the Plague Wolves spread, the Death Guard are the natural choice to combat the Space Wolves.
- Hating the Space Wolves for their vile afflictions and seeing it as a grace the Death Guard earned, rather than sold their souls for, they became great rivals.
- Never corrupted by the Daemon blade.
- However, their bizarre rituals still lead them to strange places.
- When Ferrus Mannus turns to Chaos, Fulgrim refuses to follow.
- During the Drop Site Massacre, Fulgrim witnesses Angron overpower and ready himself to kill Mannus. Fulgrim cannot see his brother killed and intervenes, seriously injuring Angron. Fulgrim is seen as a traitor and has no choice but to switch sides, resulting in a massacre of Loyalist forces.
- Incorruptible as they come, Dorn remains loyal. Minimal changes to canon.
- Defends Guilliman during his period of self doubt and poor performances (due to Omegon’s undermining efforts). Remains steadfastly supportive of the Ultramarines and their Primarch.
- Leads the loyalists in their campaign to stop Alpha Legion, while keeping the fractured loyalist Primarchs together.
- Finds the bodies of the Emperor, Horus and Alpharius.
- The Iron Hands’ need to replace their hands (or otherwise mechanically improve) grows into an obsession.
- The Iron Hands, lead by the Iron Fathers, begin improving the bodies of many Marines, adding mechanical augmentations to already enhanced biologics.
- Close relationship with the Mechanicum, helping create the first Skitarii forces.
- This obsession eventually leads to Slaanesh (resulting in many Mechanicum Skitarii forces also falling to Slaanesh)
- Canon remain largely unchained pre heresy.
- As soon as Alpharius’ rebellion becomes known, Dorn realizes they have been played. Issues between himself and Perturabo were likely an attempt to divide the brothers.
- Dorn goes straight to Perturabo and apologises, admitting his failure and asking his brother to see they were both played. He knows his pride means nothing in the face of the war that is to come, and cannot afford to have Perturabo side with Alpharius.
- Though hatred still remains, Perturabo cannot abide being used and agrees to prove the Iron Warriors are superior warriors, by killing more traitors than the Imperial Fists do.
- Between Dorn and Perturabo they build the greatest defensive structures ever and provide the best possible forces to man them.
- Canon largely unchanged pre Heresy.
- Does not attack Dorn in a crazed rage, instead is twisted into attacking Sanguinius.
- Canon remains largely the same after Heresy, though develops a mutually hateful relationship with the Blood Angels.
- Canon regarding issues with Horus remain the same.
- Caught up in Omegon’s action against Guilliman.
- Omegon arranges for Raven Guard (including Corax) to be overwhelmed due to Ultramarines’ failure to do their job. Corax is saved when Alpharius alters the plan and engages Ork forces, taking massive casualties to save Corax, the Raven Guard and White Scars.
- Corax trusts Alpharius completely, owing his life and believing Alpharius risked everything to save him.
- Corax rages at Guilliman. Guilliman’s refusal to admit his error, leads Corax to knock him out, swearing to never work with the Ultramarines again.
- Enraged further when Dorn refuses to side with him in criticizing Guilliman’s actions.
- During Heresy, Corax sees a chance to get back at Guilliman, and already dislikes Horus and Dorn, so sides with Alpharius.
- Largely unchanged. Though want to give them some more love.
- Present at the drop-site massacre.
Sons of Horus
- The most beloved son of the Emperor and his dedication was unwavering, Chaos could not corrupt him so looked elsewhere.
- Alpharius knew Horus to be the biggest threat. Sent Erebus to steal the Anathame and arrange for Horus to be injured by it, hoping to kill the Warmaster.
- Horus was only injured, but the Chaos infused blade drove him mad.
- Sons of Horus couldn’t risk their Primarch being seen in such a state, given others would want his position.
