By all accounts, YouTube celebrity Mark Edward Fischbach (better known as Markiplier) appears to have done the impossible.

Not only did he co-write, direct, edit and star in the first truly successful adaptation of an independent horror game without bowing to any of the major studios, but he also managed to secure worldwide distribution for his passion project by enlisting the fans themselves as part of the flick’s marketing – all the while opening doors for fellow industry outsiders to develop their own “impossible” videogame adaptations.

The best part? The Iron Lung movie actually kicks all kinds of ass, with Mark intuitively understanding the inherent differences between film and video games as unique artistic mediums.

That’s why the adaptation features a series of (mostly) minor discrepancies when compared to the source material, despite the game’s creator, David Szymanski, being heavily involved in the screenwriting process. With that in mind,here are five of the biggest changes that the Iron Lung movie made to the original game and why they improve the viewer experience.

For the purposes of this list, I’ll be focusing on major story elements that actively alter the narrative rather than smaller details like how the titular submarine’s design was altered in order to feel more realistic. That being said, don’t forget to comment below if you think I missed any important changes that you think are worth discussing.

One more thing: major spoilers ahead!

With that out of the way, onto the list.

5. A Bloody Ocean of a Threat

In the original game, the blood ocean served as more of a thematic detail than an immediate threat, especially since the SM-13 vessel operated as if it were in regular seawater once it was submerged. The movie changes this up a bit by exploring why researchers are interested in this inexplicable mass of human blood in the first place, while also depicting the liquid itself as a corrosive and possibly mutagenic substance with a mind of its own.

As the film goes on and blood begins to trickle into the vessel, Simon’s body and the submarine itself are altered in increasingly horrific ways, with the final act leaving our protagonist painfully disfigured – though no less willing to face Eldritch terrors in order to complete his tragic mission.

4. The Siren’s Call

Both the original game’s “Frog” monster and the film’s enormous “Elli” are heavily inspired by real-life Anglerfish, so I found it appropriate that Mark decided to depict the antagonist here as more of a Lovecraftian siren luring explorers to their death through lights and sound rather than a mere animalistic predator.

While it’s entirely possible that Simon is hallucinating his interactions with the beast, he may very well be communicating with a god-like entity linked to the Quiet Rapture itself, which is why I think this was a worthwhile addition to the lore.

3. Radiation Exposure

The Iron Lung game never explained why the submarine’s pictures looked so freaky or how the camera was even operational despite being immersed in literal blood, so it makes sense that Mark would decide to correct this oversight by expanding on the technology behind the device itself while also using it to add extra tension to the story.

In the film, Simon accidentally discovers that he’s actually operating a giant nuclear-powered X-ray machine, with the constant exposure to radiation explaining why the vessel continuously overheats. Radiation might also have something to do with Simon’s altered mental state in the latter half of the experience, an idea that leads into my next favorite change…

2. Carbon Dioxide Poisoning

It’s entirely possible to finish watching Iron Lung and accept its story as a literal sequence of narrative events, but I think it’s far more interesting to take the experience with a grain of salt due to the flick’s repeated hints that Simon is slowly losing his mind due to a combination of radiation and Carbon Dioxide poisoning.

Hell, one could even make the argument that the entire second half of the feature takes place almost entirely within our protagonist’s mind, with this alternate interpretation feeling just as (if not more) impactful as a traditionally literal reading of the script.

1. A Glimmer of Hope

I’ve always been a defender of mean-spirited stories about grimdark futures and existential terrors, but while the original Iron Lung could afford to end on a sour note due to it being a gameplay-focused experience where the players themselves provided character backstory and motivation, the adaptation needed something a bit more concrete in order to turn its bleak finale into a satisfying conclusion.

That’s why I appreciate how Mark and Dave decided to turn the original ending on its head by having Simon defy fate and actually achieve something with his suicide mission despite the source material clearly stating that the SM-13 expedition retrieved nothing of value. While there’s no guarantee that Simon’s heroic efforts will lead to humanity’s salvation, the implication that there’s still hope turns Iron Lung into a humanist parable critiquing the cosmic horror narratives that inspired it.