Marvel did the unimaginable when it started cross-pollinating its movies. As the tapestry of the Marvel Cinematic Universe kept growing and growing, fans got to know all sorts of characters that never would have made it to the big screen were it not for the studio's unprecedented success. Characters like the Guardians of the Galaxy, Doctor Strange and Ant-Man became household names, and their popularity could rival any of the biggest names on the Avengers roster. After 10 years of cohesive storytelling, Marvel had its biggest year yet with Black Panther, Avengers: Infinity War and Ant-Man and the Wasp, a sequence of movies that brought the studio's total number of films to a whopping 20. Each new movie informs the other, and contributes to the overarching narrative at play. But while things appear definitive in the movies, certain things almost never happened.

Crafting an entire universe of movies is a complicated affair. With an increasing number of fan-favorite characters, there comes a time when Marvel's creative teams are facing an embarrassment of riches. Which character will crossover next, and which unlikely duo will team-up next? What movie will the next after-credits scene set-up? When we watch the films, Marvel's plan seems clear, but the truth is, sometimes it was more in flux than we'd imagine. Certain scenes were crafted to be different than what we saw, and certain characters could have appeared in surprise places. Today, CBR revisits 10 years of the MCU and the 20 films Marvel has given us to list 20 behind-the-scenes last minute changes that could have actually changed everything -- some of them even better than what we got.

20 ANT-MAN: TEAM STARK?

Captain America: Civil War was a big deal because it was set to pit Avenger against Avenger, friend against friend. But on top of that, the movie was set to feature more Marvel superheroes than any other movie before it. While fans were delighted to see Spider-Man join the fray, there was a time when that wasn't the case.

With no Spider-Man, the producers of Civil War looked at other characters who could have filled his shoes, and Ant-Man was at one point set to play the role of Spider-Man on Team Stark. That certainly would have been interesting to see, especially considering the animosity that there is between Hank Pym and the Stark family.

19 CAPTAIN MARVEL IN AGE OF ULTRON

At the end of Avengers: Age of Ultron, Captain America and Black Widow walked into their new facility to greet the next recruits for Earth's Mightiest Heroes: Falcon, War Machine, Scarlet Witch and the Vision -- all of them characters that we had seen earlier in the film in some capacity.

However, there was a time when the ending of the movie was supposed to introduce Carol Danvers' Captain Marvel in the closing moments of the film, in order to surprise fans and generate even more excitement for the future. That certainly would have been quite the surprise, but the powers that be decided that some people might just be wondering who this newest recruit was.

18 WASP COULD HAVE DEBUTED IN CIVIL WAR

The mid-credits scene of Ant-Man teased the full debut of Hope Pym's Wasp. However, fans would have to wait three years for the female superhero to finally spread her wings in Ant-Man and the Wasp. However, this wasn't always the case. At a certain point, the character was originally set to debut much sooner than that – in Marvel's next film following Ant-Man, Captain America: Civil War.

When the producers of Civil War were choosing which superheroes would appear in the film, it was part of their original plan to introduce the Wasp. However, since the film was already filled with so many characters and storylines, it was ultimately decided to hold off on the Wasp's proper introduction.

17 THE HULK MID-CREDITS TAG THAT NEVER HAPPENED

Following the events of Age of Ultron, the Hulk would then leave the Earth aboard the Avengers' quinjet and somehow land on the planet Sakaar, where he would become a fan-favorite champion. At the time, one of the mid-credits scene of the second Avengers film was actually supposed to feature the Hulk, in the quinjet, heading off into space.

However, the scene never made it into the final cut of the film. Why? Because of leaks. Before the movie was released, a leak led to certain websites running with the rumor that Age of Ultron would set up a “Planet Hulk” storyline. But Marvel didn't want these websites to be right, so the plan got scrapped.

16 ANT-MAN, FOUNDING AVENGER

Back when the Marvel Cinematic Universe was still in its infancy, there were three movies on Marvel's docket: Iron Man, The Incredible Hulk, and Ant-Man, which at the time was supposed to be directed by Edgar Wright. If that plan would have worked out, then Ant-Man would have been on the original team of Avengers.

However, that didn't turn out to be the case. Wright's Ant-Man ended up getting delayed, while Marvel's plans went full steam ahead. Instead, Ant-Man finally appeared on the screen after the second Avengers movie, Age of Ultron. But at least he did become an Avenger in Civil War. Well, sort of.

15 A HAWKEYE CAMEO IN WINTER SOLDIER

After the events of 2012's The Avengers, Captain America joined S.H.I.E.L.D. alongside Black Widow. Together, the two went on missions, as we saw in The Winter Soldier, a movie that featured the spy agency in an important capacity. Nick Fury was there, as was Mariah Hill. But where was Hawkeye?

