Horus

Yul Brynner Lex Luthor Jean-Luc Picard Professor X pre-paralysis Vin Diesel Horus Lupercal, the Warmaster. Here shown prior to getting his Chaos on.

"Let the galaxy burn."

– Horus Lupercal, ruining everything for everyone for ever

"Better to reign in Hell than to serve in Heaven."

– Satan in John Milton's Paradise Lost.

"Angels are bright still, though the brightest fell."

– William Shakespeare

Horus *wah Daddy, I didn’t get enough hugs* Lupercal, The Breaker of Tyrants, The Warmaster, The Arch-Traitor, That Bald Cunt, Horace Heresy or FUCKING HORUS! was the Primarch of the Luna Wolves/Sons of Horus/Black Legion, and the main figure in the event known as the Horus Heresy (this is NOT a dead giveaway. Oh no), who is generally known as "THE GUY WHO FUCK'D IT ALL UP", but not really really.

Overview

Young Horus in all his bald glory (looking weirdly like Benito Mussolini crossed with a WWE wrestler).

Once the most favoured son of his father the God-Emperor of Mankind, he began to resent his father's treatment of him and other Primarchs, and believing that the Emperor's secret plan was to become a god using his own Primarch sons as a tool (when in fact all this is due to the lies of a certain religious zealot), eventually turned to Chaos. If you really need to be told any of this, what in the actual fuck are you doing on /tg/ in the first place? This is such common knowledge, that the outlines of the Horus Heresy and every bad ass taking part in it, are more or less engraved in the mind of every /tg/ reader. Much like the Emperor being crippled and the Imperium devolving into a bureaucratic grimdark empire, the death of Horus and the placement of Abaddon as the most influential Chaos champion ever, turned the Traitor legions from a genocidal force bent on utter domination for the glory of Chaos into a Saturday-morning cartoon villain organization. Also his armour made him look like an egg.

It is argued that Horus was not actually evil but possessed by the Chaos Gods or that he was a victim of Lorgar, who is officially labeled as "The First Heretic." However, he was still a massive dick. Hence the common saying in the post-Heresy Imperium: "Of all the mighty Primarchs, Horus sure was a dick."

But long story short, the Imperium got into this fucked up state because this guy had daddy issues (honestly, who didn't?), he got scammed by religious nutjobs, and because the Chaos Gods showed him horrific visions of the future, supposedly under the Emperor's rule, all while conveniently leaving out the fact that it would be his own efforts to avert said future that would cause it in the first place. Lol-irony. They did show him that the Emperor was planning to discard him and the other rest of the Space Marines when their usefulness ended, and in fairness, that was actually completely true as Master of Mankind shows and which totally contradicts previous Horus Heresy novels where the chambers the primarchs were supposed to live in once the Crusade ended were depicted. Why would you build large apartments for your "sons" if you really did not give a rat's ass about them? Or was the EMPRA intending on luring them into their respective apartment and then strangle them to death? Why go through all the effort when his psychic might was enough to force Lorgar to kneel (causing a small brain hemorrhage as evidenced by blood tricking out of his nose. See "The First Heretic)? He could have just BLAMMED them all Thunder Warrior style with all his psychic prowess and shit. Either way, you know what they say- the best lies contain a grain of truth. The Chaos Gods did show Horus the future he would create which seemed to prove that the EMPRA had planned his own ascension all along (so he obviously must enjoy to be chilling on the couch as a decomposing corpse these days).

It also doesn't help that there's prior precedence provided by Malcador committing damnatio memoriae on the 11th and 2nd Primarchs, a conspiracy which was first uncovered during its development by "Alpharius" and brought to the attention of the Warmaster himself, leading to a confrontation between "Alpharius", Horus, Jaghatai Khan & Malcador the Sigillite on Terra. After calling each other ambitious freeloaders, Horus threatened Malcador's life, to which the Sigillite said if they didn't like the erasure of the recently lost legion, they could shove that precious vainglorious memory of theirs where the sun don't shine. When Horus tried to speak his dead brother's name as an act of defiance, Malcador froze his brain & had to be talked down from sploding his grey matter all over the room by Jaghatai & "Alpharius". When he got back up, Horus flipped a table and gave Malcador the bird when he had his back turned, effectively planting the seed of resentment & pouring boiling piss over it.

