What I actually think was happening during Iron Lung (spoilers)
(Obligatory review: movie rocked, wasn't perfect but it's an awesome cosmic horror movie. Markiplier was a surprisingly great actor, and he turned Iron Lung from a pretty cool but fleeting horror experience into a genuinely meaningful and compelling cosmic horror tale. I hope for a future where he pulls away from YouTube stuff a bit more to devote more time to a potentially successful career as a director.)
So I was talking to some friends and I think I have an idea of what I feel was going on. I posted this somewhere else but here's the Tumblr version lol.
Ultimately I think this is a movie about human perseverence and belief in the greater good overcoming even the most hopeless circumstances. But what's actually happening? Spoilers below:
IMO the radiation stuff, the alcohol, possible concussion, it's all red herrings at best to obscure Simon's visions as nonsense, when in reality it is all the blood, and at most these other factors have just made him more susceptible.
TLDR: A Lovecraftian creature, or God itself, is peering into our world through the Anomaly and erasing everything it cannot see. The blood is a hivemind containing the minds of everyone who's died, as well as the creature. The SM-8 scientist's voice is the woman's mind speaking to Simon through the blood and encouraging him to find the Anomaly before being assimilated into the creature; the creature doesn't want anyone to find out about the Anomaly because destroying it is the only way to stop it.
Everyone has already pointed out that the weird shit begins when blood hits Simon's skin, and I agree that this is responsible for a lot of his visions. We know it's human blood for sure, and that comes with the natural presumption that it's the blood of those who got Raptured. But what about the other supernatural effects of the blood?
I think the blood itself is a hivemind comprising the consciousnesses of who the blood has belonged to and who has died in the blood ocean. At least in the sense of, when Simon hears the SM-8 woman's voice the first time, I believe that is her, or a facsimile of her, talking to him through the blood as part of a hallucination.
That voice is way different from the voices at the end of the movie. The first voice encourages him to find the Anomaly and understand it, while the latter voices are very nihilistic and instead insist that Simon fuck off and die, that the Anomaly cannot be found.
IMO that first voice was closer to that actual person. The second voice was the monster at the source of the ocean. I'll get to that. But I also think the creature(s) Simon sees are likely made of the blood itself. I'm not quite sure how many creatures are actually in the film, I didn't quite get a good enough look to determine if the initial skeleton (which I assume was actually a living creature) VS the creature in the huge tunnel that flees VS the creature Simon kills were all the same or not. But I do think they're made of the blood, based on the fact we know the blood can produce life based on the flora manifesting in the SM-13 in the last act.
But either way I think they're all just the same thing acting through physical vessels: the thing Simon sees in his dream, that huge red eye in the sky.
I think that woman's monologue about God is very telling. Whether this creature is actually God or not is up to you, but I do think it's a very powerful, otherworldly deity. Going by her monologue, about God seeing the universe through a pinhole and struggling to understand it just with that view, I think the Anomaly is the pinhole. I think this God, it somehow found a way to peer into our universe, and either deliberately or just through perceiving us, it erased everything it couldn't see - the planets, the stars. Maybe it really is God, and it has decided in its divine judgment that the universe needs to end. Or it's just an alien thing that inadvertently destroyed whatever it couldn't see through the Anomaly.
(I like to think this creature isn't necessarily deliberately malicious, just acting in its nature. It peered into our world and could only see our manmade space stations, so everything else was erased. Now, all it sees through the Anomaly is blood, so that's all it understands, and maybe it wants everything but the blood to be erased yet again, and is pissed that isn't happening.)
Anyway, I think by doing this, the blood oceans manifest as the consequences of what this thing has killed, and now it is part of them. The thing IMO doesn't have a physical form, it's inside the blood, it is the blood, so the creatures Simon sees are just a byproduct of the blood's nature, congealing and creating monsters that either are just animals, or act as vessels for the God to act through. When Simon sees the vision of that huge red eye, that's the closest he comes to truly seeing it, and that's just a form within the blood, or its mindscape, or whatever.
(Thus, Simon only kills a vessel at the end of the movie, not the actual entity behind all of this. Still a badass move, though.)
Going by this, the vibe I got was the first time Simon speaks to the woman's voice, it feels like maybe that's actually her, breaking free from the hivemind for a minute, or maybe not fully assimilated, to encourage Simon to find the Anomaly - in death, she understands that the creature and its effects can be stopped by destroying/closing the Anomaly, because that is how the creature sees into our world. But when she says Simon's name she's become fully one with the creature, and so now the voice taunts him and tries to get him to give up, because it knows the humans' only hope of stopping it is learning the Anomaly exists and finding a way to close it.
So yeah that's what I think. Ultimately Iron Lung's story is surprisingly optimistic despite the very depressing source material, because to me it feels the ultimate point of the narrative is that humans continue to fight for a better world in spite of hopeless circumstances. The Consolidation of Iron is acting amorally, as has Eden, but this is bigger than Simon. Simon's hopeful monologue about the Quiet Rapture is telling - where he ponders if maybe it's them who disappeared and the rest of humanity is looking for them. I don't think he's right, but it displays the primary theme here, that even with everything going on Simon still clings to hope. In the face of something bigger and more sinister than he can possibly comprehend, Simon ultimately chooses to make his final moments about the greater good.
Ultimately Simon wins, rejecting the crimes the creature and the COI taunt him with, giving humanity hope. Maybe he didn't stop whatever the creature is that's behind this, but he at least gave it a hell of a middle finger before going out with a bang and giving humanity the tools to eventually stop it themselves.