- Erbeus convinces them to enlist Alpharius help. Alpharius is the most talented strategist and could make decisions that could be passed off as Horus’, giving Horus time to heal. Alpharius would definitely not contact Dorn or Guilliman, the two biggest risks, and had ties only to Horus. Thus he was considered perfect, and his aid enlisted.
- Alpharius began making decisions in the Warmaster’s stead, passing them off as Horus’.
- Ordered Guilliman to take command of the Ork Waaagh! on the Eastern Fringe. When he failed, ordered Alpharius to take command.
- Regained himself after the Heresy became clear. Aided by Dorn, recovered fully and took his place defending the palace.
- Teleported with the Emperor to attack Alpharius. When he came face to face with Alpharius and moved to engage, was stabbed from behind by Omegon (who was still unknown to all but Alpha Legion) and killed.
- Canon pre Prospero remains.
- Thanks to Alpharius’ spy networks, knowledge of Wulfen Curse was known to all the Primarchs.
- As attack on Prospero commenced, Ahriman unleashed “Ahriman’s Reckoning”, a great spell that unleashed the Curse of the Wulfen in all the Space Wolves.
- Those on the ground were paralyzed with pain, swiftly cut down by the Thousand Sons.
- Those not committed to the fight were trapped in the fleet, too animalistic to use the technology, and busy attacking the human crews.
- Russ, overwhelmed by pain, watching his Marines being slaughtered around him, and an ever increasing number of his sons turning into mindless beasts, was approached by Nurgle.
- Nurgle attracted to Wolve’s resilience to pain and the elements, refusing to relent and desire to keep fighting no matter how much damage is inflicted upon them. They are taught from birth to never give in to the hardships and dangers of life.
- Offering a path of vengeance and to have any Wulfen given control of their minds, Russ accepted.
- The Space Wolves regained themselves, the pain of transformation removed and annihilated the Thousand Sons.
- Space Wolves that lose control and become Wulfen (either willingly, or otherwise) become Plague Wolves. Beasts infected with terrible toxins, spreading disease wherever they go.
- Nurgle saw an opportunity to gain control of a power force, while also destroying a force that could end up in Tzeench’s control… double win.
- Fought solo for a long time while Alpharius prepared for action. Fighting against the Death Guard.
- Joined Alpharius when the Heresy came out.
- Early canon remain, regarding Nikea and being the target of Tzeench.
- Magnus confides in Ahriman that the Wolves suffer from the Wulfen Curse.
- After contacting the Emperor, Magnus realizes what he has done and that he was a tool. He refuses to take part and scoffs Tzeench. Prepares his forces to be annihilated.
- Ahriman casts “Ahriman’s Reckoning” and unleashes the Wulfen Curse upon the Wolves.
- Thousand Sons begin carving the Wulfen apart, while those not yet suffering are easy targets without support. Until Wolves turn to Chaos.
- Seeing the Wolves turn to Chaos and the foul beasts they have become Magnus engages. When it becomes apparent they have lost, he flees what little remains of the Thousand Sons.
- Arriving on Terra, Magnus accepts his punishment and is imprisoned, along with his Legion, while the Emperor decides what to do with them.
- During the Siege of Terra, Magnus breaks out and releases his Legion, playing a pivotal role in defeating the Archtraitor and his forces.
- As punishment, Magnus willingly took his place atop the Golden Throne. Forever protecting the remains of the Emperor and allowing the Astronomican to be directed through him (removing the need for the Choir).
- The Thousand Sons were broken down into small teams, working within other Legions (now Chapters), to train and develop their Librarians, as well as providing their potent psychic powers (both on and off the battlefield) to Chapters when needed.
- Canon largely unchanged until pre-heresy.
- Voices disapproval for Alpharius’ manner of waging war. When Alpharius only gets worse (and is clearly challenging Guilliman), Guilliman tells all those with ties, commitments, debts or other loyalty to the Ultramarines to not work with Alpharius, as it is a waste of resources and can be better used elsewhere.
