WARNING: The following article contains spoilers for Deadpool 2, in theaters now.

Deadpool 2 is demanding, requiring its viewers not only to keep up with the fast pace of its story and action sequences, but to catch a barrage of jokes, sly references and Easter eggs. This is a film that surely will become only more rewarding with repeated viewings. A lot of those nods have already been found, with cameos and teases dropped in just for fun. But there are still a few that make us wonder whether the film is building toward something, beyond an X-Force spinoff, of course.

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The sequel makes a subtle reference to a major X-Men villain, who was previously teased in the Fox franchise. This time, it's a little more difficult to catch, but the nod is still there, and it once again comes in the form of a name: Essex. As in Nathaniel Essex, aka Mister Sinister.

Early in the film, Deadpool joins Colossus and Negasonic Teenage Warhead as an X-Men trainee on a mission to stop a teenager, young Russell (aka Firefist, played by Julian Dennison), who's attacking people in the streets. But Russell isn't lashing out for no reason; he's actually trying to escape his "school," the Essex Home for Mutant Rehabilitation. It's actually where mutant-fearing men conduct intensive experiments to try and suppress the powers of the children in their care.

In the comic books, Nathaniel Essex has always been one for genetic experiments and mutant/human DNA analysis, which makes it easy to believe that he might be behind this cruel school. To him, this could simply be another experiment to learn more about the response to mutant-suppression treatments.

What's more, Sinister doesn't get his name from anywhere. He's always been one to work more in the shadows and behind the scenes, which certainly lends credence to the idea that he's behind this establishment. After all, in the post-credits scene of 2016's X-Men: Apocalypse, three men who work for Essex Corp. walk into the Weapon X facility and collect the blood of Wolverine. It would later be used to create clone's of the clawed mutant, X-23 and X-24, who were both seen in Hugh Jackman's Wolverine swan song, Logan.

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This means the last three X-Men universe movies have featured Mister Sinister's influence in one form or another. Now, there was a time when some believed Sinister would be the villain of Deadpool 2 -- some even went so far as to theorize the character could be seen in the film's Bob Ross-inspired teaser -- but it has become increasingly clear Fox is playing the long game with the character.

As we already know that an X-Force movie is coming, perhaps that's where it's all been leading: Mister Sinister has slowly been built into the next big foe of Fox's X-Men movie universe; all that remains is for him to finally step out of the shadows and reveal his hand.

Directed by David Leitch, Deadpool 2 stars Ryan Reynolds as Deadpool, Brianna Hildebrand as Negasonic Teenage Warhead, Leslie Uggams as Blind Al, Stefan Kapičić as the voice of Colossus, and Karan Soni as Dopinder, with newcomers Zazie Beetz as Domino, Josh Brolin as Cable and Julian Dennison as Russell. The film is playing in theaters everywhere.