Yellowstone Star's New R-Rated Horror Movie Is Officially Making History

EXCLUSIVE: One of the stars of the Yellowstone franchise is in the upcoming horror film Beware Boiúna, and the director is revealing how the story breaks new ground for the genre.

Beware Boiúna centers on a group of doctors who travel into the Amazon rainforest for a humanitarian medical mission. When a Brazilian mythological serpent known as the Boiúna is awakened, everyone is suddenly in danger and forced into survival mode. Marshals' Logan Marshall-Green stars in the film with Kiana Madeira, Jessica Rothe, Jackson Bews, Juan Pablo Shuk and Vicente Peña.

In an interview with ScreenRant's Liam Crowley, director Mike P. Nelson explained that he decided to remove the shapeshifting element from Boiúna and instead ground the film in reality because he wanted to "blend mythology and science together."

As he acknowledged, a lot of storytelling is already rooted in reality, like the Titanoboa from the Paleocene era, so this film allows Nelson to explore what would happen if these creatures existed while "people were still living in the Amazon."

With this movie, the filmmaker is able to bring together "that mythos and question and wonder and keep that mystery there: is there something spiritual about [Boiúna], or is she just a creature?" Nelson believes it can be looked at both ways.

ScreenRant: "This film introduced me to Brazilian mythology. And what I found in my research about Boiuna is that this creature can also shapeshift. What went into your decision of omitting the shapeshifting element, and instead grounding it in reality?"

Mike P. Nelson: "I wanted to blend mythology and science together. So I think a lot of storytelling comes from things that are in reality already. So I feel like with a creature like the Titanoboa, which was from the Paleocene era, 50 million years ago, if something like that still continued to exist, look, 90 percent of the Amazon hasn't been explored yet. If something like that were to have existed while people were still living in the Amazon, is that something where stories were rooted? And so for me, I love the fact that we could bring in that mythos and question and wonder and keep that mystery there: is there something spiritual about her, or is she just a creature? I think you can look at it both ways, to be honest with you. And to me, it was all about the mystery remaining there."

If a sequel to Beware Boiúna ever gets made, the possibilities are wide open to explore other mythological creatures, like the Boitata, a giant snake with horns that breathes fire. Nelson conducted plenty of research and found the photos to be "insane," indicating that he's excited about what might come next if given the chance.

ScreenRant: "I dig it. I hope we get Boitata on the sequel. You know what I'm talking about? There's another snake with bullhorns, and it breathes fire, and I feel like it's like a sister monster to Boiuna."

Mike P. Nelson: "Oh yes. That's right, when I was doing the research, the pictures online are insane."

Before a sequel can even move forward, Beware Boiúna needs to be released first, and that will happen on October 2, two weeks after it screened at Fantastic Fest.

The film marks Nelson's fourth feature-length project, after The Domestics, Wrong Turn and Silent Night, Deadly Night. He also directed the Friday the 13th short film Sweet Revenge along with several other shorts.

Before joining the cast of Beware Boiúna, star Marshall-Green had appeared in movies like Prometheus, The Invitation, Snowden, Spider-Man: Homecoming, Upgrade and Carry-On. His small-screen credits include The O.C., When They See Us, Big Sky and And Just Like That...

This year, the actor starred in two major projects: Christopher Nolan's The Odyssey (which has grossed $1.7 billion) and Marshals. The latter is a spinoff of Taylor Sheridan's hit Yellowstone and the fourth series to debut in the franchise. Marshall-Green plays former Navy SEAL Cal Calvin, who joins the U.S. Marshals to get a new start in life.

Marshals season 2 premieres October 4 on CBS, which is just two days after Beware Boiúna is released, which means Marshall-Green will get plenty of screen time yet again come October.

Beware Boiúna will be released in theaters on Friday, October 2, 2026.

Cast

• 

  Logan Marshall-Green

  Brennan Malloy

• 

  Kiana Madeira

  Uncredited

• 

  Jackson Bews

  Shawn

• Juan Pablo Shuk

  Miguel

A medical mission in the Amazon becomes a struggle for survival against the Boiúna, an ancient predator protective of its domain.