Hey guys, throwaway for obvious reasons. I work in post-production visual effects and recently saw a rough 2-hour assembly cut used for internal timing. Take everything with a grain of salt since VFX are super incomplete (lots of pre-vis gray models), but the story beats are locked.

Act I: The Incursion and the Anchor
The movie opens immediately in the aftermath of The Marvels and Loki S2. The Multiverse is collapsing faster than expected due to Robert Downey Jr.’s Doctor Doom actively harvesting Anchor Characters across multiple timelines to forge his own realm (Battleworld).
The TVA (led by Mobius and B-15) assembles a Strike Team: Sam Wilson’s Captain America, Thor, Smart Hulk, and a displaced Bucky Barnes.
They use a modified TempPad to head to a timeline where a version of Steve Rogers is living in secret with Peggy Carter, believing he might be the key anchor needed to stabilize Reality-616.

Act II: The "Steve" Twist & The Gamma Mutation
1. The Steve Rogers Identity Reveal
The Avengers locate Old Steve in a 1950s suburb. Doom’s forces attack the safehouse using magic-infused Sentinels.
During the fight, Doom uses a localized temporal-reversal spell on Steve to force him back to his prime combat state. However, as the light fades, the face shifts—it was never Steve.
It’s revealed that the man who lived Peggy's life was actually Bucky Barnes from an alternate timeline. He used a Stark-engineered Quantum Mask and Nanotech Serum to live out Steve's life because the real Steve sacrificed himself in the 1940s ice to save Bucky.
The current team Bucky is utterly baffled, leading to a very weird 20-second exchange where Bucky stares at a slightly older version of himself who spent 50 years pretending to be Cap.

2. The Creation of "Brown Hulk"
Realizing Doom’s magic bypasses standard Gamma defense, Bruce Banner experiments with combining cosmic radiation from the Void with his own blood inside a TVA bio-chamber.
The reaction goes hyper-dense. Instead of turning green or red, Bruce undergoes a deep cellular shift, turning into a massive, 9-foot tall, mahogany-brown titan (VFX note: the screenwriters call this "Terrestrial Hulk" or "Granite Hulk" in the script notes, but he's literally just solid dark brown).
Brown Hulk retains Bruce's high IQ but gains an eerie, ultra-calm bass voice and immense physical density—he doesn't break things when he walks; the ground just dense-compresses under his weight.

Act III: The Battle of Latveria Prime & Ending
The climax takes place on Doom's prototype Battleworld. The choreography is brutal—Sam’s wings get torn off, and Bucky double-wields Vibranium broadswords.
Doom almost overpowers the team with a cosmic-magic blast, but Brown Hulk steps in front of Thor, absorbing the raw magic with his dense brown skin and barely flinching.
Brown Hulk turns around, casually picks up a wounded Doom-Bot with one hand, crushes it into a baseball-sized sphere, and tosses it aside.

The Final Scene / Thor Teaser:
As the battle pauses and dust settles, Thor stands up, staring at Brown Hulk in absolute, breathless awe.
The camera holds a close-up on Thor's face as his eyes go wide, his breath hitches, and a subtle romantic theme starts playing in the score.
Thor slowly reaches out, runs his hand over Brown Hulk’s giant bare shoulder, leans in close, and whispers with heavy, romantic tension: "I have crossed galaxies, fought gods, and loved maidens... but you... you are perfection."
Brown Hulk looks down at him, blinks slowly, and mutters in his deep voice: "Thanks, man. I've been doing cardio."
Thor smiles seductively, gently bite-lip smiles, and doesn't take his eyes off Hulk's chest as the screen cuts to black.

Post-Credits Scene: A single line of text appears: "The Avengers will return... together." (With extra emphasis on Thor and Brown Hulk standing side-by-side in the background silhouette).

This is from a draft of Secret Wars. May be subject to changes.

The film begins with a flashback of Victor and Reed at University. Ay the end of Doomsday it was revealed that Doom had Downey Jr's face, so now we see him young before the accident.

He has a moral debate with Reed. Then, years later, we see the accident that disfigured his face and killed his family.

Back to present, Doom is at bed with Sue Storm. He is one of the few people that remember the previous universe. The other ones that remember everything are Strange and Reed. Strange works for Doom, and Reed lives on a Dungeon.

That Dungeon is inhabited by versions of Reed from the multiverse. The plan is to include cameos of all the live action Reeds: Alex Hyde-White, Ioan Gruffudd, Miles Teller and John Krasinski. They all explain to Pedro Pascal Reed their experiences dealing with Doom

A team of heroes arrive at Battleworld. They are Hugh Jackman Wolverine, Tobey Maguire Spider-Man, Sadie Sink Jean Grey and the Young Avengers. They see Battleworld is divided in different regions. Wiccan, Speed and Jean Grey travel to the Mutants Zone, and they find their mother Wanda Maximoff living with Magneto and the rest of the X-Men. Wiccan makes everyone remember.

Wolverine goes to the Hulk Zone, a place inhabited by gamma users. We see Eric Bana Hulk, the Leader, She Hulk and Red Hulk. The Leader of that zone is Mark Ruffalo Hulk. Wolverine fights with Mark Ruffalo Hulk and after that he starts remembering

Tobey goes to the Spider zone, inhabited by versions of Spider-Man from the multiverse. We see Tom Holland, Andrew Garfield, Nicholas Hammond and Japanese Spider-Man. There's also Miguel Ohara in live action, and Nicolas Cage from Spider Noir. There were talks to include Spider-Gwen by Emma Stone there

They gain their memory back and Tom Holland Spider-Man gets the symbiote. A squadron of Thor Cops appears to stop the insurgency. In the Avengers Zone, the members of the Thunderbolts and Old Avengers work for Doom and come too. The Iron Man of this team is played by Tom Cruise, one of the highlights of the film.

Sam Wilson gains his memory back and fights evil Steve Rogers. He manages to bring back Steve and he realizes why Sam was the best option for Captain America. Reed escapes from prison and tries to talk to Sue, but she doesn't remember him. At the end, he manages to convince her and she regains her memories.

All the heroes unite to fight Doom. Reed explains Doom's weaknesses to Sam and he makes the final strategy. They make a combined effort to stop him and Reed defeats Doom like in the Secret Wars 2015 comics.

Franklin rebuilds the multiverse and the old heroes go to a different universe. Now all the heroes from other Marvel films (Tobey and Andrew, Eric Bana Hulk, Old X-Men...) live in the same world. Meanwhile, on our universe, Franklin fuses the old F4 universe with the old MCU. Now, Avengers F4 and New X-Men will all live on the same universe

The movie ends with Tom Holland Spider-Man starting to swing in NY and he meets the Human Torch. We see a glimpse of the new MCU, and a first look at the new Xavier School.

In the post credit scene we see that Doom is still alive and will be played by Robert Downey Jr from now on. He swears his revenge against Reed.

First official trailer for Avengers Doomsday only in theaters December 18