In addition to its "Fantastic Four" reboot in 2015, "X-Men: Apocalypse" in 2016 and a sequel to "The Wolverine" in 2017, 20th Century Fox has announced that in 2018, it will release an "Unnamed Marvel Project." Now, there's nothing fans love more than riddles and speculation, so this is the perfect time to take a look at what the prospective film could be. While Marvel retains film rights to the bulk of its catalog, there is still a large swath of its library that Fox has access to, giving the studio with the "X-Men" film rights -- including Wolverine -- and the Fantastic Four a plethora of cosmic and and inter-dimensional movie possibilities.

Fox Sets "Fantastic Four," "Wolverine" Sequel Dates; Announces 'Mystery' Marvel Movie

One thing is certain when looking at the future of Marvel character based movies: With the continuing success of Fox's X-Men franchise, Marvel Studios' record-breaking "Avengers" film and Sony's promise of releasing a "Spider-Man" movie every year, the Marvel Universe should rule the multiplex for many years to come. And with so many sub- franchises for Fox to choose from, ranging from the obvious to the unexpected, CBR plays detective by looking at the clues -- ranging from successes and failures from past films to those that have been rumored throughout the years -- to figure out what direction the studio might pursue next. How will that domination continue in 2018? Read on to find out...

"X-Men/ FF" crossover

Marvel Comics has a rich tradition of teams and heroes putting aside their differences for the greater good, it's time for film audiences to experience what comic fans have been embracing and debating for years: the crossover. And if Hollywood has learned anything from the success of "The Avengers," it's that crossover films do big box office. Fox controls two major Marvel properties, and the temptation to smash them together in one big cosmic blowout must be tempting. Of course, Fox has to be careful with this one, as the cosmic sensibilities of the "Fantastic Four" could be difficult to mesh with the more grounded X Universe, but imagine a film with Wolverine going toe to toe with Ben Grimm, Johnny Storm in a dog fight with Storm, or the mind of Reed Richards going against the telepathic abilities of Charles Xavier. Or, imagine what kind of threat would be needed for the two diverse teams to team up. Galactus, perhaps? Or how about spinning the crossover out of the next X-Men flick and feature Apocalypse as the villain?

Of course, whoever the X-Men and the FF could take on, the winners would be the fans as seeing two of Jack Kirby and Stan Lee's greatest creations sharing time on a movie screen would be too cool for words. This team-up would be a great way for Fox to introduce cosmic elements into the X-Men as well as make their "Fantastic Four" franchise more "legit" by teaming the new versions of Ben, Sue, Johnny and Reed with Fox's first superhero film success story. By teaming up their two franchises, the studio would be in a great position to potentially own 2018.

"Cable and X-Force"

There have been persistent rumors that Fox is in active development on an "X-Force" film. In 2018, after Fox presents two more "X-Men" films in 2014 and 2016, plus a new "Wolverine" in 2017, Fox may just want another X-film to add to their ever expanding empire. Marvel has had some success in recent years with a variety of "X-Force" titles written by creators including Rick Remender, Craig Kyle & Chris Yost and Dennis Hopeless, who all penned stories Fox could utilize as the basis for a potential "X-Force" film. Alternatively, they could mine the archives and go the classic X-Force route as steered by Rob Liefeld -- Cable, Domino, Shatterstar, over-the-top action and designs. Cable is the thread that keeps all the eras of "X-Force" together, and quite frankly, Fox would need a whole film to tell Nathan Summers' complex back story. Time travel is going to be a huge part of in "X-Men: Days of Future Past," leaving plenty of room to introduce the time-hopping Cable into the X Universe. (May we suggest this as a post-credits scene?)

Done right, Cable is a character who connects generations of X-Men and he would make the "X-Men" film franchise substantially richer with his one-armed presence. Whether modern day fans want to believe it or not, there are a great deal of lapsed '90s comic book readers out there who would have their nostalgia bone tickled by a big screen version of Cable, plus, the inclusion of X-Force could allow Fox to find a place to showcase newly introduced mutants like "Days of Future Past's" Cannonball and Warpath, or bring new characters to the big screen, like Rictor, Boom Boom or the more contemporary X-23 and Dr. Nemesis. "X-Force" is an extremely marketable concept that puts a twist on the tone and style of the "X-Men" and could serve as a fitting companion to Fox's already popular "X-Men" franchise.