While the archer didn't appear in the film, there was a time when he was supposed to. Clint Barton was supposed to be dispatched by Alexander Pierce to go after Steve Rogers after he had gone on the run. Then, Clint would have found Cap and the two would have faked a fight while Clint told his fellow Avenger that he was being tracked by S.H.I.E.L.D. through his suit.

14 AN AWESOME ENDING FOR THE DARK WORLD

Thor: The Dark World ranks perhaps as fans' least favorite Marvel movie. However, perhaps these people would have changed their minds had the movie featured its original ending: while battling a Reality Stone-powered Malekith during the convergence of all Nine Realms, Thor was supposed to summon lightning from all nine worlds to destroy the villain.

Such an impressive feat would have been one of the most spectacular scenes in all of the MCU films. However, that plan was put to the side because it was decided that Thor should instead receive a bit of help from his human allies Jane Foster, Erik Selvig and Darcy.

13 ULTRON IN THE FIRST AVENGERS MOVIE?

The artificial intelligence known as Ultron was the main antagonist of the second Avengers film. The villain was created in the opening segments of the film and, ultimately, destroyed by its end. However, Ultron was originally supposed to appear much sooner than that. In fact, the villain was supposed to be teased in 2012's The Avengers.

Thanks to a deleted scene from the first Avengers film that was pre-visualized but never actually shot, we saw that, before facing Loki in Stark Tower, Iron Man was supposed to witness the first step in J.A.R.V.I.S.' evolution into what would become Ultron. However, the scene was cut to keep the focus on Loki... and Thanos.

12 AVENGERS TOWER COULD HAVE BEEN IN AMAZING SPIDER-MAN

After the massive success of 2012's The Avengers, another Marvel movie would release that same summer: The Amazing Spider-Man, starring Andrew Garfield as the titular superhero. At the time, there was no Tom Holland, no Captain America: Civil War and no deal between Marvel and Sony to share the character.

But still, the Spider-Man film was almost a part of the MCU. In fact, it was revealed that the Avengers Tower was almost digitally added to be a part of the New York skyline in the movie. However, due to a lack of time, the building was never added into the film.

11 THE DEFENDERS WERE CONSIDERED FOR INFINITY WAR

Almost as soon as Daredevil launched on Netflix, some fans began wondering if the Man Without Fear would ever appear in the big screen movies of the MCU. The questioning only grew louder with the arrival of Jessica Jones, Luke Cage and Iron Fist, with every fan clamoring for a team-up between the two superhero teams.

By all accounts, it seemed like Infinity War would have been the best time to get all the superheroes of the MCU involved. Well, as it turns out, the Russo brothers did consider the Defenders for Infinity War – very briefly. As it turns out, the logistics of a television shoot versus that of a movie made an appearance impossible. But it was, at least, considered.

10 WHY WASN'T LOKI IN AGE OF ULTRON?

When the trailers of Avengers: Age of Ultron were released, most fans were excited to notice that Tom Hiddleston's name was featured in the cast of the film. Even certain interviews with the cast and crew of the film confirmed that Hiddleston had shot a scene for the movie -- and yet we never got to see it.

The scene ended up being cut, with no real explanation as to why. It's even unclear where such a scene would have fit in. A strong theory states that Loki could have appeared during Thor's visions, but we simply don't know. Perhaps this would have been how Thor discovers that his brother was still alive, and posing as his father?

9 HULK'S NEMESIS COULD HAVE RETURNED

Outside of a few line of dialogues and the return of General Ross, most movies of the Marvel Cinematic Universe don't actually reference The Incredible Hulk all that much, mainly because it starred Ed Norton instead of Mark Ruffalo. However, the movie's villain could have made a surprise appearance.

That's right, Tim Roth's the Abomination was at a certain point considered to return in Avengers: Age of Ultron, according to the actor himself. However, that never happened. It would certainly have been nice to see the villain return, even if we don't know how he would have fit in. Our best guess? Hulk would have seen Abomination due to Scarlet Witch's hex, when in fact he would have been fighting the Hulkbuster.

8 GRANDMASTER'S VISIT TO EARTH

Thor: Ragnarok ended with Asgard decimated, and Thor now leading what little of his people were left back to Earth. However, there came very close to being a surprise character in his flock. In fact, Jeff Goldblum's Grandmaster was supposed to be among the refugees, very much looking forward to visiting Earth.