It is during this confrontation that it's revealed that Horus had always disagreed with the idea of standard humans ruling over themselves & believed that since it was he, the other Primarchs and their Astartes who conquered the stars, that it should be themselves who rule over the compliant planets; rather than this opinion being implanted by the ruinous powers, it was merely exacerbated. His low opinion on mortals probably isn't helped by the fact that the conspiracy to condemn the memory of his lost brothers was concocted by baseline noble humans (there was even a noble present from House Carpinus by the name of Na-Baron Petronius Vivar at the confrontation with Malcador). Evidently, the other traitor Primarchs thought much the same when he revealed to them that it was the Emperor's plan to give the right to govern these planets to standard humans of noble houses, only to then discard the Primarchs and the remaining 18 legions (2nd and 11th style) once their stated purpose had been fulfilled. How this plan exactly meshes with putting Magnus on the Golden Throne to manage the Webway for Him is unknown, but we suspect it involves strapping an explosive collar around his neck that would detonate should he decide to peel his red ass off the chair. No bathroom breaks.

Either way though, the Emperor psychically nuking of Horus' body and soul means Horus is gone as fuck now, occasional Fabius Bile cloning shenanigans notwithstanding, and Horus' influence of modern 40K will remain posthumous.

Also, 40K(30K?) Horus has more of an reverse connection to his Egyptian god namesake, given the Egyptian Horus heroically took to the throne of the gods from a usurper while 40K Horus is instead the failed usurper.

New fluff

If this reminds you of every Baroque and/or Christianity-related painting from the Renaissance up until the 19th Century, good. Also note how the Custodes are Dark Silver and wearing Pickelhauben (That's because these are Sagittarum Guard).

Recent fluff from the book Vengeful Spirit has Horus visiting the same gate to the Warp on Molech that the Emperor used to get some of his powers. While only seconds pass in the Materium, Horus spends what is basically implied to be an eternity inside the Warp battling rival Daemon Princes, amassing billions of warp-creature minions, and wrecking shit. In the end he somehow gains the same powers that the Emperor received to create the Primarchs, but Horus gets them in a "legit" way (as far as the Ruinous Powers are concerned) by passing their near constant tests through sheer force of will, where the Emperor just took what he wanted. Refusing to become a slave to the Ruinous Powers (or perhaps that's what the Chaos Gods wanted him to think) he leaves his Warp-empire to return to his rebellion in the Materium. Horus' time inside the Warp was so long that he, a fully grown Primarch, had visibly aged. However with his new psychic hack abilities he disguises his over-the-hill face and still maintains his youthful appearance. Apparently the Emperor does the same trick. This was basically a big retcon by Black Library who previously explained Horus being able to fight toe-to-toe with the Big E as having all four Chaos Gods channel their powers into him at once.

It's important to explore this clusterfuck of nonsense to make sense of the lore before one comes to the rubbish conclusion that the Emperor only became god-like after Molech. This is balls-deep nonsense. This is what Horus (who is himself not in any way whatsoever a good source for reliable information regarding Chaos) thinks he knows from his own narrow/skewed/manipulated point of view. The more commonly held belief is that, as with the vision he received from the Great Fuckhead Himself, he was misled. That the Emperor, a being capable of trapping and fighting a C'Tan (that as it turned out had been tired out prior by another warp entity... oops) during the Middle Ages, was always as powerful as He has been portrayed. It is explained that the Primarchs are more than just flesh and bone, and that each of them has a fraction of His personality in them that they themselves embody. Ferrus Manus' rather dramatic death highlights that inside Primarchs lies a great deal of energy. Now to the heart of it - Molech. Why would a being as powerful as the Emperor, who has to combat 4 monstrously powerful otherworldly entities whilst maintaining a beacon anywhere he goes, soul bound psykers and fight throughout the Great Crusade, split His formidable power 20 times into 20 beings? He wouldn't, he'd grab extra power to do so. That was Molech - a source and gateway to a wellspring of power claimed by Chaos for its use alone. A source the Emperor broke into and stole/took/tricked for His Primarch Project. Using the additional power, He crafted, with His scientific mastery, 20 genetically engineered super hosts. In the same way that god-aligned daemons are formed by splitting a portion off the God itself, He used each portion of power as a blank mold, investing them with a sliver of His personality and allowing the power to coalesce around it to form a soul/Emperor-Greater Daemon. That pseudo-daemon is then implanted in a host that can never die or degrade due to age, perfectly tailored to hold it. This explains why each Primarch radiates an aura of awe and magnificence. Horus didn't become as powerful as the Emperor, he retrieved the power that made himself and all his brothers and had it infused into himself. While it appears he has lost a significant chunk of this power (and a piece of his soul) after his duel with Leman Russ in the Battle of Trisolian, the Ruinous Powers soon after began to mainline him with warp energy to the point where he began to bulge at the seams, so by the onset of the Siege of Terra he resembled something in between walking cancerous tumor growth amalgamation and juicing steroid junkie. Whether or not he will manage to be a match for the Emperor as yet remains to be seen. That said, we know who won the duel.