"Silver Surfer"

Assuming Fox's "Fantastic Four" strikes a chord with audiences, there's one obvious direction to push the team -- toward Galactus. But before Fox can reintroduce the devourer of worlds in a future "Fantastic Four" film, it would be nice to spend a little time with the Silver Surfer, the cosmically-powered being who serves as Galactus' herald. Imagine how much more poignant Norrin Radd's self sacrifice could be if fans get to know the Surfer prior to his boss threatening to destroy Earth. A "Silver Surfer" film could not only introduce a new hero to moviegoers, but double as a slower introduction to the mind-blowing concept that is Galactus -- this time in all his glory, not just as a purple cloud. With "Guardians of the Galaxy" headed to theaters courtesy of Marvel Studios, a "Surfer" film could allow Fox to build their own cosmic Marvel U including the Shi'ar, the Brood, or even the Starjammers, all concepts and characters that can make a future impact on the "X-Men" films.

Gambit

Whether Channing Tatum's interest in the role pans out, or Taylor Kitsch makes a return as the Ragin' Cajun, Gambit would be a great solo character for Fox to explore. A "Gambit" film could provide a place for Anna Paquin's Rogue to shine, especially since Singer himself has stated that the Southern belle of the X-Men has been cut from "Days of Future Past." Rogue and Gambit's romance is the stuff of legend, and seeing it fully realized on the big screen could be amazing. Gambit also has a rich history away from the X-Men, from his time with the Thieves' Guild to his days as a mercenary for hire. No one has really tried a superhero caper flick, and a genre mash-up could offer a fresh take on the superhero genre. With Singer apparently thinking about Gambit (and Nightcrawler!) returning for "X-Men: Apocalypse" in 2016, things could be getting pretty exciting very soon for fans of the X-Men's most rakish member, which could in turn lead to Gambit stealing the spot of Fox's mystery film.

"X-Men" Producer Wants Channing Tatum For "Gambit" Movie

"Old Man Logan"

Wolverine is slated to star in his third solo film in 2017, and appears to be the central protagonist of "X-Men: Days of Future Past." That's a heck of a lot of Logan in a not very long period of time, so if Fox were to present another Wolverine film in the 2018 mystery spot, it would have to be different, bigger and something that will really cause fans to raise an eye brow. "Old Man Logan" is just such a story. Set far in the future, it's is essentially the final Wolverine tale, which would make it a perfect swan song for Hugh Jackman, especially in light of the actor's recent comments about eventually handing the role over to a new face. Of course, Fox would have to get a little clever with the plot, as Hawkeye and the Hulk play pivotal parts in the dystopian story, but, there are many characters Sony does have access to that could sub into those roles nicely.

"Old Man Logan" is a perfectly paced, ultra-violent tribute to Wolverine, the story of a time when Logan desperately wants to find peace in a world that desperately wants him to be the killer he was created to be. All the narrative plot threads from the first "X-Men" could come to a head in "Old Man Logan," allowing fans a catharsis if it were indeed Jackman's final turn as the character. To date, no studio has presented a deep look into a comic book character's future, or a third act which truly end a character's story. The closest we've come yet was in "The Dark Knight Rises," but that ended with Bruce Wayne in a cafe, while "Old Man Logan" ends with a snikt!

"X-Men: The Dark Phoenix Saga"

How big can Fox get? Well, the 2018 mystery movie could be the one story X-Men fans have been teased with but never truly got: "The Dark Phoenix Saga." Yeah, "X-Men: Last Stand" featured an out-of-control Jean Grey, but we all know that wasn't the true "Dark Phoenix Saga," not really. The real "Dark Phoenix Saga" is cosmic, huge and unforgettable. "X-Men: Days of Future Past" is about to take the X Universe on a trip through time, an adventure which could open the door for Jean Grey's return. The seeds have been planted: The debut of the Hellfire Club in "X-Men: First Class," the potentiality of cosmic shenanigans in "The Fantastic Four" and the fact that not once in an "X-Men" film have fans seen Jean 'Phoenix up.' "DoFP" could see a return of Cyclops as well, undoing some of the perceived damage inflicted upon the franchise by the often maligned third "X-Men" film. The movies never really did the tragic saga of Jean Grey justice, and with Bryan Singer back on board, 2018 could be the time to fix that mistake.