As with any adaptation, The New Mutants takes some creative liberties with its source material. In the translation from comic book to film, one of the biggest changes is to Limbo.
In the 1983 miniseries Magik: Storm & Illyana, by Chris Claremont, John Buscema, Sal Buscema and Ron Franz, Limbo is properly introduced into Illyana's backstory. In this story, it's established that the demon Belasco, who rules over Limbo, kidnapped Illyana as part of his plan to bring the Elder Gods to rule Earth. Belasco turned a portion of Illyana's soul demonic, creating several bloodstones and placing them within the Beatrice Medallion. By creating five bloodstones, Belasco intended to have Illyana become the Darkchilde and thus allow the Elder Gods to invade Earth.
While in Limbo, Illyana rebelled against Belasco and her newly found demonic nature, learning sorcery from the alternate universe version of Storm who resided there. She also trained for physical combat under the tutelage of Cat, an alternate universe Kitty Pryde. In Limbo, the passage of time is vastly different from the real world, allowing Illyana to age nine years and experience years' worth of training in the span of mere seconds in the real world.
After the deaths of Storm and Cat, Illyana ran away from Belasco. Once she returned, she had conjured the soulsword, described as "the ultimate expression of her mystical power." She wielded this weapon in a fight with Belasco, forcing him to revert to his human form and surrender. Instead of killing him, she let him live out of mercy, though she drove him out of Limbo.
In New Mutants #14, after defeating Belasco, his servant S'ym pledges his allegiance to her. Having won yet another battle, Illyana Rasputina became the undisputed ruler of Limbo.
The comics present Limbo as hell for Illyana, a prison she's forced to endure as years of her life are stolen from her. In The New Mutants film, Limbo is presented as the exact opposite: her happy place. Limbo in the film is not the source of Illyana's trauma, but rather the place she goes to escape it. The dimension makes its first appearance in the film nearly an hour into its runtime when Illyana accuses Danielle Moonstar of manifesting the horrors in the hospital. Magik lunges at Dani, opening a portal to Limbo until Dani makes her see a vision of the demons who assaulted her as a child. Cecilia Reyes then injects Illyana with some sort of tranquilizer to subdue her.
As a result of this altercation, Dani pays Illyana a visit in her rooms afterward. She asks where Illyana "took" her to while they were fighting, referring to it as a "hell." Magik replies, "Limbo. A place we made up...me and Lockheed." Illyana continues, "at first it was just our special place, we went there in our minds whenever something bad was about to happen. We went there so much...stayed there so long...it became real."
In this story, not only is Limbo somewhere Illyana goes to of her own free will, but by the story's own admission, she went there so much she helped it become real. Limbo in The New Mutants is a physical manifestation of Illyana's safe space in her own mind, rather than a hellish dimension she was held captive in.
She returns to this safe space later on when the demons from her memories attack the hospital. Unable to fight and having a panic attack of sorts, Magik retreats to Limbo via one of her stepping discs, leaving Sam Guthrie to handle the demon horde by himself. Afterward, she pops out of her disc, wields her soulsword and is able to fight the demons herself, having cleared her head in her happy place.
The film's director, Josh Boone, told explained that the choice to remove Belasco and instead interpret Limbo as a psychological entity for Illyana was important for keeping the tone of his story. Insisting that he didn't change much about the hellish dimension, he said, "You're not going to see, like, the demon Belasco. All the mythology from the comic book has been honored, but not the stuff that's really difficult to explain without a lot of crazy X-Men backstory… So I'd say everything about Limbo is the same, except it's now tied so psychologically into her backstory and has less to do with the demon named Belasco that nobody's going to really connect with or understand, and is going to clash so much with the tone of the movie."
It's unclear without Belasco and Storm just how Illyana was able to learn magic, but it's assumed she either learned it in Limbo or that sorcery is simply a part of her mutation in this universe. The New Mutants version of Limbo is the exact opposite of its comic book counterpart, a safe place that Illyana wants to retreat to instead of a hellish prison that took away years of her childhood. It's also assumed that Illyana is likely the ruler of Limbo simply because she created it in the film, rather than her fighting off S'ym and Belasco and taking the title for herself like in the comics.
Directed and co-written by Josh Boone, The New Mutants stars Maisie Williams as Rahne Sinclair/Wolfsbane, Anya Taylor-Joy as Illyana Rasputin/Magik, Charlie Heaton as Sam Guthrie/Cannonball, Henry Zaga as Roberto da Costa/Sunspot, Blu Hunt as Danielle Moonstar/Mirage and Alice Braga as Dr. Cecilia Reyes. The film is now in theaters.