- Ordered by “Horus” to deal with the massive Ork Waaagh! hitting the Eastern Borders. Fails to turn back the Waaagh! and increasingly ineffective in dealing with it. Several defeats sees Alpharius arrive and take command.
- During major offensive in Alpharius’ strategy, Ultramarines leave position after receiving reliable information that the Orks are going to ignore Alpharius’ trap and begin an invasion of Ultramar (intel is false, supplied by Omegon).
- Guilliman’s action almost kill Corax (and cause severe casualties to Raven Guard, White Scar and Alpha Legion forces committed). Knocked out by Corax after a fight.
- Constant, subtle, undermining by Omegon sees Guilliman become less efficient. His tactics and decisions begin getting questioned.
- Self doubt grows within Guilliman, respect from other Legions falls. Only Dorn is completely supportive.
- Leads the Drop Site attack and is massacred, completely shattering his self confidence.
- After the Heresy, Dorn pulls Guilliman together and Guilliman becomes key in keeping the failing Imperium together.
- Pens, Codex Astartes. Implemented much later, largely due to Dorn’s support and belief.
- Early canon remains largely the same (what little there is).
- Never close to his brothers, as he was seen as aloof and untrustworthy (or, at least, unreliable). Particularly Guilliman.
- Developed closer ties with Alpharius because he saw the value in Khan’s abilities and how they could effectively be used.
- Relationship with Alpharius cemented during the Waaagh! invasion on the Eastern Fringe. Similarly, relations with Corax improved, while shattered with Guilliman, who already didn’t have the closest relations with Khan.
- Largely the same Canon.
- Dispatched by Horus to bring Alpharius back into the fold. Instead leads Alpharius completely off the rails.
- Angron was seen as an easy target for Alpharius. His rage issues, coupled with long standing issues with the Emperor (and general distaste for most of his brothers) made switching him easy.
- However, Alpharius saw him as a weak ally, offering little to Alpharius’ methods and who would have insubordination issues.
- Alpharius deliberately left Angron alone, hoping to take advantage of his obvious flaws.
- Present at the Drop Site Massacre. As Angron was about to kill Ferrus Mannus, he was attacked by Fulgrim and severely injured.
This section is more detailed, but still not put into proper writing or anything. It is just the ideas as they get more fleshed out, as the above it just the skeleton still.
The First Heretic
Lorgar spread faith and worship of the Emperor as a divine being, going against his father’s vision of uniting the galaxy in secular truth. As punishment for this great sin the Emperor made Lorgar and the Word Bearers Legion watch as Roboute Guilliman raze the city of Monarchia (the capital of Khur, a planet of significance to the Word Bearers) as punishment for his actions.
Lorgar was lost without his faith, unable to know what path to follow when all his beliefs had been shattered. In this moment of uncertainty Lorgar was vulnerable to the whispers of Chaos. Lorgar, encouraged by his most trusted, and already corrupt, advisors Erebus and Kor Phaeron fell into the service of the Chaos Gods.
Alpharius was the last of the Emperor’s progeny to be found, placing him at a disadvantage with his brothers. He had neither the relationships the others had developed over decades and centuries, nor the respect that could only be earned through battle. To counterbalance this weakness, Alpharius put great effort into establishing the most comprehensive and effective intelligence network within the Imperium. Spies, informants, information brokers, intelligence officers and much more became entwined in a vast web of knowledge, secrets and intelligence.
Alpharius always knew his enemies, as well as his friends, allowing the most effective methods to achieve goals. Reliable intelligence allowed surgical strikes at key locations; operatives sabotaged enemy positions; assassinations removed key personnel; uprisings were incited. Martial force was but one tool in Alpharius’ arsenal.
It didn’t take long for deals to be struck with powerful Houses of Assassins. Alpharius used his influence and resources to empower the various Houses, who in turn pledged their allegiance to him.
