Thanos dies to Thor before the opening credits, but he has already destroyed the stones. The rest of the movie centers around using the Quantum Universe to retrieve the stones from the past timeline.
Natasha and Clint go to retrieve the soul stone, with Clint sacrificing Natasha to access it.
Stark builds a gauntlet to wield the retrieved infinity stones to reverse the snap.
Banner has become Hulk permanently, but retains his intelligence and memories as Professor Hulk.
Scott, Hulk, Steve, and Tony travel to the battle of New York to retrieve the mind, space, and time stone. Steve fights his past self.
Thor is living with Korg and Miek, getting drunk and not caring about what happened. Hulk and Rocket go to get him, and his beard and hair are messy and grown out.
Hulk tried to wield the Stark gauntlet, but it appears to be too powerful for him.
Steve dual wields his shield and Mjolnir, it’s unclear how mjolnir comes back. Thor still has Stormbreaker, possible meaning he’s become unworthy due to him neglecting his duties.
Sam is the first dusted avenger to come back, we hear him say to Steve “On Your Left,” then we see T’challa and Shuri coming out of a portal, and Sam flying out.
Big scene with all the Avengers, including Wasp, the Guardians, Spider-Man, vs Thanos and a revived Black Order. It looks like the big fight in Ready Player One, but we actually care about the characters
Stark reunites with Peter and gives him a hug
Carol gets the short hair she has in recent comics, and Peter Parker gives her the Stark Gauntlet