Following the duel with Russ, Horus suddenly entered a near coma, throwing the legion into disarray. Maloghurst later entered the Realm of Chaos and found that a part of Horus's soul - an uncorrupted part - was still trapped in the Warp. That part of his soul was suffering from the effects of Russ's spear, leading to the material Horus falling unconcious. The fragment expressed remorse over it's actions, as well as a morbid clarity that his rebellion was just part of the Gods plan and he had been manipulated into doing so. Left with no other option, Maloghurst destroyed the fragment at the cost of his own life, releasing Horus from his coma and giving him total control over the powers granted by the Chaos Gods, as well as leaving him utterly without doubt in his actions (however delusional they may actually have been).

In Path of Heaven he appears in all his pomp and Chaotic corruption to assign Mortarion to kill Jaghatai Khan, explain that all his other generals have gone doolally and wax lyrical about killing the Emperor, as well as make the point that being 'roided up by the raw stuff of the Empyrean doesn't get you out of having to manage the logistics of a galactic civil war. Soon after, Mortarion kills his Navigators in a fit of rage and makes the dumbass decision to go into the warp anyway. In other words, Horus was the only one of his brothers who had his shit together, which was why the Horus Heresy fell apart so quickly after his death.

Newest fluff heavily suggests that Chaos Gods' plan from the very beginning was for Horus to lose, but only barely. Apparently the Gods knew about the Cabal's plans and made sure they would get the outcome of a fucked up Imperium that lasts for millennia, feeding them with all the negative emotions they needed, rather than an Imperium of Chaos which would go to shit in a few centuries of infighting, taking humanity and gods themselves with it. It does make sense that at least Khorne and Nurgle would appreciate a bloody and decaying Imperium. One daemon even referred to Horus as "sacrificial lamb" needed to stop the Imperium from turning into a prosperous empire of reason, and kickstart the Long War. (Though Eldrad disagrees and John Grammaticus has seen Horus actually won the Heresy and Chaos was not only fine but enjoying the aftermath) The Emperor may have developed a counter-plan that caused the Chaos Gods to scream in frustration in The Outcast Dead but that book is fairly trippy. Later still, Lorgar hinted that the Chaos Gods were displeased with the Warmaster's unwillingness to become a slave to Chaos and that his ultimate defeat in the duel with the Emperor would be a punishment for his refusal to surrender his will to them. By the time of the Siege of Terra, his body and mind were outright falling apart as the Chaos Gods' power was becoming too much to handle, forcing Abaddon to do much of the actual work in leading the Traitor Legions while Horus was either comatose or too insane to form a coherent battle strategy.

Long after the Scouring, Fabius Bile succeeded in creating a stable clone of a pre-Molech Horus, who utterly wrecked a huge boarding party of traitor marines before being fucking impaled through the chest with his own talon by Abbadon. The clone was capable of speech and seemed to possess a semblance of memory from its twin brother's past (calling Abbadon its "son", just before being turned into a kebab). It's unknown why it was so hostile to other Astartes or what degree of control Fabius had over it. Several prominent marines were adamant that such an abomination (cloned Astartes apparently being the closest thing to taboo you can get for even a traitor marine) would not be Horus in any way, because his soul was annihilated by the Emperor.