Both Rogal Dorn and Roboute Guilliman looked upon Alpharius’ methods with disapproval. Dorn felt the underhanded methods employed by the Alpha Legion were cowardly and unclean, while Guilliman believed them to be inefficient and out of line with his own methods. Alpharius had heated arguments with both Guilliman and Dorn on numerous occasions, resulting in bitter relationships with both Legions.
The most combustive argument occurred when Guilliman question Alpharius’ approach to war, pointing to his own Legion’s record.
Alpharius took his methods forward, pushing his Legion harder and harder. The Legion took on more powerful enemies in increasingly more dangerous situations, forcing his Legion to grow as warriors and putting greater reliance on their flexibility and ability to incorporate multi-faceted warfare. Splitting his Legion further allowed Alpha Legion to operate in more theatres of war, as less manpower was needed with Alpharius deliberately handicapping his own forces.
Guilliman became ever more irate at Alpharius., enraged at his attitude and conduct, believing Alpharius to be “little more than a disrespectful child”. The meeting ended in blows and Alpharius storming out.
In response, Guilliman declared that all elements of the Imperium loyal to him would no longer work alongside Alpharius, as he considered it too great a waste of time and resources. The Ultramarines had 2 centuries of relationships and history that Alpha Legion couldn’t match, so Guilliman’s ties were extensive. This resulted in numerous elements of Alpharius’ fleet leaving or simply refusing to do their job. With elements of the Legion is entrenched and/or isolated the breakdown proved disastrous. Alpha Legion forces went un-reinforced and lacked resources, resulting in considerable casualties and the loss of much of the work Alpha Legion had done, as they were forced to withdraw toward Imperial space. Enraged by this act Alpharius gathered his Legion, replaced those who had left on Guilliman’s command and again pushed further into uncharted space, laying waste to all those encountered as he and the Alpha Legion took out their anger on any enemy that presented themselves.
Concerned for his brother, Horus could not stand by and allow Alpharius to become dangerous isolated in his relationships. He dispatched Lorgar and the Word Bearers to Alpharius’ side. Horus knew Lorgar had been through similarly tough times, but had overcome such censure and grown into the role expected of him.
Instead Lorgar took Alpharius further away, bonding with the youngest Primarch over their mutual hatred for Guilliman and the Ultramarines. Lorgar subtly encouraged the seeds of anger, resentment and despair within Alpharius, turning him into a bitter and twisted man. Soon Alpharius pledge himself to Chaos, becoming the champion of the Dark Gods.
Horus could never be turned, Alpharius knew this. Horus had been the prime target of Chaos; however, his loyalty and devotedness was unassailable. With this failure Chaos had turned to the master strategist, one whose schemes and strategies could achieve what Horus would have done with charisma and power.
Now it was left for Alpharius to remove the threat Horus provided.
Dispatching Erebus to Horus’ fleet, it was ensured that a vile blade of Chaos, the Anathame, fell into the hands of Horus’ enemies. Horus was positioned so that an ambush was sprung and the Warmaster struck by the tainted blade.
Alpharius’ plan did not succeed and Horus survived. However, the taint of Chaos, warped Horus’ mind, driving him mad. The Sons of Horus could not risk word of Horus’ condition getting out, as others would surely claim the Warmaster’s title. Horus would not be trusted again.
On Lorgar’s advice Alpharius was called. Alpharius was the only Primarch that could be trusted. He possessed ties only with Horus and he definitely would not talk to the Primarch’s whose opinions were most feared, Dorn and Guilliman. Furthermore, Alpharius possessed the strategic decision making required for such decisions to be passed of as Horus’. For the time being, Alpharius would make decisions in Horus’ stead, allowing Hours time to recover.
The Secret War
Alpharius knew he did not have the relationships required to attract more of his brothers to his side, instead he would have to work to create reasons for defections. He saw an opportunity to both breakdown the loyalty of some Legions, while also undermining his most hated brother.
