During his decades-long career, Mexican filmmaker and author Guillermo del Toro has worked on a number of projects that never progressed beyond the pre-production stage. Some of these projects fell into development hell and are presumably canceled, while some were taken over and completed by other filmmakers.

1990s Omnivore Del Toro spent three years preparing to direct his first feature—a claymation sci-fi film titled Omnivore—in the early 1990s. The premise focused on the plight of a lizard-man born in a savage land where everything tries to eat everything else. Del Toro was inspired by Mexican stop-motion sculptor Marcel Delgado to create a different kind of monster film, and had written the story entirely in the Uto-Aztecan language Nahuatl. "It was a very late teens, early twenties, underground comix-type of story," del Toro said of the project in 2023. "Very pop, heavy metal." With the help of his brother and then-girlfriend, 120 puppets were fabricated in clay, and sets were built, but were left unattended and then vandalized. "They had destroyed every puppet, they had pooped and peed on the floor. And I turned around and I said, 'I'm gonna do Cronos. I'm gonna do a live action movie'." The only surviving materials from Omnivore were del Toro's storyboards, which were lost over time following several moves.

Meat Market: A Love Story Meat Market, an original screenplay by del Toro co-written with Ron Perlman, was described as "Hamlet in a meat market, by the way of Phantom of the Opera". Del Toro wanted Perlman to star in the lead role, but lost interest in pursuing the project when he believed he had become too old to play the part.

Silver Following Cronos, in the early 1990s, del Toro began writing a film called Silver, about a Mexican luchador wrestler who discovers that all politicians are vampires. In 2006, he stated that he had been wanting to shoot a new film in Mexico again but that he was "stuck on page 60" of the screenplay for Silver. In 2014, del Toro voiced his intentions to film a "small" low-budget film in black-and-white before beginning production on Pacific Rim 2, which he was attached to direct at the time. He spoke of casting John Hurt in an undisclosed role, as well as a lesser-known actress for the female lead. In 2015, this project was revealed to be Silver, which he was then said to be making following Crimson Peak instead of The Shape of Water.

Mephisto's Bridge Del Toro wrote an adaptation of Christopher Fowler's novel Spanky entitled Mephisto's Bridge, about a billboard designer who sells his soul to the devil. The first draft of the script was completed in 1994 and the film nearly went into production in the mid-2000s, but it did not go beyond pre-production. In 2001, del Toro called the screenplay a metaphor for his experiences in Hollywood. In 2008, he revealed that Fowler had awarded the rights to another production company, so the project was officially dead.

At the Mountains of Madness As early as 1993, del Toro had begun sketching images for a film adaptation of H. P. Lovecraft's At the Mountains of Madness; completing a first draft of a screenplay five years later. The project was deemed too daunting at the time as digital effects were not complex enough to render the shape-shifting creatures radically enough. By 2003, he was said to be working on co-writing the adaptation with Matthew Robbins. It was originally in development at DreamWorks Pictures under producers Susan Montford and Don Murphy, but would be cancelled. In 2006, del Toro took it to Warner Bros. but had trouble getting financing. At this stage, William Stout had completed preliminary art designs and Ron Perlman was rumored to play the role of Larson. In 2007, the project was acquired by Universal Pictures when del Toro signed a first-look deal there and when Hellboy II: The Golden Army was green lit. Plans were then put on hold when del Toro accepted the offer to co-write and direct two installments of J. R. R. Tolkien's The Hobbit, which he ultimately dropped out of. In July 2010, it was officially announced that he would direct At the Mountains of Madness as a 3D film for Universal, with James Cameron producing. Del Toro confirmed that he wanted Tom Cruise for the lead, and that the film would begin production as early as May 2011 and start filming in June. Earlier that same year, del Toro had also asked S. T. Joshi if he wanted to be a consultant once the film got into production. However, in March 2011, it was announced that Universal refused to greenlight the project over concerns of the $150 million budget and del Toro's insistence that it be released with an R rating rather than PG-13. In 2013, del Toro stated in an interview that he would try one more time to get the picture made, with Cruise still attached. In 2014, del Toro expressed leniency toward a PG-13 rating, saying that there was a possibility that the film would be made through Legendary Pictures (who produced his film Pacific Rim). Ever since its cancellation, del Toro has promised he would release all of the extensive pre-production artwork which was prepared for the film and never used. "We did over 300 pieces of art," he said in 2017. "We did storyboards, we did models... we had a whole presentation. You will cry, you will go, 'Why?' " In December 2021, del Toro revealed that At the Mountains of Madness was pitched to Netflix, after signing a multi-year deal with the streaming service in 2020. The filmmaker stated: "Take a wild guess which were the first projects I presented, you know? I went through the cupboard and found Montecristo and Mountains of Madness. Those were a couple of the ones I presented first." Del Toro further iterated that he intended to rewrite the script and make it a smaller, weirder and more esoteric version in respect to the scenes that he had left out before. Del Toro cast doubt if Tom Cruise would star in the project in the foreseeable future due to his age. In 2025, del Toro affirmed that the film was still on his bucket list, but that "it's too big, too crazy, too R-rated" and not what he wanted to make right then.Guillermo Del Toro Will 'Do Something Very Different' After Frankenstein: 'This Movie Closes The Cycle'

