The most impressive thing about Iron Lung, the claustrophobic then ultimately cosmic horror cheapie directed by, written, and starring YouTube personality Mark Fischbach (AKA Markiplier), is that it takes a while to fall apart. Fischbach’s self-funded film notably expands on its source material, David Szymanski’s well-liked indie horror video game of the same name, and adds a series of tortured narrative convolutions to its main character’s already harrowing underwater mission. As a performer, Fischbach’s frantic performance can sometimes be distractingly monotonous, but as a filmmaker, he has an impressive eye not only for compositional details, but also for how his images cut and flow together.
Trapped in an experimental submarine with no external visibility beyond black, white, and grey x-ray-style camera images, Fischbach’s desperate protagonist mostly struggles to navigate his deceptively confined space. His grip on reality gives way faster than the integrity of the ship’s hull though, so he eventually starts to look inward, which shifts Iron Lung‘s focus away from nerve-wracking B-movie peril and towards a more character-driven sort of psychological horror. Thankfully, by this point in the movie, Fischbach’s already paved the way for his adaptation’s inevitably chaotic, but potently upsetting finale.
For a while, Fischbach presents Iron Lung‘s single location like a nautical-horror-themed escape room as his character, the stressed-out prisoner Simon, explores the titular sub. An imposing narrator hints at a post-apocalyptic backstory involving a cataclysmic global event called The Quiet Rapture, which mysteriously leaves a sliver of humanity to fight for survival with precious few resources. Simon’s mission begins as a vaguely defined resource/data-collection mission, but soon becomes a solo fight for survival after he loses contact with Ava (Caroline Rose Kaplan), the impatient radio dispatcher who gives Simon his orders through a tinny speaker. Before then, Simon has to make do with limited resources and even less contextualizing information.
To his credit, Fischbach carefully threads the needle for Simon’s later collapse through a more introverted story about penance, and a pre-dive incident that not only led to his imprisonment, but also his spiritual and physical breakdown. That’s sometimes hard to appreciate as Iron Lung plays out, since Simon’s dialogue mostly consists of frantic questions and declarative protests (and sometimes both), like “How many times are you gonna use me before you let me go?” and, “Why is it so fucking hot down here?”
More convincing is Fischbach’s attention to fetishistic detail, like his extreme close-ups of blood-red condensation as it sizzles and beads before falling from a leaky overhead pipe or the blown-out audio quality on the sub’s radio speaker. Fischbach subtly develops his audience surrogate character on this foundation of tactile, analog-horror-friendly touchstones. You never have to wait too long for Fischbach to find new and compelling ways to reframe his character as a roaming plot device, who spends most of his time searching for the next hidden fixture or flickering light to futz with. It’s easy to imagine an even more intimately scaled B-movie where Fischbach just explores the main cabin, making important discoveries about his mission and how he can survive as he goes. But the time Fischbach devotes to letting Simon root around his ship effectively hooks viewers for what could have otherwise been a one-trick genre exercise. As it is, Iron Lung is distinguished by the same creative ambitions that ultimately make its ending seem like a watery solution after such an airtight setup.
This type of story has to have a big sweaty gear shift to be anything more than a cool concept in search of an idea, and with its trippy, body-horror-meets-Lovecraft conclusion, Fischbach swings for the fences in a way that feels both necessary and reckless. The film is an undeniable breakthrough for the filmmaker, even if he’s got both too much chutzpah and too little experience to stick such a tough landing. Iron Lung‘s not a flawless debut, but it has a bright future as a cult classic.
Director: Mark Fischbach
Writer: Mark Fischbach
Starring: Mark Fischbach, Caroline Rose Kaplan, Troy Baker, Elsie Lovelock, Elle LaMont, Seán McLoughlin, Isaac McKee
Release Date: January 30, 2026
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