Mark Ruffalo claimed in one interview that he received multiple different scripts throughout filming just in case he let something slip.note Recall that he actually came within a hair of saying in an interview prior to Thor: Ragnarok that half the universe would die in the next film, and followed it up by bootlegging part of the movie.
Tom Holland was actually only given his lines, after he'd spoiled previous films to the point of it becoming a meme. In scenes involving green screening, he didn't even know who he was talking to.
According to the directors, Tony's funeral was given the production codename "The Wedding". According to Tom Holland during an appearance on Jimmy Kimmel Live, he didn't realize it was Tony Stark's funeral until he noticed that Robert Downey Jr. wasn't on set.
The Secret Empire's infamous line of Captain America saying "Hail HYDRA" to reveal himself as a HYDRA Agent appears, but in the context of him pretending to be one.
Blink and you miss it, but when the climatic fight is happening, as Stark is fighting against Thanos, there's a moment when the titan grabs Iron Man, and looks like he is about to split him in half, like in the comic "Thanos Wins."
In the end credits, the original six Avengers are billed last after every other major character, but their names are displayed with much more prestige than any others, and include the written signatures of the actors as well, creating a 'best-for-last' effect. Downey Jr. himself, the man who was the origin of the entire MCU, is billed dead last.
Blooper: Despite shrinking down and being busy hotwiring his van, Scott can be seen as Giant-Man shoving a Leviathan through a portal in the background as Black Panther is bringing them the Infinity Gauntlet.
California Doubling: New Asgard is in Norway, specifically Tønsberg going by the sign; however, the filming location was the village of St Abbs in Scotland.
Content Leak: Days before the film's world premiere, a five-minute clip containing several scenes from the film (mostly from the second and third acts) was leaked all over social media. The Russo brothers issued a letter telling fans again not to spoil the film to others and used the hashtag #DontSpoilTheEndgame.
Deleted Role: Katherine Langford was announced to have been cast in an undisclosed role that was later confirmed to be an adult version of Morgan Stark. She filmed her scene during reshoots but it does not appear in the film. The scene would have been them meeting and saying goodbye in the Soul World. The Russos stated it felt too repetitive with the end of the last movie, and it likely didn't help that they needed to contrive a way to let the audience know this was an adult Morgan so they wouldn't be confused at Tony seeming to have a big emotional moment with some random woman.
Demand Overload: Ticket pre-sales for this movie causedmultiple ticket sites throughout the world to either crash or slow down. To give a perspective on this, the film was able to claim the highest box office pre-sales record in six hours.
Co-director Joe Russo claimed that Steve created another alternate timeline when he went back to the 1940s, and then traveled back to the original one after Peggy passed away. Since this take is consistent with the time travel logic explained in the film, most fans defer to this explanation.
Meanwhile, screenwriters Markus and McFeely say they believe that alternate timelines are only created when removing the Infinity Stones (which Steve didn't do on that trip), so it was a Stable Time Loop. In practical terms, this means that Steve was always Peggy's mysterious husband, and Steve did not intervene in history in spite of knowing what would happen (as far as we know) to preserve his timeline. They say that they had always intended this as far back as Winter Soldier.
Meanwhile, when asked about the two contradictory takes and which one was accurate, Kevin Feige simply responded to the AMA question with a one-worded answer: "Yes."
A lot of fans correctly guessed that the film's subtitle would be Endgame.
Many people guessed the first scene would be Clint's whereabouts when the Snap took place. They also correctly guessed that all of his family would be killed by the Snap, thus leading to him becoming Ronin.
Though it wasn't as widespread as the above, the news that Endgame would feature a five-year Time Skip was correctly guessed based on what little information that was given. Furthermore, the fact that it's permanent is another theory that became true.
Way back in "Thor's hammer" scene in Avengers: Age of Ultron, many people suspected Steve could actually lift Thor's hammer and was merely pretending not to.note Alternatively, it's been theorized that Steve was not yet fully worthy to wield it because he was hiding from Tony that Howard and Maria Stark were killed by the Winter Soldier. As we find out, they were right in the most awesome way possible. Said word-for-word by Thor when it happens.
When the Russos refused to confirm whether or not Jane Foster had survived the snap back in 2018, claiming that it might be a spoiler, some fans theorized that this meant Jane would have a cameo in Endgame. The theory picked up more steam when Natalie Portman unexpectedly showed up at the movie's premiere. In the actual movie, Jane does indeed make an appearance when Thor and Rocket time travel back to Asgard during the events of Thor: The Dark World, made up of both archive footage from that movie and some new dialogue that Portman recorded herself. The screenwriters said in an interview that Jane originally was slated to do more, but that role was given to Frigga instead since it was decidedly more emotional that way.
After an offhand comment in Ant-Man and the Wasp established the existence of time vortexes in the Quantum Realm, many fans guessed that they would be used to undo the snap somehow. While they didn't end up doing it directly as most theories assumed, they were instrumental in retrieving past versions of the Infinity Stones to handle the job.