The Left Hand of Darkness In 1994, del Toro began writing an adaptation of Alexandre Dumas's The Count of Monte Cristo with L. M. Kit Carson and Matthew Robbins, titled Montecristo, later renamed The Left Hand of Darkness. His version was set in Mexico and was called a "steampunk gothic western". According to del Toro, he met with Nicolas Cage to play the lead role. The screenplay was rewritten by del Toro at around the time his father was kidnapped and held for ransom, and he has since described it as having "a lot of rage." In 2000, the project was presumably moving forward with American Zoetrope producing, but it was put aside in favor of The Devil's Backbone and Blade II. In 2002, del Toro provided further details on the film: "It's a very gothic adaptation of the book. I've always thought that Dumas wanted to evoke the spirit of the One Thousand and One Nights, his fascination for the Orient. Each adaptation was an adventure film or a classic movie without any invention, exoticism. So I wondered what would give this book adapted as a western [...] In the book, the Count is often mentioned as a 'pirate', a 'vampire', a 'thief'. He's very dark. And in my adaptation, the Count only goes out at nights. He's very close to a Dracula coming from a western, all dressed in black, red and gold. He has a mechanical arm that allows him to draw his gun faster than every one. [...] Monte Cristo will be a very catholic movie. [...] I've been trying to make this project for 10 years now. I always have these images with me. But the movie is so huge in my mind that I must find the perfect conditions to make it." He also described the film as being technically challenging in a 2008 interview with Den of Geek: "I think that's a movie that still bugs me a little bit. I mean, when you ask me if I'm scared of The Hobbit, I'm not, I'm more scared of Left Hand of Darkness, because it's a movie that I'm very, very proud of the screenplay, but it requires a set of tools that are a little daunting. It's sort of like a David Lean, Sergio Leone epic western. Very much full of magic. And it's the only movie without any creatures."

In 2013, del Toro said that it was one of the projects he would still love to do and that Legendary Pictures was very close to financing it, but were torn between making Crimson Peak instead, which was ultimately chosen in its favor. However, a 2026 IndieWire article indicated del Toro "has several projects on the burner" including "a rewrite of The Count of Monte Cristo as a gothic Western."

The List of Seven Del Toro was attached to direct an adaptation of Mark Frost's 1993 novel The List of Seven. Frost himself wrote a draft of a screenplay before the project was cancelled. In 2003, del Toro joked that it had become a "tradition" to talk to Frost each year to plan another way of gathering financing for the project. "When we wrote it, Steampunk had not yet taken hold. Many movies have done stuff like it now, with varying degrees of success," del Toro explained. "But List of Seven remains as powerful today as it was when we adapted the novel."

Light Years The impetus for del Toro's film Mimic originally began in the form of an unmade anthology film titled Light Years, which was to feature four short science fiction segments, "but with a different bent for each." The other directors were Bryan Singer, Danny Boyle and Gary Fleder. According to del Toro, the studio opted to abandon the project and morph his and Fleder's segments into features instead. "I initially said I don't think there is enough there for a feature," del Toro recalled. "I think it is a perfect short, but there's not enough there for two hours." Boyle was the only one able to film his segment, though it has never been shown, whereas Fleder's was later made as Imposter in 2001. Del Toro described Singer's as "very abstract, very philosophical".

The Sandkings Around 1995, before directing Mimic, del Toro approached George R. R. Martin with the intent to make a film adaptation of his famous novelette Sandkings, but the project was quickly scrapped after the novel was adapted into the first episode of the television series The Outer Limits.

Superstitious In 1997, it was reported that del Toro signed a deal to direct an adaptation of R. L. Stine's horror novel Superstitious for Dimension Films. He wrote a script, but the project remains unproduced.

Exorcist: Chapter 4 Verse I In the late 1990s, between the releases of Mimic and The Devil's Backbone, del Toro pitched himself to direct a fourth installment in The Exorcist film series for Morgan Creek Entertainment. His version would have been titled Exorcist: Chapter 4 Verse I and would have seen Father Merrin brought in to investigate the murder of a priest by a possessed child in the Vatican during World War II. Del Toro later spoke of the project in a live interview in 2006: "[The story] was very epic, setting up what followed. So I finished my take about The Exorcist and [the Morgan Creek executives] listened patiently and then said, 'That's fantastic, but there's only one thing. We want the movie but we don't want there to be an exorcism in it.' So I said, 'But it's called The Exorcist.' 'Yeah, but the last movie had an exorcism and it didn't make money.' That was the last meeting I took on that one. But that's sort of the Hollywood principle." Instead, the prequels Exorcist: The Beginning and Dominion: Prequel to the Exorcist were made by directors Renny Harlin and Paul Schrader respectively, but were both critical and financial failures.

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