Alpharius dispatched Omegon into the Ork dominated territories beyond the Eastern Fringe. Plunging deep into the Ork Empires, Omegon and a small force of hand picked operatives (both Alpha Legion and human) began the wheels turning on a vast scheme to undermine Guilliman and severe his ties with fellow Legions.
Omegon picked the most dangerous of the Warbosses in the region, Gizbot Skull Krusha, and marked him for ascension to greatness. Omegon engineered wars between the various Tribez with a vast array of schemes. They raided key Ork facilities, leaving behind evidence that the raids were carried out by rivals. The Alpha Legion gave the various weapons and materials they had stolen during raids to other Tribez in exchange for attacking their neighbours. Soon the entire sector was engulfed in Orkish warfare. Assassinations of Warbosses were carried out, ensuring the quick ascension of Gizbot from Warboss into Overlord of the numerous Tribez and Empires. The result was a massive Waaagh! that crashed into the Imperial Eastern Fringe.
In response to the most massive Ork incursion ever seen, Guilliman and his Ultramarines sallied forth, as did forces from the Emperor’s Children, Raven Guard and Alpha Legion. Guilliman dismissed the need for the Alpha Legion forces; however, Horus had been insistent. The Alpha Legion was the only other force with significant numbers in the area and thus they were needed to protect the Imperium. Guilliman grudgingly accepted this.
Omegon used compromised Ultramarine intelligence networks to feed false information to Guilliman. Never enough to arouse suspicion, yet just enough to reduce his efficiency. Guilliman was succeeding in combating the Waaagh!, though he was increasingly less effective in doing so. As the war raged Omegon began feeding more and more intelligence to the Orks, allowing them to respond to Guilliman’s action with great efficiency. Coupled with feeding increasingly erratic intelligence and subtly sabotaging plan, Guilliman soon began to lose control of the war.
Alpharius and Corax arrived, brining with them significant re-enforcements. By the Warmaster’s order Alpharius was to take command as the Ork numbers were beginning to swell, threatening to overrun the Eastern Fringe. Thanks to extensive intelligence and the substantial work of his operatives Alpharius’ command was perfect and the Orks were forced back on every front and soon the Waaagh! had been halted.
Guilliman was unhappy with the methods used, and his attitude toward Alpharius was venomous. However, Corax found the methods brilliant. The Raven Guard’s own attitude of hit and run, precision strikes and flexibility fitted Alpharius’ plans perfectly. Corax held Alpharius with newfound respect, while questioning Guilliman’s attitude toward him.
A crucial battle, aimed at breaking the back of the Waaagh! was set to take place. Corax and his Raven Guard, along with the Emperor’s Children, would draw the Orks into an engagement. While support from the Ultramarines and Alpha Legion would come once underway.
Shortly before the battle commenced, Guilliman received intelligence from a reliable source that Ultramar was to be attacked by a massive force of Orks, who were set to ignore Alpharius’ trap and raze Ultramar instead. Unable to contact Alpharius and with time running out, Guilliman withdrew the vast majority of his forces and moved to protect his worlds.
The attack came, just as Alpharius expected, and the Raven Guard and Emperor’s Children were being overrun. Without Ultramarine support the Imperial forces were being annihilated. With the plan broken down, thanks to Guillimans actions, Alpharius was forced to adjust. The Alpha Legion threw themselves into the battle, taking the majority of the focus, while allowing the Raven Guard and Emperor’s Children to regroup and re-engage. Alpharius’ quick actions saved his brother Legion’s forces, but cost his own dearly. Victory was achieved but Alpha Legion took the most significant casualties.
Meanwhile a minor Ork fleet entered Ultramarine space. It was small enough that the local defenses would easily have dealt with the threat.