Many felt that Bruce and Hulk's arc in Infinity War was building towards Professor Hulk.
Shortly after the release of Infinity War, Kevin Feige explicitly confirmed that the movie would not be called Avengers: The Infinity Gauntlet. The Russos would later indirectly confirm that Avengers: Secret Wars would not be the title of the movie either, as they said that they would be interested in adapting the original comic event a long time after Disney's acquisition of Fox.
Despite what some fans had hoped and theorized, Quicksilver is not resurrected during the movie.
When it came to speculation regarding the Time Skip, and the confirmation that Cassie Lang was recast to Emma Fuhrmann, it was widely believed due to the Rule of Drama that Maggie and Paxton would both be victims of the Decimation, so that Cassie would be Conveniently an Orphan. In the movie, though they don't physically appear, both of them were in the half that survived, making Cassie's teenage years only a little less rough.
A key component to a lot of speculation was that the plan would involve a timeline reset as a way of keeping future films consistent. However, while everyone's resurrected, the movie ends in 2023, with all of the dusted characters appearing as they did in 2018.
Going further, the fact that Feige once said that he wanted Spider-Man's movies to focus on him in high school, and that Far From Home took place after this movie with him in school, was seen as direct confirmation that everything would return back to normal. In the actual movie, it's established that everyone unsnapped returned as they were five years prior in 2023. Thus, Peter and his friends now attend high school in the early/mid-2020s.
On the opposite end though, some believed that the idea of Peter staying a high school student would be abandoned entirely, before the passage of time was even confirmed, if he survived at all, to the point that some speculated that Spider-Man: Far From Home was an entirely fabricated product meant to keep people from "discovering" that he'd be aged up or not be brought back to life at all.
Likewise, it was heavily speculated that the film's post-credit scene would somehow set the stage for the Fantastic Four or one of their related characters, such as Doctor Doom or Galactus. This didn't happen, and the creative team confirmed it was never really in the cards anyway due to the legal issues mentioned above.
A popular fan theory was that the time travel elements were actually all just a ruse, with any image suggesting it being dismissed as fake images or staged scenes meant to hide the true plot of the movie. In the end, Occam's Razor won out.
Katherine Langford was believed to have been cast as Kate Bishop once Disney announced her casting as an unnamed character after reshoots. Rumors especially kicked up once a Hawkeye show co-starring the character got announced. Turns out she was actually playing adult Morgan Stark and the scene got cut because test audiences thought it too confusing and repetitive.
There were several theories about Steve getting Mjölnir to budge in Age of Ultron and being able to pick it up here. One was that he could always actually pick it up then but didn't want to either upstage Thor (who at that point was more reliant on it emotionally than he is now) or ruin what was meant to a fun party game. Another was that he wasn't worthy at that specific point because something was weighing down his conscience, probably that he was keeping the fact that Bucky killed Howard and Maria Stark a secret from Tony. Another was that he was almost worthy but needed the events of the later movies to give him a push. The Russos and Kevin Feige would later confirm that as far as they're concerned, he was always worthy but didn't want to steal Thor's thunder.
After his death in Infinity War many were theorizing that Loki would end up pulling one of his old tricks. With one theory suggesting he took Bruce's place throughout Infinity War while the real Hulk was with the surviving Asgardians. This not the case on both accounts, the movie makes it clear that it really was Bruce the whole time and Loki the audience has been following since the original Thor did indeed die. But there is a bit of ambiguity regarding the Loki from 2012 that escaped with the Tesseract.
The Russo Brotherssaid that the title of the fourth Avengers film was not mentioned in the dialogue of Infinity War. Cue the first trailer revealing that Endgame is the subtitle, itself derived from a quote from Doctor Strange: "We're in the endgame now". Possibly a case of Flip-Flop of God, as rumors suggested that several titles were up for consideration.
The Russos also said that no characters from the TV shows would appear. Edwin Jarvis makes a cameo.
Angela Bassett said that Shuri survived the Snap. This movie shows that she was in fact killed by it. However, Bassett might have actually just been wrong instead of lying (many of the actors were actually given false information on who lived and who got dusted to minimize the chance for accidental spoilers; for instance, Chadwick Boseman was assured T'Challa survived Infinity War and it wasn't until he watched the movie at the premiere that he learned his character got dusted).
In the trailer, Natasha is seen practicing shooting at a target, but this scene is not included in the movie.
A scene with Thor in his Infinity War look holding Stormbreaker and powering up with lightning doesn't appear.
The Stinger of Captain Marvel, in which Carol appears before the Avengers asking for Fury, appeared to have been a clip from Endgamenote akin to the stinger of Ant-Man showcasing an edited clip from Captain America: Civil War. However, the scene does not appear in the film itself and Carol is instead introduced in a very different manner.
The scene from a trailer where Natasha sits outside of the Avengers compound while it's raining doesn't appear in the movie.