Good Guy Horus

It's often forgotten by fans that before he was corrupted and decieved by Erebus and Lorgar, Horus was a genuinely nice guy. Fans are quick to joke about "that dick Horus," but before Things Went Wrong he was one of the most personable, down to earth primarchs. Yeah, part of the reason people fell for him so easily was that he shared the Emperor's psychic magnetism, but he also went out of his way to be friendly and considerate of custom, if not necessarily polite. Granted, at times he had arrogance to match Magnus and choler to match Angron, but despite that he always made effort to honor those under his command, mortal and astartes alike. While many primarchs saw their warriors as little more than tools, or were aloof and unapproachable, Horus was a true father to his sons, guiding and shaping them personally. To most legions it would be unimaginable for the primarch to personally seek out and comfort a legionary during a time of crisis, but for the Luna Wolves, it was obvious. He was no saint or coddler, as we see him encourage rivalries within and between his legion and others, but in doing so he brought strength and glory. Even when dealing with outsiders, he always attempted diplomacy before making war, something even his gentler brothers cannot say. In fact, one of the primary reasons why Horus was named Warmaster over other candidates like Guilliman, the Lion, or even Sanguinius was that he was such a people person. He was friends with nearly all of his brothers and was superhumanly savvy when it came to knowing how to talk to people. In this same vein, he was also a master manipulator, and routinely used his savvy to get people, even people who didn't agree with him, to do what he wanted. He was in fact so good at this this he had the ability to change his personality and demeanor to suit particular situations, appearing a slightly different person to others based on what he thought would get him the best results. He got along famously with all of his brothers save one; even total psychos like Angron and Konrad Curze just couldn't help but love the guy. The only brother of his who didn't like him was Corax, which was due to the newly-initiated Warmaster somewhat clumsily trying to exert his authority over Corax and getting a bunch of Raven Guard killed unnecessarily. Horus was a cunning, brutal, supremely confident warlord with a huge cock (what) who nonetheless took great pains to make sure his warriors and mortal retainers were treated well, and furthermore, from the very few pre-Davin POV scenes we get, we know he actually believed others deserved to be treated well, it wasn't simply feigned politeness or a calculated display of regard. Then fucking Erebus happened. Even his edgy rebellion and fall to Chaos was due to his honest love of people. He's basically 40k's version of Arthas Menethil.

Capabilities

It has often been said that Horus was the single greatest of all the Primarchs, and in many respects he genuinely was. Some of his brothers may have had an edge in one particular specialty or another, but Horus was very often among the top 5 in any given category. A jack of all trades, master of most, if you will. As a tactician, only Corax or the Lion were in his league, with the Lion possibly being just slightly better. As a grand strategist, he was akin in skill to Dorn and Guilliman, with Guilliman likely taking the top spot by a small margin. As a logistician, only Perturabo or Guilliman were his match. As a diplomat, only Guilliman, Lorgar, and potentially Magnus were in his league. As a leader of men, only Sanguinius was possessed of similar charisma and nobility. All these traits and more combined to make Horus a virtually unmatched general, one who could fight, plan, improvise, inspire, and negotiate with the absolute best of them. In terms of compliances, he had the single greatest number of military victories under his belt out of all the Primarchs. Only Dorn, the Lion, and Guilliman were close, and only Guilliman had a greater number of total compliances (ones gained through diplomacy or some other non-military means).

There was a flipside to his brilliance, however. While he was arguably the greatest conqueror out of the primarchs, he was not the type of person to leave a planet better than it was before. He had a tendency to destroy and then have legions such as the Ultramarines and Iron Warriors clean up his messes. While he was a magnificent diplomat and always felt that the primarchs should rule humanity, he never actually showed any interest in statesmanship, let alone any ability to rule a world. As a matter of fact, there is no hint that he ever governed a single planet. The primarch who conquered the most planets never stuck around to make something of his gains. He wanted to always be known as his father's favourite and then when he was given the warmaster position he started buckling under the pressure. In other words, he was the classic example of "wanting is better than having".

On the Tabletop

Horus Heresy 1.0

Horus Lupercal, in all his miniature glory.

	Pts	WS	BS	S	T	W	I	A	Ld	Sv
Horus:	500	8	5	7	6	6	6	5+1	10	2+/3++

Horus is everything you love about an HQ wrapped up in one man. He is a very good tactical HQ allowing reserves to outflank, giving every Son of Horus +1 to Leadership and seizing the initiative on a 4+. He and any Terminator unit he has joined may elect which turn they arrive in and they will not scatter if they choose to Deep Strike (and he bestows the rule to the entire unit). He also makes veteran-tactical squads and Justaerin Terminators troops choices (if he is the Warlord... but then again when are you not going to make him your Warlord?).

He is good at shooting with a BS of 5, night vision, a thing that gives - if he chooses to not fire during his turn - a single unit within 6" (other than super-heavy or Independent Characters) +1 BS, a twin-linked super-bolter, and an orbital bombardment using his BS (also twin-linked). And, finally, he is a monster in close combat, being able to take down full terminator squads in 1 turn if you roll well for his 6 attacks plus +D3 attacks if he is fighting a unit or character of weapon skill 4 or lower. He can rape blobs, MEQ's, TEQ's and HQ's.

