Reshoots are often considered troublesome when it comes to big-budget filmmaking, but over the years, Marvel Studios has made them an expected part of the production process.
This allows the studio to make as many changes as they like and planning for them in advance means they're not lumbered with a movie that isn't working. After all, we've seen what happens when a production - 2015's Fantastic Four, for example - discovers it needs to somehow bring everyone back to fix with little to no notice.
It's a smart approach, albeit one which hasn't always paid off. Over the years, Marvel Studios has made sweeping changes to its movies, sometimes for the better and occasionally for the worse. We'll allow you to decide which category the alternate endings you read below should fall into but suffice to say, had these seen the light of day, the MCU as we know it would be unrecognisable.
To take a closer look at what might have been, click on the "Next" button below.
5. Avengers: Endgame
Avengers: Infinity War and Avengers: Endgame both went through major changes during production; for example, The Hulk initially returned at the end of the 2018 movie, bursting out of the Hulkbuster armour before being overpowered by Thanos.
However, concept art for the 2019 finale to the Infinity Saga reveals Tony Stark was once set to be there when Steve Rogers travelled back in time to return the Infinity Stones to their rightful place in history.
This may have been a misdirect or an indication that Iron Man wasn't always destined to die during Avengers: Endgame's final battle. If we assume it was the latter, then who knows how different the MCU would have liked moving into the Multiverse Saga (even if he'd retired, Tony was surely set to remain a major player).
As things stand, we expect Marvel Studios to throw as much money as it takes at Robert Downey Jr. to return as a Variant in the next Avengers movies!
4. Thor: The Dark World
Thor: The Dark World once had a completely different ending and it appears the entire thing was reshot when Marvel Studios changed its plans for the God of Thunder.
The hero was set to wake up on Earth where his father was waiting for him; after the hero had spent the past few days unconscious, Odin got to know Jane Foster during that time, realising Thor was right to fall for the human woman. As a result, the King of Asgard apologises to his son.
Unfortunately, Jane has decided she can no longer be with Thor due to their respective commitments. The hero attempts to change her mind but ultimately realises he must do his duty and returns to Asgard where he chooses to rule in Odin's place as King.
So, Loki was set to remain dead, Thor would be King of Asgard, and Odin was set to go off and do his own thing. There's no way Avengers: Age of Ultron, Thor: Ragnarok, and Avengers: Infinity War were going to look the same after these plot developments.
3. Avengers: Age of Ultron
Avengers: Age of Ultron was always going to end with Captain America and Black Widow assembling a new team of Earth's Mightiest Heroes. However, Joss Whedon hoped to introduce at least one major character in this sequence.
That was Captain Marvel and the stand-in above was used while Whedon attempted to figure out who could play her. Marvel Studios and Kevin Feige had other ideas, though, and later replaced Carol Danvers with the Scarlet Witch (much to the filmmaker's chagrin).
Had Whedon got his own way, Captain Marvel would have made her MCU debut four years before her solo movie was released. Whedon casting someone other than Brie Larson is likely - the actress above was a stand-in - but the hero's story was likely set to play out much differently.
Whether you agree with Whedon or Feige on this one, it's hard not to wonder about what might have been.
2. The Marvels
In The Marvels' closing moments, Monica Rambeau used her powers to close a tear in reality, stranding herself in a parallel universe inhabited by the X-Men. However, an earlier version of the movie saw Photon receive a helping hand from Carol Danvers and Ms. Marvel.
It appears the trio would have fixed that tear in reality, likely meaning the Captain Marvel sequel didn't always feature a Multiversal component.
That was confirmed by concept art, not to mention a recent behind-the-scenes photo showing Iman Vellani's Kamala Khan in a space helmet. However, Dar-Benn actress Zawe Ashton has since revealed a version of the movie which wrapped up with the villain and Carol combusting in space together!
It seems The Marvels was going to end with Captain Marvel believed dead, and while we're sure she'd have eventually returned, it's possible this was once meant to serve as Brie Larson's farewell to the role. That's huge.
1. Ant-Man and The Wasp: Quantumania
Marvel Studios reshot Ant-Man and The Wasp: Quantumania's ending weeks before the movie arrived in theaters. However, in an earlier cut, Scott Lang and Hope Van Dyne were going to don new, hi-tech costumes for the final battle with Kang the Conqueror.
Just like in the theatrical cut, Janet, Hank, Cassie, and Hope all returned to Earth, only for Scott to be confronted by a vengeful, battle-damaged Kang. They fight, but the villain escapes even after The Wasp returns to lend Ant-Man a helping hand. With that, they're left trapped in the Quantum Realm just as Janet once was.
Cassie would have continued searching for her father, but with Kang on the loose - and M.O.D.O.K. if previous leaks are accurate - Earth-616 was going to be facing two major threats heading deeper into the Multiverse Saga.
With Jeff Loveness then tapped to write Avengers: The Kang Dynasty, he was clearly setting the stage for that movie. Marvel Studios seemingly had other ideas.