In the second trailer you can hear Thor saying "I saw all these people die", but he never says it in the actual movie.
In the second trailer, Tony and Steve shake hands after Tony asks "Do you trust me?" and Steve answers "I do." In the movie, they don't shake hands in this scene.
Real-Life Relative: Lila Barton is portrayed by Ava Russo, daughter of co-director Joe Russo. His other daughter, Lia, and Anthony Russo's son Julian appear in the scene where a group of children ask Professor Hulk for a selfie.
Refitted for Sequel: The opening scene with the Barton family was originally planned for Infinity War, but then Joe Russo decided to make it this film's first scene. The writers all felt that Hawkeye's character became more dramatically impactful after the snap whereas his arc in IW would have repeated beats from Civil War, i.e. a hero coming out of a 10-Minute Retirement.
Release Date Change: The original release date was May 3, 2019. However, following the success of the opening of Avengers: Infinity War in the last full week of April, Marvel opted to replicate that move here.
Most of the merchandise depicting War Machine's Mark 6 armor from the final battle (including the Marvel Legends version) got the colors wrong, showing the suit in black and silver instead of red, white and blue. Presumably, the production team's decision to use the Iron Patriot-inspired color scheme in the actual film was only made after the toy companies had already been given reference materials to base their products on.
Likewise, the majority of the action figures based on the Quantum Realm suits had them colored primarily gray/silver instead of white. Like the War Machine issue, this was likely a case of plans for the suits (which were created via CGI in post-production) changing after the toys had already been designed.
The toy line also spoiled the plot point about the Avengers using Stark technology to create a new Infinity Gauntlet.
Pepper's Rescue armor was also first revealed when a prototype of the Rescue action figure leaked online.
The focus on Thanos showing up primarily in his battle armor and wielding a double-bladed sword was spoiled by multiple toylines. However, most merchandise depicts him with the Infinity Gauntlet to conceal the fact that he's actually a time-traveling past Thanos.
Teasing Creator: Mark Ruffalo, known for accidentally spoiling stuff about these movies, went on The Tonight Show to share the title... Which was censored for the broadcast. Following this, he went all-out and described an action sequence which was almost entirely censored while he hammed it up on the stage.
In the script, Tony performed his Heroic Sacrifice in complete silence. Just a few months before release, the Russos figured that a character known for constantly quipping should say something at that moment, and it was editor Jeff Ford who had the obvious-in-retrospect idea of making it a retort to Thanos's "I am inevitable" refrain that also tied into the famous final line of the first MCU film.
The Downer Ending to Avengers: Infinity War was originally going to be this film's Downer Beginning; had that been the case, Infinity War would have ended with Thanos completing the Infinity Gauntlet before actually using it in this movie. However, the creative teams working on the two films decided that it best suited the story to have the actual Cliffhanger follow the Badass Fingersnap itself and to show its fallout before making viewers wait a year to see how the story would be resolved.
The first draft of the script had the characters avoid going back to the events of the first Avengers film and included Tony going with Thor and Rocket to Asgard to collect the Tesseract from Odin's vault (and getting into a fight with Heimdall in the process). A heist in the Triskelion and raiding the Sanctum Sanctorum interiors with its famous Escher-like geometry was also considered, as writers were hesitant about revisiting The Avengers, but ultimately it made both logical sense to do it at that point, and also in terms of audience familiarity.
Jane Foster was originally going to play the role of the person who pep-talks Thor out of his funk since Natalie Portman was willing to return now, but it was ultimately decided that it would make more sense to give that role to Frigga, since being Thor's mother and it being the point in time where she was to die makes her playing this role much more emotional.
There were plans for the present day Thor to fight his slimmer, more muscular self from The Dark World during the Asgard sequence, but that battle was dropped in favor of the similar fight between Captain America and his 2012-era self.
The Dark Elves from The Dark World almost returned as part of Thanos's army.
At one point, Christopher Markus and Stephen McFeely considered having Hank Pym and Janet van Dyne participate in the final battle with their old Ant-Man and Wasp suits.
Per Joe Russo, 2014 timeline Thanos and Ebony Maw were able to figure out how to synthesize Pym Particles and subsequently mass-produce them in order to make the jump into the prime timeline.
The Russos stated that Steve was always worthy of Mjölnir, and just didn't pick it up until now because it would have made Thor feel less special. Kevin Feige later confirmed this in an AMA on Reddit as well.
Word of Saint Paul: Yvette Nicole Brown has named her character, the woman in the elevator at Camp Lehigh in the 1970s, Phyllis, and Phyllis is a real S.H.I.E.L.D. agent, not a HYDRA agent.
And the working title used to hide the production was Mary Lou 2 (Infinity War was titled Mary Lou).
More specifically, arguably the most spoiler-heavy scene in the movie — the funeral of Tony Stark — was listed as "The Wedding" in all the information given to actors until time came to actually film it.