Marking his feature film debut, Iron Lung by Mark Fischbach arrives with a surprising amount of weight behind it.
Known to millions online as Markiplier, the Korean American creator has spent years building a reputation for ambitious interactive projects on YouTube.
With over 40 million subscribers, he has already demonstrated his storytelling and acting abilities through YouTube projects like In Space with Markiplier and A Heist with Markiplier. Still, stepping into the world of feature-length filmmaking is an entirely different challenge.
Going into Iron Lung, I was curious, if not slightly sceptical, about how well a minimalist indie horror game could translate to the big screen. What I found instead was a surprisingly confident and atmospheric film that leans heavily into tension, creativity, and sheer dedication from its creators.
The film is based on the 2022 indie horror game Iron Lung by developer David Szymanski. In the original game, the player controls a nameless convict sent to explore a vast ocean of blood on a desolate moon inside a small, rusted submarine known as the “Iron Lung.”
The game’s premise is deceptively simple, relying on atmosphere, sound, and imagination rather than traditional horror spectacle. It’s a concept that became popular online in recent years, thanks in part to content creators like Markiplier, who shared their experiences playing it.
The film adaptation takes that same premise and pushes it to new extremes. Much of the movie takes place inside the titular submarine, recreated in meticulous detail as a live action set that perfectly captures the claustrophobic dread of the original game. The cramped metal walls, dim lighting, and oppressive atmosphere create a constant sense of unease, making the Iron Lung itself feel like a character rather than just a setting.
Mark Fischbach plays Simon, a reimagined version of the game’s unnamed convict, bringing far more personality and emotional depth to the role than I expected. Opposite him, Caroline Kaplan plays Ava, whose presence adds an important dynamic to what would otherwise be an extremely isolated narrative.
Because the cast is intentionally small, the performances carry a lot of weight, and both actors manage to keep the tension alive even during the film’s quieter moments.
One of the most impressive aspects of Iron Lung is its sound design. In a film where much of the action happens in darkness or in tight spaces, sound becomes one of the primary tools for building suspense. Metallic groans, distant echoes, and the eerie ambience of the blood ocean all combine to create a constant sense that something is terribly wrong just beyond the frame. It’s the kind of sound work that quietly holds the entire film together, and it deserves serious recognition.
Another standout element is the creature design. Concept artist Molly Brown (known online as Deadlymelodic) helped bring some of the film’s most disturbing visuals to life, and the results are genuinely unsettling in the best possible way. When the horror elements finally emerge more clearly in the second half of the film, the creatures feel terrifying alien, and truly memorable.
Narratively, the script itself is fairly minimal. For large portions of the runtime, the story focuses almost entirely on Simon and Ava inside the submarine. However, rather than feeling empty, the film uses environmental storytelling and subtle clues scattered throughout the set to build suspense. Every flicker of a monitor or cryptic message adds to the mystery of what exactly is lurking beneath the blood-red ocean.
By the time the third act arrives, the film fully commits to its horror elements, shifting from slow-burn tension to moments of intense spectacle and gore. Compared to the relatively restrained first two acts, the finale hits like a shockwave, there were genuinely moments where I found myself gripping the edge of my seat, covering my eyes, unsure of what horrifying image might appear next.
From a production standpoint, the film’s achievements are equally impressive. Made on a reported budget of around $3 million, Iron Lung managed to earn roughly four times that amount during its opening weekend. The production also set a rather unusual record: using approximately 80,000 gallons of fake blood (over 300,000 litres!) making it the largest amount of blood used in a horror film. It’s a statistic that perfectly captures the film’s dedication to practical spectacle.
That said, the film isn’t without its flaws. There are moments where the pacing slows a little too much, and certain parts of the script could have been tightened to maintain momentum. But considering this is an independent debut without traditional Hollywood backing, those issues are relatively minor and don’t take away from the overall experience.
It’s also worth noting that familiarity with the original game does enhance the experience. If you already understand the mechanics and narrative framework of Iron Lung, you’ll likely appreciate many of the film’s references and creative expansions. Without that context, some elements may feel slightly obscure.
Perhaps the most surprising part of the film is how quickly you forget you’re watching a project created by a YouTuber. For the first twenty minutes or so, it’s hard not to see Markiplier rather than Simon. But as the story unfolds, the performance becomes convincing enough that you eventually lose yourself in the narrative.
For a debut feature, that’s a incredible achievement, and a thrilling ride for horror enthusiasts willing to dive into its blood-soaked depths. Ultimately, Iron Lung is an ambitious and impressively executed independent horror film. It proves that passionate creators with a clear vision can produce something that rivals much larger productions. More importantly, it feels like a glimpse into the future of filmmaking, one where digital creators like Mark can successfully bridge the gap between online content and mainstream cinema.