His weapons are the Warmaster's Talon (an AP2 lightning claw which saddles whoever survives it with a -1 penalty to WS and S for every wound it inflicts that in theory can stack, ensuring that even if he doesn't kill what he's fighting, his target will be completely unable to harm him or anybody else in close combat), and a S10 AP1 master-crafted thunderhammer called Worldbreaker. Combine this with an initiative of 6, and he will strike first most of the time. He's also pretty durable with a toughness and wounds of 6, 2+ armor save, 3+ invulnerable save, 5+ deny the witch, and an additional 3+ save against any psychic attack or adverse profile modifications, which comes to play more often then you may think, given most other Primarchs are bristling with Concussive, Strikedown, Blind or some weirder stat-lowering shit. As in 30k destroyer weapons don't have a "deathblow" result, titan-killer weapons cannot one-shot him, but they still hurt a lot, and while Shadowsword cannot spam D-strength, Magnus definitely can, and the horrible abomination of cheese that is a Warlord-class battle titan could vomit out enough D to kill three Horuses in one turn, so don't get too cocky.

Horus is an absolute motherfucker, and can be thought of as everything a Chapter Master should be between his Orbital Bombardment and army buffs. Letting reserves Outflank makes crossing the board much easier. His Justaerinstar will make anything shit its pants. The Ld bonus patches his Legion's weak morale, and 4+ seize can make a huge difference. His Orbital Bombardment is also awesome. The multi-wound EWless models one finds in 30k will die, and you're likely to put vehicles out of commission. Unfortunately this comes at a really steep fucking price (500 points!) so use him wisely.

Horus Heresy 2.0

	Pts	WS	BS	S	T	W	I	A	Ld	Sv
Horus:	600	8	6	7	7	7	6	6	10	2+/3++
Horus Ascended:	1000	8	6	8	8	8	6	6	10	2+/3++

Horus' already high points cost has risen noticeably, but he has gained some new tools.

• The Serpent's Scales provides the 2+/3++ typical of Primarchs. No additional flashy rules, but he doesn't need them that badly.
• Worldbreaker The heavy hitter for smacking down anything with a bunch of wounds, an AV value, or both. Master-Crafted, S10, AP2, Sunder, Brutal (2), Unwieldy.
• The Talon of Horus: The option for wrecking squads and characters alike. This weapon is S User AP2 and comes with Shred and Deflagrate. Notably it has lost the ability to inflict -1 WS and -1 S on anyone suffering an unsaved Wound from it, and combined with the inability to negatively modify any Primarch's statlines, this has made Horus significantly weaker than before, to the point he loses fights he would've won in the previous edition. That is, unless he supercharges himself as Horus Ascended.
  • The Talon also doubles as Horus' gun. 24" S5 AP3, Assault 3, and Twin-Linked. Again, simple but good enough. It counts as a Bolt weapon for rules purposes.
• He also comes with a Cognis Signum as before to buff his allies' shooting.

As before, Horus also has a number of powerful special rules:

• He shares the Legiones Astartes (Sons of Horus) rule. Which applies to Primarchs this edition.
• Sire of the Sons of Horus: is his unique warlord trait, which grants all infantry models in the same army as Horus +1 Ld and Stubborn. Note that unlike all of the other "Sire of the X" rules, this ignores faction restrictions. As a result, you can use him in a mixed Legion army and they'll all benefit from having him around (as opposed to benefitting only his own Legion like everyone else).
• Master of War: Once per battle, Horus can give his army an extra reaction in all phases of a turn. Make it count, because after that you're stuck with the standard one reaction per phase.
• Master of Weapons: Horus can split his attacks between his weapons, and in the Assault phase he can only be hit in melee on a roll of better than a 4+ regardless of his opponent's WS.
• Deep Strike: Yep, he still works well with Terminators.

Primarchs also have a set of shared rules:

• Independent Character, Eternal Warrior, Fearless, It Will Not Die (5+), Bulky (4) and Relentless.
• They are not affected by negative modifiers to their statlines (other than wounds).
• Resolve snap shots at their normal BS.
• All hits from either shooting or close combat are allocated by the Primarch's controlling player. These hits are kept in a separate wound pool.

Optionally, Horus can be upgraded to Horus Ascended for an extra 400 (!) points, representing his empowerment by Chaos near the end of the Horus Heresy. This grants him a flat boost to his Strength, Toughness and Wounds, the Corrupted unit subtype (which in practice means he gets Fear (1) since its other effects are either already covered or negated by the Primarch rules), Feel No Pain (4+), and Rage (3+). He also gets even more special rules:

• A Dark Fate: The first time Horus Ascended dies, he's instead moved into Reserves with a single wound and can re-enter play like any other model.
• The Power of Chaos Eternal: Once per battle in the Assault Phase, Horus can give himself S10 and T10 for that phase and ignores the Unwieldy rule on Worldbreaker. After that, he takes an automatic Perils of the Warp, whose wounds (if unsaved) must be allocated to friendly models should Horus Ascended be attached to a unit. And why wouldn't he be?
• Spreading Corruption: All models in a unit with the Infantry, Cavalry, or Dreadnought unit types can be upgraded with the Corrupted subtype for 25 points per unit, with all the benefits and drawbacks the subtype entails. Don't forget that Corrupted units can only be joined by Corrupted models.