Corax was enraged, accusing Guilliman of jealousy and deliberately trying to undermine Alpharius. He insisted Guilliman was more than happy to sacrifice anything, including Corax’s life, to get at Alpharius. Guilliman insisted that he had acted in the best interest of the Imperium, with the intelligence he had, his reaction just justified. Corax laughed at Guilliman’s record over the campaign and said Guilliman cared only for Ultramar, not for the Imperium. A fight broke out between the two, ending with Guilliman unconscious and Corax swearing to never work alongside the Ultramarines again.
Corax’s opinion of Alpharius was absolute, he had seen Alpharius throw himself and his Legion into battle in order to save his allies, willingly taking his own losses for the greater good. Furthermore, his command had been exquisite.
Much is the same as in the original... though a few changes are about.
Horus has been promoted to Warmaster.
Lorgar is the first of the Primarchs to be corrupted after being told to stop worshiping the Emperor.
Alpharius was the last discovered and retains close ties only with Horus.
Horus was the first choice of Chaos; however, he way too loyal to be corrupted, thus a new target was needed (as such Erebus does NOT arrange for Horus to be injured by the anathame)
Alpha Legion has an growing spy network, though it is still young and relatively small, as the Legion has not existed for long.
After being criticised by Guilliman for his approach to warfare and being told to look to Gulliman's history and successes Alpharius is angered and pushed his Legion harder than ever (exactly as before). Alpharius plans the "perfect" tactical attack Tesstra Prime (exactly as is) and received censure from many of his brothers. Alpharius is embittered by this, particularly Guiliman's chastising, and becomes furious.
This is Chaos' chance. Alpharius is the youngest of the Primarchs and thus holds the least ties to the Emperor. He is eager to prove himself and his Legion's tactical and strategic dominance. He is angry at and holds little care for many of his brothers, particularly Guilliman and Dorn.
Chaos takes this opportunity to influence Alpharius and dispatches an already corrupred Lorgar (and/or Erebus) to truly corrupt him.
Alpharius fall much easier than Horus did, not needing the anathame injury Horus sustained.
Alpha Legion invests heavily in growing and developing its network of spies, infiltrators and operatives. Alpharius wants to know everything he can, while also being in a position to alter the information his enemies (and potential enemies) are receiving.
There are two key targets Alpharius has to deal with:
- Horus. As Warmaster and loyal subject to the Emperor he cannot be turned.
- Guilliman. Both to prove Alpharius' superiority, as well as dealing with the greatest tactician & strategist threat that the Imperium possesses.
To deal with Horus, Alpharius arranges for Erebus to sabotage Horus' campaign against the Interex, providing them with the anathme sword with which to injure Horus. Though he cannot be turned, this weakens Horus mind and causes him to become unstable. His action become more erratic, quicker to anger, etc. In this state he takes to listening to Alpharius' guidance more, as Horus believes him to be the greatest General alive.
Guilliman take much more subtly to deal with, as Alpharius wants to use him to gain allies.
Alpharius engages in a massive spy/infiltration campaign against the Ultra Marines. He ensures they receive SLIGHTLY incorrect information from time to time. It is important that the changes are minor, as he does not want to tip anyone off. He also ensures the enemy receive (or stumble upon) information of the Ultramarines, allowing them to perform better against the Ultramarines. It is always ensured that the Ultramarines win; however, they are not as efficient as they should be. This gets noticed over time. Guilliman's stocks drop slightly.
Meanwhile Alpharius sends operative deep into uncontrolled space, where they arrange the ascendancy of one Ork Warboss. He begins to dominate the local tribez and Waaagh!'s toward Imperial space. The operatives ensure all potential rivals fall quickly to this boss, making him incredibly strong. A force consisting of sections of the Ultramarines, Raven Guard, Emperor's Children and Alpha Legion are sent to deal with this Waaagh (as it is now truly huge). Alpharius uses his sway over Horus to be granted command, this is accepted by the Raven Guard and Emperor's Children as Guilliman's recent performances don't inspire them with confidence.