Director Taika Waititi confirmed that such a scene in fact existed, but that it wasn't ultimately used. Instead, we only saw the Grandmaster face the people of his planet after an uprising. But it's interesting to wonder what sort of trouble he would have gotten himself into on Earth.

7 A DIFFERENT MENTOR FOR PETER PARKER

Spider-Man: Homecoming teamed Peter Parker up with Tony Stark as his mentor. Throughout the film, Tony guided the young superhero, trying to turn him into a better superhero than he could ever hope to be. However, Iron Man wasn't always supposed to be Peter's mentor. Originally, Spider-Man would have had a very different mentor: Nick Fury.

That's right, for a time, it was considered that Samuel L. Jackson's Nick Fury was going to be the co-lead of Homecoming. We imagine that Fury, who now found himself without a S.H.I.E.L.D. role, would have tried to continue to find and train young superheroes, much like he did in the comics with his Secret Warriors.

6 FALCON AND IRON MAN: SPACE BUDDIES

In Avengers: Infinity War, the Avengers got split into several groups in their fight to stop Thanos. Most were on Earth, but Iron Man and Spider-Man went after Ebony Maw, in space, in order to save Doctor Strange. There, the mentorship between Tony and Peter continued to evolve and grow. However, Tony was originally supposed to have a very different wingman: Sam Wilson.

The Falcon is a superhero more closely associated with Captain America, which means that it would have been quite interesting to see these two trapped in space together. That pairing would have been much different, but it was changed to Spider-Man in order to have a more emotional impact at the time of Thanos' snap.

5 A DIFFERENT VILLAIN IN IRON MAN 3

Iron Man 3 gave fans a bit of a controversial twist when it revealed that who everyone thought the villain of the film was supposed to be, the Mandarin, was in fact nothing more than an actor hired by Alrdich Killian. As it turns out, Killian was the real villain of the film, the one pulling all the strings against Tony Stark.

However, that wasn't always the case. During the production of the film, there was a time when Maya Hansen, who plays a bit of a reluctant villain in the film before getting killed by Killian, was supposed to be the main antagonist of Iron Man 3, preceding Ant-Man and the Wasp's first female MCU villain by five years.

4 MARVEL'S FIRST VILLAIN WAS SUPPOSED TO SURVIVE

Obadiah Stane's Iron Monger was the first villain of the Marvel Cinematic Universe. Over the course of Iron Man, we learned that he was the one behind Tony Stark's kidnapping in the Middle-East, and he used the technology of Stark's arc reactor to power his own nefarious suit. The two fought, and Stane was defeated thanks to a bit of help from Pepper Potts.

The detonation of the factory's arc reactor led to Iron Monger's death, but it turns out that Stane wasn't always supposed to die. Actor Jeff Bridges stated that Stane was originally meant to survive the first Iron Man film, which could have led to further appearances further down the line.

3 BUCKY WAS SUPPOSED TO GET HIS NEW ARM SOONER

Bucky Barnes lost his metal arm during the fateful battle between Iron Man, Captain America and the Winter Soldier in 2016's Captain America: Civil War. It would take two years for the character to get a new vibranium arm courtesy of the king of Wakanda, the Black Panther. However, Bucky was originally supposed to get his new arm sooner than that.

At first, it was considered that Bucky would get his new arm in the after-credits scene of the Black Panther film, where the former Winter Soldier is shown to live peacefully in Wakanda. However, it was decided that this scene should instead focus on Bucky's emotional state of being.

2 BANNER COULD HAVE APPEARED IN CIVIL WAR

Back when Captain America: Civil War was shooting, the rumor mill began churning like crazy when some people believed that Hulk actor Mark Ruffalo had been spotted on set. While the rumor turned out to be false, it didn't stop Marvel from confirming that Banner was considered to appear in the film.

We don't know in what capacity the actor would have appeared, but it was said that Banner was briefly considered to appear near the end of the film. Would he have hulked-out, or simply been present as a friend for Tony Stark? We simply don't know. Instead, we would find out that the Hulk was off-planet.

1 THE INFINITY SNAP WAS SUPPOSED TO BE IN AVENGERS 4

Avengers: Infinity War ended with the mother of all cliffhangers: Thanos, after collecting all Six Infinity Stones, brings his fingers together and snaps. As a result, half of all life in the universe is wiped out, including some of our favorite Avengers like Black Panther, Spider-Man, Doctor Strange and Star-Lord.

However, that wasn't always the plan. Originally, the fateful infinity snap was supposed to happen in Avengers 4, which would have considerably altered the ending of Infinity War and the mysterious story of its upcoming sequel. We can only wonder what the cliffhanger would have been, were it not for the snap.