Originally Posted by Malus Darkblade
My Istaavan fluff is not that great but I don't see how Corax was there before the Night Haunter. Even so, Corax only jumped into the fray once shit hit the fan and he realized his men were getting butchered and needed serious help escaping.
All the Primarchs most likely could have survived living on Barbarus and not even Mortatian was able to reach the top of the mountain fortress while the Emperor easily did so.
I don't think Mortarion was special in that he was able to survive poisons and toxins that his brothers could not, rather he just revolved his philosophy around constantly being immersed in a form of death.
He pushed his followers perhaps harder than his brothers in terms of endurance and made them live up to their name as the Death Guard, relentless and unyielding.
Nurgle chose them because Typhos already followed him and yes it is most likely due to the Mortarion being wreathed in poison/toxins all the time. It just fits him story-wise.
As I said, nothing has really been shown that one Primarch was more resilient than the other.
Lorgar had his guts disemboweled by a hot blade which I would wager is a lot more painful and damaging than having a blade stuck in the back or pushed through the stomach. And both the Primarchs were recovering and talking moments after their grievous injuries.
It's all about the willpower of the particular Primarch in question.
The first three legions to combat Horus's forces where the Iron Hands, Salamanders and the Raven Guard. The others had yet to show and where meant to reinforce the three already fighting the Emperor's Children, World Eaters, Death Guard and Sons of Horus. The Iron Warriors, Night Lords, Alpha Legion and Word Bearers all turned on the three loyal legions as they where falling back since they thought they where about to be relieved.
Every Primarch on the Loyalist Side was fighting from the start, Ferrus falling to Daemon Fulgrim's Laer Blade, Vulkan smashing anything they came near him, and Corax swooping from place to place where he was needed literally cutting marines in half with wings that where attached to his jet pack.
When they realised they where betrayed Corax ended up decending upon the Gal Vorbak, the elite possessed of the Word Bearers, Lorgar who despite calls from his adopted father Kor Phaeron and Erebus tried to save what he could, using a psychic power he "buffed" himself and all his Word Bearers, however despite landing a pretty hefty blow against Corax with a weapon made for him by Ferrus Manus, was nearly gutted by Corax's power claw, just as Corax was about to finish him, Night Haunter decided to intervene by grabbing Corax's arm with a grin on his face. The "little Raven" decided to escape and used up his remaining fuel to pull free and fly off.
Anyway as you can see, Corax had been fighting for ages before the "reinforcements" arrived, he then had to turn and confront this new enemy as well as the Primarchs.
Corax is a pretty bad ass Primarch, afaik
he's one of three to beat Horus in a duel as well as stick two fingers up at him when they got into a fight.
If you read First Heretic, A Raven's Flight and the Face of Treachery in Age of Darkness, it'll give you the whole picture of what happened to the Raven Guard during the massacre, you can even throw in Fulgrim to give you more detail on what happened around them, like the fight between Ferrus Manus and Fulgrim.
I'll agree to disagree on the Mortarion subject, I believe he had unnatural resilience beyond other Primarchs, just as Vulkan is actually supposedly the "strongest" of the Primarchs now or Guilliman was the best tactician etc.