The campaign goes smoothly (Corax and the Raven Guard perfectly complementing Alpha Legion's methods. As does Fulgrim with the beauty and grace of Alpharius' movements and methods) and Alpharius perfectly picks apart the Waaagh! with minimal casualties to any of the Legions. Just prior to a major battle Alpharius ensures Guilliman receives intelligence that proves the upcoming attack will fail miserably. He acts at the last minute, breaking Alpharius' plan. Being false information, there was no danger, instead Guilliman's actions cause massive casualties to the Raven Guard and Emperor's Children in which Corax is almost killed and many of his senior commanders are killed.
Corax and Fulgrim are furious with Guilliman, accusing him of acting to undermine Alpharius and out of jealousy. Gulliman's pride has been strained considerably recently and this pushes him to the limit, he accuses Corax of cowards tactics (being hit and run, infiltration, etc) and the pair almost come to blows. Now Corax holds issue with both Guilliman and Horus.
Fulgrim is similarly disgusted.
This is not in any chronological order, I'm just putting in how I see the other Legions playing out.
Space Wolves vs Thousand Sons
Magnus has has his hand guided by Tzeench, just as in the Horus Heresy series. He is the target of Tzeench and is desired to be the Changer of Ways' new, powerful toy.
With Magnus forseeing Alpharius' fall he attempts to warn the Emperor, as per original. The Wolves are sent to bring them in and Alpharius ensure Horus orders them destroyed.
Alpharius' spy network has ensured the Thousand Sons have prior knowledge of the Space Wolves' secret, the Cure of the Wulfen. With the right push, the Thousand Sons begin working on a spell that will ravage the Wolves, affecting them all with the curse.
The Space Wolves begin their attack and they begin the beat down on the much smaller Thousand Sons. The Thousand Sons situation looks precarious when Ahriman and Co unleash their spell. The Wolves are struck down, their bodies deforming and their minds beginning to be lost, as they turn to mindless, vicious Wulfen. Desperate for aid Russ is opened to any alternate option, and their is one logical caller... Nurgle. Taking the chance to undermine his hated rival, while empowering the forces of Chaos with the deadly Space Wolves, the Grandfather whispers to Russ and offers him salvation. The Wolves will be saved from the curse, they will be stronger than ever and they can strike back against the enemy who would stoop to such disgraceful measures to combat them.
Russ agrees and the curse halts. Many of the Space Wolves are already Wurgen; however, they retain their minds. Their bodies are now tougher than ever, enhanced by their transformation. Those that have become Wurgen are "blessed" further with the diseases and pestilence of their new master. Their physical state makes them immune to the effects themselves, and they become the perfect hosts for these corruptions. Half wolf, half man, disease plagued and angry. Boo ya.
The Wolves fall upon the Thousand Sons and annihilate them. Magnus is broken by Russ and ripped apart by his Wurgen. Only a few Thousand Sons escape. Their loyalty to the Emperor is renewed in the face of the abomination they faced. Their sins forgiven as they were proved right. They go on to individually, or in small groups, join the other loyalist Legions (and eventually Chapters) to train their Librarians and to help empower the psychic users within the Imperium. They are also called upon by Chapters when they need more psychic power to bolster their forces. They are too small to ever form their own force, instead being a supporting role among the others.
The Suspicion of Sanguinius
After the corruption of the Space Wolves, there is great concern about the dangers of mutation. Sanguinius' wings are a visible sign of mutation, something his brothers would come to hold against him. With some well chosen words Lorgar and Alpharius are able to isolate Sanguinius enough. Dorn, who is adamant about doing things the "right" way, being "clean" and "proper" is the most outspoken regarding concerns with Sanguinius.
El'Johnson, concerned with rumblings within his own Legion, is happy to point the finger at Sanguinius also, directing attentions away from his own issues. The Primarchs are divided thanks to Alpharius and Lorgar's dabblings. Alpharius plays on Curze's paranoia and draws him to the conclusion that this mutation is the probable source of his terrible visions. Worked into a rage Curze attacks Sanguinius, beating the Blood Angels Primarch black and blue, ripping the wings from his back and taking mouthfuls of flesh from his body. This action unleashes a rage within Sanguinius, he beats Curze to within inches of his life and awakens the Black Rage within his Legion.