Horus VS other Primarchs, Horus Heresy 1.0

Horus wins against any other Primarch except Leman Russ and super-charged Magnus. That's it. He beats ALMOST any other opponent he gets pitted against, although it'll take a while with Vulkan.

No seriously, what did you expect? With WS 8, 6 Attacks with a S7 AP2 lightning claw that cripples whoever survives his onslaught or a MC S10 Thunder Hammer and 2+/3++ he can destroy almost any other Primarch relatively safely. He's clearly built to be the hardest dude around and his gear is borderline unfair. Disabling Strike is just disgusting and it's directly intended to make sure he stays the top dog no matter how angry, pretty or well equipped anyone else is... so long as he doesn't piss off the Angel. Ouch, that Talon really hurts. So, yeah, almost no one can actually fight 1 on 1 with the Warmaster, barring some incredibly lucky rolls.

These are the old numbers on Leman Russ pre-FAQ:

• Horus vs. Leman Russ
  • Horus, Round 1: Hits 2 times, wounds 1.777 times with his Claw, 0.888 wounds after saves, and IWND brings it down 0.555
  • Horus Round 2 and on: Hits 1 time, wounds 0.888 times with his Claw, 0.444 after saves and IWND brings it down to 0.111
  • Leman Russ, full Wounds + charge/Counter-Attack (Balenight): hits 4.667 times, wounds 3.502, 1.167 wounds after saves and IWND brings it down to 0.834 at the start of the next turn.
  • Leman Russ, full Wounds + charge/Counter-Attack (Helwinter): hits 4.861 times, wounds 4.051 times, 1.350 wounds after saves and IWND brings it down to 1.017 at the start of the next turn.
  • Leman Russ, full Wounds (Balenight): hits 4 times, wounds 3 times, 1 wound after saves and IWND brings it down to 0.667
  • Leman Russ, full Wounds (Helwinter): hits 4.190 times, wounds 3.492, 1.164 wounds after saves and IWND brings it down to 0.831 at the start of the next turn.
  • Sever Life: Being a pain in the ass to calculate, Sever Life will go off most of the time against Horus, but for the purposes of this mathhammer Sever Life's chance to not go off will be included in its average Wounds roll:
    • Every time Leman Russ Attacks Horus (as he'll always manage to Wound him and it doesn't say it's triggered via unsaved Wounds) Horus takes an additional 1.091 Wounds, only 0.364 of which will make it through Horus' save.
  • Keeping Sever Life in mind and the fact that Leman Russ can split his attacks, the ideal way to split them (for round one and two anyway) would be: 2 Attacks with Balenight, 4/5 Attacks with Helfrost. Here's what that looks like:
    • Leman Russ, full Wounds + charge/Counter-Attack: hits 4.851 times (1.333 times with Balenight, 3.518 times with Helwinter), wounds 5.023 times (1 time with Balenight, 2.932 times with Helwinter, 1.091 times with Sever Life), 1.674 wounds after saves and IWND brings it down to 1.341 wounds at the start of the next turn.
    • Leman Russ, full Wounds: hits 4.177 times (1.333 times with Balenight, 2.844 times with Helwinter), wounds 4.461 times (1 time with Balenight, 2.370 times with Helwinter, 1.091 times with Sever Life), 1.487 wounds after saves and IWND brings it down to 1.154 wounds at the start of the next turn.

Leman's negative to hit modifier is brutal, basically negating Horus' ability to do any damage, while Leman is still pounding him over the head. As stated, this includes Sever Life and Breaker of Shields, Bringer of Ruin. The theoretical breakdown of the match would be:

• Round 1:
  • Leman Russ, 6 Wounds, WS9, S6 + charge/Counter-Attack (2 attacks on Balenight, 5 attacks on Helwinter): hits 4.851 times (1.333 times with Balenight, 3.518 times with Helwinter), wounds 5.023 times (1 time with Balenight, 2.932 times with Helwinter, 1.091 times with Sever Life), 1.674 wounds after saves.
  • Horus, 4.326 Wounds: Hits 2 times, wounds 1.777 times with his Claw, 0.888 wounds after saves.
• Round 2:
  • Leman Russ, 5.112 Wounds, WS9, S6 (2 attacks on Balenight, 4 attacks on Helwinter): hits 4.177 times (1.333 times with Balenight, 2.844 times with Helwinter), wounds 4.461 times (1 time with Balenight, 2.370 times with Helwinter, 1.091 times with Sever Life), 1.487 wounds after saves.
  • Horus, 2.839 Wounds: Hits 1 time, wounds 0.888 times with his Claw, 0.444 wounds after saves.
• Round 3:
  • Leman Russ, 5.001 Wounds (IWND puts him slightly above 5, but it can't regenerate his damaged characteristics), WS8, S5 (3 attacks on Balenight, 3 attacks on Helwinter): hits 3.188 times (1.5 times with Balenight, 1.688 times with Helwinter), wounds 3.498 times (1 time with Balenight, 1.407 times with Helwinter, 1.091 times with Sever Life), 1.166 wounds after saves.
  • Horus, 2.006 Wounds (IWND): Hits 1 time, wounds 0.888 times with his Claw, 0.444 wounds after saves.
• Round 4:
  • Leman Russ, 4.557 Wounds, WS8, S5 (3 attacks on Balenight, 3 attacks on Helwinter): hits 3.188 times (1.5 times with Balenight, 1.688 times with Helwinter), wounds 3.498 times (1 time with Balenight, 1.407 times with Helwinter, 1.091 times with Sever Life), 1.166 wounds after saves.
  • Horus, 0.84 Wounds: Hits 1 time, wounds 0.888 times with his Claw, 0.444 wounds after saves.
• Round 5:
  • Leman Russ, 4.446 Wounds (IWND), WS7, S4 (The Talon of Horus technically causes another unsaved wound here) (all attacks on Helwinter): hits 3.214 times, wounds 1.607 times, 0.536 wounds after saves.
  • Horus, 0.637 Wounds (IWND): Hits 2 time, wounds 1.778 times with his Claw, 0.888 wounds after saves.
• Round 6:
  • Leman Russ, 3.558 Wounds, WS6, S3 (all attacks on Helwinter): hits 3.214 times, wounds 1.071 times, 0.357 wounds after saves.
  • Horus, 0.28 Wounds: Hits 1 time, wounds 0.888 times with his Claw, 0.444 wounds after saves.
• Round 7:
  • Leman Russ, 2.67 Wounds, WS6, S3 (all attacks on Helwinter): hits 3.214 times, wounds 1.071 times, 0.357 wounds after saves.
  • Horus is dead before IWND kicks in for him and so cannot strike back.

Mathematically, if Russ takes full advantage of Breaker of Shields, Bringer of Ruin then Horus loses the fight in 7 rounds (4 game turns!) while Russ still has 2.67 Wounds left. Whoah.

• Do note that IWND messes up the math a little at face value for Talon of Horus. Since Russ does not gain characteristics back that he lost because of Severing Strike, he'll appear to have fewer unsaved Wounds than he actually does.

The above was based on Russ' armour before it got nerfed, which before would make -2 to hits against by round two. Now it is only -1 for the entire battle.

Recalculations from Reddit by u/Fromageopain, showing Horus' win:

• Round 1 (Russ's turn, 7 attacks from charge. If turns are swapped, still 7 from Counter-Attack, but Horus makes IWND first)
  • Russ [6 Wounds, WS9, S6, 2 attacks with Balenight, 5 attacks with Helwinter]
    • Hits 1.333 times with Balenight and 3.912 times with Helwinter, wounds 1 time with Balenight, 3.2601 times with Helwinter and add 1.091 for Sever Life. That leads to 1.7833 wounds after saves.
  • Horus [4.222 Wounds, 6 Talon attacks]
    • Hits 2 times, wound 1.778 times, 0.889 wounds after saves and 0.444 after IWND.
• Round 2 (Horus' turn)
  • Russ [5.444 Wounds, WS9, S6, 2 Balenight 4 Helwinter]
    • Hits 1.333 times with Balenight and 3.201 times with Helwinter, wounds 1 time with Balenight, 2.668 times with Helwinter and add 1.091 for Sever Life. That leads to 1.586 wounds after saves and 1.253 after IWND
  • Horus [2.969 Wounds, 6 Talon]
    • Hits 2 time, wounds 1.778 times, 0.889 wounds after saves.
• Round 3 (Russ' turn)
  • Russ [4.555 Wounds, WS8, S5, 4 Balenight 2 Helwinter]
    • Hits 1.5 times with Balenight and 1.375 times with Helwinter, wounds 1.111 times with Balenight and 1.407 times with Helwinter and add 1.091 for Sever Life. That leads to 1.203 wounds after saves.
  • Horus [1.766 Wounds, 6 Talon]
    • Hits 2 times, wound 1.778 times, 0.889 wounds after saves and 0.444 after IWND.
• Round 4 (Horus' Turn)
  • Russ [4.111 Wounds, WS7, S4 (he is over 4 wounds thanks to IWND, but lost his characteristics since the talon wounded 4 times), 6 Balenight]
    • Hits 3 times , wounds 0.917 times and add 1.091 for Sever Life (let's be kind), 0.669 wounds after saves and 0.335 after IWND.
  • Horus [1.430 Wounds, 5 Talon 1 Worldbreaker]
    • Hits 2.5 times with Talon and 0.75 times with Worldbreaker. wounds 2.222 and 0.625 times. That leads to 1.111 and 0.313 wounds after saves.
• Round 5: (Russ's turn)
  • Russ [2.687 Wounds, WS6, S3, 6 Balenight]
    • Hits 3 times , wounds 0.917 times, add 1.091 with Sever Life (let's be kind again), 0.669 wounds after saves.
  • Horus, [0.761 Wounds, 5 Talon 1 Worldbreaker]
    • Hits 2.5 time with Talon and 0.75 times with Worldbreaker, wounds 2.222 and 0.625 times. That leads to 1.111 and 0.313 wounds after saves. IWND brings this down to 1.09 wounds
• Round 6: (Horus' Turn)
  • Russ [1.596 Wounds (IWND), WS5, S2, 6 attacks on Helwinter (Str2 cannot hurt T6)]
    • Hits 3 times , wounds 0.582 times, 0.194 wounds after saves (not enough to actually kill Horus) and IWND will mean that Horus will actually heal more than Leman inflicts, resulting Horus gaining 0.139 wounds at the end of the turn
  • Horus [0.900 Wounds, 5 Talon 1 Worldbreaker]
    • Hits 2.5 time with Talon and 0.75 times with Worldbreaker, wounds 2.222 and 0.625 times. That leads to 1.111 and 0.313 wounds after saves.
• Round 7: (Russ's turn)
  • Russ [0.172 Wounds, WS4, S1, all attacks on Helwinter]
    • Hits 3 times , wounds 0.582 times, 0.194 wounds after saves.
  • Horus [0.761 Wounds, gain +d3 attacks] and finish Leman...

Keep in mind that these results are made considering that Sever Life will apply regardless of Horus successfully saving the wounds inflicted by Balenight which is greatly benefiting Russ and is probably not the way the rule is supposed to work. On a side note, if Sever Life only triggers when Horus suffers an unsaved wound from Balenight, then the fight is way more one sided in Horus' favor because Leman would have to make more attacks using the sword in order to trigger Sever Life, losing damage since the axe hits harder than the sword.

Take in mind however these above scenerios do not take into account Russ's secret weapon basically designed to counter challenge shenanigans. And even barring that Leman Russ puts up easily the closet fight against Horus on any given day regardless.

The Wolf-kings secret weapon being: Wolves... yeah. Russ can choose to have both his dogs accompany him, both of which are characters. Thanks to how wound allocation and challenges work, Russ can force Horus to engage with the dogs instead of him for 2 whole rounds, making Horus use Worldbreaker to ID the dogs, since if he uses the Talon it'll take 3 wounds total to kill one dog and he can tank the full Worldbreaker on himself to stop the other dog from dying too fast, which prevents his stats from dropping early. As even one extra round of no stat dropping changes everything and by the time his stats even start to drop there is a high probability Horus will be on his last couple wounds if not already dead when the attacks from the wolves are added in to augment Leman Russ. Emperor's Executioner indeed.

Thanks to HH6: Retribution, the Mechanicum has its primarch-like character. Anacharis Scoria, lord of Xana and the first of the Dark Mechanicum used to be able to easily kill Horus thanks to a 3+ Invuln, Feel No Pain, and a weapon that wounds automatically and causes D3 wounds at AP2 per hit (making Horus' talon worthless). This allowed him to kill Horus in 5 rounds, whereas Horus needed 6 to kill him in return. He also got nerfed in the same FAQ that nerfed Russ, so now Horus kills him too.

Gallery

• 

  Ah too many wolves.

• 

  The first Primarch to be fully animated. They coulda made this an actual animated series...

The Primarchs of the Space Marine Legions
Loyalist Corvus Corax - Ferrus Manus - Jaghatai Khan Leman Russ - Lion El'Jonson - Roboute Guilliman Rogal Dorn - Sanguinius - Vulkan
Traitor Alpharius/Omegon - Angron - Fulgrim Horus - Konrad Curze/Night Haunter - Lorgar Magnus the Red - Mortarion - Perturabo