[Note: This review contains spoilers for the video game and some vague references to the movie’s ending.]
“Iron Lung” is a slow-burning sci-fi horror film that takes a long time to get the blood pumping, but delivers a claustrophobic atmosphere with a feeling of isolation and dread that helps keep it afloat. Markiplier’s passion project succeeds in bringing all the original tension of the game to life with an additional burst of bloodshed that has to be seen in all its gory glory.
The universe isn’t going to end in a fiery apocalypse, but rather in the jaws of a creeping silence.
In a future where humanity has set down roots in distant space, all inhabitable planets and stars are inexplicably wiped from existence in an event called the “Quiet Rapture.” Only a handful of space stations are left behind, and the discovery of a moon seemingly covered in a literal ocean of human blood may hold a gruesome shred of hope for the survivors.
In a desperate attempt to find resources and answers, a convict named Simon, played by Mark “Markiplier” Fishbach, is sent into the blood ocean in a rickety submersible aptly nicknamed “The Iron Lung.” With only a low-quality camera to see outside, Simon has to navigate the sea floor almost completely blind. Success will grant him freedom, but soon he wonders if his expedition may be an execution.
The original “Iron Lung” by creator David Syzmanski released in 2022 as a single-player horror game which packed a lot of tension into an hour-long playtime. Gaming YouTuber Markiplier uploaded a playthrough not long after, praising the game’s atmosphere with its “constant and pervasive sense of death” and skyrocketing its popularity.
Markiplier is known for his largely horror-related gaming content as well as his year-long daily video project “Unus Annus” with Ethan “CrankGameplays” Nestor. As of February 2026 he has 38.4 million YouTube subscribers and more than 5,000 uploaded videos, including several choose-your-own-adventure-style interactive series.
Markiplier went on to fund, direct, write and play in the film himself. His portrayal of Simon is raw and devastating, which is surprising to see if you’re already a fan of his usual, relatively lighthearted content.
The game-accurate submarine interior looks cramped and unstable, scored by ominous creaks and groans that you never quite know whether they are coming from the machinery, or something out in the deep.
“Iron Lung” is absolutely not for everyone; there is a good reason the first thing many viewers say after seeing it is that it’s slow. If you find yourself bored or frustrated with horror that takes its time — and this movie takes a LOT of time — then you might want to avoid this film.
The slow ramp-up isn’t unnecessary though. The film uses this time to put you right in Simon’s shoes as desperation to survive sets in. Hours blur together when you’re trapped in a tin can at the bottom of a blood ocean, and that same uneasiness transfers to the audience.
It’s psychological horror with very few jump scares, focusing more on a slow, creeping dread as Simon’s will to live teeters between survival instinct and madness. That, and the looming threat of something big and unknown just outside the sub.
Though not necessarily a gorefest, be aware that this film broke the record for the sheer volume of fake blood it used. The beginning is slow. But when the blood rains, it pours.
The movie deviates from the game quite a bit in the second half, leaning more heavily on cosmic horror than on just a big, alien fish. Some of the changes help to create a more tense atmosphere and additional scares at the cost of raising more questions without answers. Whether these new plot elements are meant to be up to interpretation or are just confusing is, well, up to interpretation.
While you don’t have to have played the game or be a fan of Markiplier to enjoy “Iron Lung,” it still helps to know some of the game’s lore since a few topics are mentioned in the movie, but not elaborated upon.
“Iron Lung” is a blood-soaked, claustrophobic sci-fi horror film with a slow beginning that really helps to create a feeling of sinking dread in the audience. It’s a passion project born from a YouTuber’s love of an indie-horror game, and translates the source material to screen with only some clunky plot additions. “Iron Lung” might not take your breath away, but don’t be surprised if halfway through it you have to remind yourself you’re not running out of oxygen.