As the other Primarchs discover the brawl they try to pull off the mutilated Sanguinius, but he tries to fight them too.
When Alpharius turns, Khorne uses Sanguinius' rage to ensnare the Blood Angels and take them as his servants.
I will expand on the following.
Angron - too wild and unstable to be trusted. Their methods are easy to read, but their primarch cannot be trusted to not ruin a plan with his "eagerness". As such he doesn't offer much that Alpharius wants. He even sees them as an aspect that can be exploited if he is left to the Emperor.
Corax - After falling out with Guilliman and Horus, as well as believing in Alpharius' methods, they fall.
Curze - easy for Alpharius to manipulate. While he cannot be trusted as he is incredibly unbalanced, he is a useful tool. Alpharius plans to knock of Curze eventually as his instability could be a big danger later on.
Dorn - already hates the Alpha Legion.
El'Johnson - Unsure. They are shifty as it is.
Ferrus Mannus - Growing reliance and love of the augmated. He and his legion are becoming less human. Others are guided to mistrust him, while he is guided to be mistrustful and resentful of others. He seeks to perfect his body further, becoming obssessed with it. This quest delivers him to Slaanesh.
Fulgrim - Ferrus Mannus turns. Fulgrim remains loyal. At the drop site massicre Fulgrim's legion is on the receiving end. During the battle he squares off with Ferrus and cuts off his friend's head. In the rage and upset caused by this action he opens himself to Chaos and that momentary weakness allows him to be corrupted. He then turns on the remaining loyal Legions that dropped to assault the Traitors.
Guilliman - Unshakable. His confidence is shattered, he is used to attract supporters to the traitors.
Horus - Crazed by the anathame blade. Alpharius and Erebus help ensure he becomes unstuck, though he can never be turned. The opportunity is used to get Alpharius (or a key advisor, when Alpharius is busy leading Alpha Legion) close to Horus and advise him. The Alphas make it look benevolent, so Abbadon and Co, are eager for their help so they can try and keep Horus' condition a secret from his brothers (if word ever got out... disaster).
Horus and the Sons of Horus can never be turned, so before starting the Heresy they arrange a situation where Horus is killed (need a how?)
Kahn - Undecided
Magnus. Loyal. But dead. Very dead. Killed by Russ (or should he be left alive to help balance the sides?)
- Loyal (but dead)
Mortarion - After the fall of Russ, the Death Guard are called on to combat the Wolves. Their dedication to resilience has made them the only ones capable of standing up to the plagued Wolves. This enforces their loyalty as they become great rivals of the Wolves. Though their issues with the Imperium are never solved.
Omegon - Horus' doppleganger. After Alpharius is killed by the Emperor, takes control of the Alpha Legion. Under Tzeench's call he takes half of the Legion into the services of Tzeench (the players, manipulators, etc of the Alpha Legion are perfect for this), while the other half refuse to go (instead being lead by Alpharius' Second in Command). The two factions have a great rivalry, seeing the others as disloyal.
Perturabo - Undecided. Despite his issues with Dorn, finds a reason to remain loyal? Why? Why would the Traitors not pick him up immediately as his Legion has an invaluable skill set? Why would he remain loyal?
- Undecided... Loyal??
Russ. He and his Wolves become the servants of Nurgle. Plague Wolves are their new specialist. Space Wolves can willingly undergo the curse of the Wulfen (though for many it is not willing), where they are bestowed with great pestilence.
Sanguinius - Their Blood Rage is exploited. They become Khorn's Chosen.
Vulkan - Unknown
I shall be posting more; however, I am typing it up and it is taking time... please read and comment