This review contains spoilers. Iron Lung earns its ending and the ending requires discussion.

The premise is this: most of humanity has vanished in an event called the Quiet Rapture. Stars, planets, most people, gone. Only those on space stations and ships remain. A blood ocean covers a desolate moon. A convict named Simon is forced into a welded-shut submarine, sent down to photograph and collect samples from the bottom of that blood ocean, and told that completing the mission will earn him his freedom. He cannot see out directly. He can only take still images through a camera he later learns is an x-ray device that has been slowly irradiating the crew outside.

This setup is borrowed from David Szymanski's 2022 indie horror game, which Markiplier played on his YouTube channel and fell in love with. The game is minimalist to an extreme: you are alone, you cannot see out, and something is clearly out there. Markiplier's film expands the premise into 125 minutes of slow-burn dread with a genuine character arc at its center, a man who deserves nothing discovering that he has something worth dying for.

The business story around Iron Lung is as remarkable as the film itself. Mark Fischbach, a YouTube gaming personality with 35 million subscribers, self-financed a $3 million horror film, wrote it himself, directed it himself, edited it himself, and starred in it. No studio. No development deal. No safety net. The film grossed $48 million. That is a 16x return on investment, achieved outside the traditional Hollywood system, by a creator who simply loved something enough to bet his own money on it. Whatever you think of YouTube culture, that kind of personal accountability and financial courage is worth naming.

The film is genuinely good. Not perfect. Not a masterpiece. The pacing in the middle section tests patience, and viewers unfamiliar with the game's lore may find the mythology underdeveloped. Some of the radio communications are frustratingly vague when clarity would serve the story. But the atmosphere is extraordinary. Philip Roy's cinematography makes the submarine interior feel genuinely suffocating. The sound design creates a pervasive dread that the visual limitations of the submarine setup cannot achieve on their own. And Markiplier, whatever his day job, gives a performance of real emotional texture.

The name 'Quiet Rapture' is not accidental. Szymanski has confirmed the reference to the Christian eschatological event, though the film is not a theological film. It is a film that uses the vocabulary of sudden divine judgment, most of humanity gone in an instant without warning, to create a post-apocalyptic setting defined by complete and permanent loss. What remains is a remnant trying to understand what happened and why. Simon is not a believer. He is a convict, a man who already burned his bridge with civilization by contributing to the destruction of a space station. His encounter with the ocean of blood, with the living thing beneath it, with the audio logs of the men who came before him and died in the same submarine, strips everything away until there is nothing left but the choice of what to do with the last minutes of his life.

He chooses correctly. That is the film's thesis.

The climax, which critics have described as 'a desperate and impressively gruesome sacrifice,' delivers exactly what a film built on claustrophobic dread needs: a release that earns its weight. Simon, now partially merged with the organic material growing inside the submarine, tied to the vessel by biology as well as circumstance, realizes that the black box containing the SM-8 data must reach the surface. Ava, the commander who promised to rescue him, is dead. There is no rescue coming. There is only the data, which may help the last survivors of humanity understand what the blood ocean is and where the Quiet Rapture came from, and there is Simon, who can attach the box to a life vest and implode the submarine to kill the monster and send the data up.

He does this. He dies. The data reaches the surface.

A convict who began the film as a man who took lives ends it as a man who gives his. The moral arithmetic is simple and ancient and Markiplier earns every beat of it. Variety, which called the film 'a sleeper,' noted the sacrifice delivers genuine intensity. It does. It works because the previous 110 minutes have done the quiet, patient work of making you care about a man in a tube.

Conservative viewers should be aware of the content, which is considerable for a PG-13 edge case. This film makes its case for an R rating in several sequences. The body horror in the final act, Simon's skin cracking and blistering as organic matter grows on and into him, is genuinely disturbing. The blood ocean is literal, not metaphorical. The monster is effective. These are not concerns about politics. They are concerns about content.

What Iron Lung is not is ideologically complicated. There is no progressive messaging. No diversity lecture. No institutional critique beyond the specific and justified note that the commanders lied to Simon about being the first pilot. One woman is in authority, and she is shown as competent and ultimately tragic. The ensemble is mixed. Nobody in this film is required to represent anything beyond their character. It is a horror film about a man in a submarine. The man dies to save something beyond himself. He earns his death and makes it matter. That is as traditional a moral structure as cinema offers.

Trope	Category	Location	Authenticity
The Self-Sacrificing Hero	TRADITIONAL	Final act — Simon ties the black box to a life vest, sabotages the submarine, and allows himself to be killed in the implosion so that the data reaches the surface	Authentic. The sacrifice is earned by the preceding 110 minutes and delivered with appropriate weight. No cheap sentimentality.
Redemption Through Courage	TRADITIONAL	Simon's entire arc — a convict who contributed to mass death ends the film dying for the preservation of knowledge that may save humanity	Authentic. The film does not erase Simon's past crimes. It shows him making a different choice when the moment demands it. Traditional moral framework: the worst of us can still choose the best at the end.
Duty Above Self	TRADITIONAL	Climax — Ava asks Simon to protect the data because it may save what remains of humanity; he complies at the cost of his life	Authentic. The film treats this choice as the obvious correct one without editorializing. The character arrives at it through his own development, not because a script told him to.
Consequences of Sin	TRADITIONAL	Simon's backstory and present situation — he is in this submarine because of choices he made; the film treats his imprisonment as the legitimate consequence of real harm he caused	Authentic. The film does not frame Simon as a victim of an unjust system. He did something that put other people in danger. He is serving time. The moral ledger is clear even as the film builds sympathy for him.
Individual Courage in Impossible Circumstances	TRADITIONAL	Throughout — Simon alone, without rescue, without information, without support, keeps making choices and moving forward	Authentic. The film's entire architecture is built around this single traditional value. A man alone. He does not give up.
Eschatological Premise	TRADITIONAL	The Quiet Rapture setting — most of humanity vanished in an instant; survivors are a remnant trying to understand and persist	Organic to the source material. The game creator confirmed the Rapture reference. The film uses eschatological vocabulary without mocking the tradition that generated it.
Truth Must Be Preserved	TRADITIONAL	The black box of the SM-8 data — Simon dies specifically to ensure this data reaches people who can use it; knowledge preservation as a sacred obligation	Authentic. The conflicting voices (preserve the data vs destroy it) frame this as a genuine moral choice. Simon chooses preservation, which is the traditionally correct answer.
Female Authority (Competent)	WOKE	Ava as the mission commander — she gives orders, Simon initially resents them, she turns out to have been dealing with a terrible situation and ultimately dies trying to help him	Borderline. Ava is written as genuinely competent and ultimately sympathetic. The film does not use her authority to make a feminist point. She is just the commander. Standard contemporary casting.
Diverse Ensemble	WOKE	Cast includes Markiplier (half-Korean), several women in significant voice roles, and a diverse supporting ensemble	Organic to the creator's background and to contemporary casting norms. The diversity is present but never the point.