Five Years Earlier
After pulling the Mind Stone out of Vision's forehead, Thanos places the last Infinity Stone in his gauntlet. The energy surge is much more than any previous - his torso is wreathed with iridescent static and he bellows from the sensations.
As Thanos studies the completed gauntlet, a massive bolt of lighting strikes him, digging him into the ground and grinding him back for meters. Thor has arrived, eyes glowing with power, stooping down from the sky like a bird of prey. The God of Thunder pauses his attack, reverses his position, raises Stormbreaker above his head and hurls it - Thanos fires the whole might of the gauntlet against it, but it only creates a rainbow-like bow-shock, not slowing the ax as it slams right into Thanos' chest.
Thor: [Lands in front of Thanos, who is down on one knee; hatefully.] I told you. You'd die for that!
He takes hold of the back of Thanos' head and forces Stormbreaker deeper into his chest, staring angrily into his eyes while Thanos cries out in pain]
Thanos: [Weakly] You should have... you... [suddenly stronger] you should have gone for the head! [He raises his gauntlet and snaps his fingers.]
Thor: NO!
The gauntlet activates a blinding flash of energy after the Mad Titan snaps his fingers. It cuts sharply to a view of Thanos his hand on his chest, no wounds visible. Thanos now seems to be inside a vast orange void called the Soulworld, which is inside the Soul Stone, where he sees a young Gamora and the pavilion from the home world of the Zen-Whoberi.
Thanos: Daughter?
Gamora: Did you do it?
Thanos: Yes.
Gamora: [Beat] What did it cost?
Thanos: [Solemnly] Everything.
Now out of the Soul World, Thanos is snapped back to normal reality, and notices the damage inflicted on the gauntlet - the metal scorched and distorted from heat, the stones no longer glowing.
Thor: What'd you do? [Angrily] WHAT'D YOU DO?!
Thanos nearly seems to not notice Thor before he uses the Space Stone and teleports away, leaving Stormbreaker behind on the ground.
Captain America: [Stumbles into the clearing, holding his left side] Where'd he go? Thor... where'd he go?
Bucky: Steve?
He looks at his prosthetic arm before stumbling over, and collapses into ashes, much to Cap's shock; he walks over and touches the ground where Bucky's ashes evaporated disbelievingly. Thor also looks in shock too.
On the battlefield, Wakandan soldiers disintegrate to ashes, much to M'Baku's horror.
Black Panther: [While reaching for a fallen Okoye] Up, General. Up! This is no place to die. [The Wakandan King holds out his hand for his bodyguard. He suddenly disintegrates into ashes and, in anguish, Okoye falls back on the ground.]
She gets up on her feet after seeing her king vanish into thin air.
Okoye: (shocked) Kumkani?!
Groot: [Slowly corrodes into ashes as well by Rocket] I am Groot...
Okoye: Kumkani?!
Rocket: No... no. No. No. No! (sees him disappear) Groot, no...
Scarlet Witch is mourning over Vision. She then turns into ashes. An injured Falcon turns to ashes, hidden in the long grass.
War Machine: [Searching for Sam, missing him by only a few feet] Sam? Sam!? Where you at?!
Titan
The remaining members of the Guardians and Avengers collect themselves - Mantis props up Star-Lord, Spider-Man helps Tony to his feet, Drax and Nebula manage to limp over on their own.
Mantis: Something's happening. [She disintegrates into ashes.]
Drax: [To Quill as he dissolves] Quill?
[Quill stares in horror.]
Tony: [Staring panicked at the slowly fading Quill] Steady, Quill.
Star-Lord: Aw, man. [Quill also gets disintegrated into ashes]
Doctor Strange: [Calmly turns to Stark] Tony, there was no other way. [He finally gets erased.]
Spider-Man: [Realizes he's fading away] Mr. Stark? I don't feel so good...
Tony: [Trying to be calm, his voice shaking as he looks at Peter in terror] You're all right.
Spider-Man: [Stumbling and terrified] I don't know what's - I don't know what's happening. I don't- [He falls into his mentor's arms, clutching him tight while beginning to cry.] I don't wanna go, I don't wanna go, Mr. Stark, please. Please, I don't wanna go. I don't wanna go... [There is a short silence before Peter speaks again] I'm sorry. [Parker disintegrates into ashes in Stark's arms.]
Tony falls forward from the lack of weight in his arms, before staring at his hands in disbelief.
Nebula: [To Tony Stark, seeing Thanos' victory.] He did it.
Stark mourns silently at their failure. After seeing the others decompose into thin air, leaving him and Nebula alone on Titan.
Back on Wakanda, the remaining team members, Captain America, Thor, War Machine, Black Widow, Bruce Banner, and Rocket are left mourning near Vision's dead body. Captain America turns over Vision's bleached corpse as Black Widow runs up to the other survivors.]
War Machine: What is this? What the hell is happening?
Captain America: [Pause] Oh, God.
Meanwhile, in a different place, in a rustic house on a terraced slope with a scarecrow made of discarded armor, Thanos sits down and watches the sun rise.
Atlanta, day
While driving on the streets of Atlanta, Nick Fury and Maria Hill were trying hear any update on Stark's location, which they have nothing.
Fury: Still no word from Stark?
Hill: No, not yet. We're watching every satellite in both hemispheres, there's still nothing. [Receives three beeps from her device.]
Fury: What is it?
Hill: Multiple bogeys over Wakanda.
Fury: Same energy signatures as New York?
Hill: Ten times bigger.
Fury: Tell Klein. We'll meet him at- -
Hill: Nick! Nick! [A car spirals out of control in front of them. They get out and Hill checks on the passengers.]
Fury: They okay?
Behind their vehicle, a motorcycle lies in the middle of the street with a concerned citizen approaching it.
Hill: There's no one here.
They hear helicopter rotor sounds from the direction they'd come, but it sounds wrong, spinning out of control, its tail rotor smoking from damage already, appears and crashes nose-first into a building. Screaming intensifies. The two are now witnessing civilians around them suddenly disintegrating.
Fury: Call Control. Code Red.
Hill: Nick?
Fury turns around to see Hill disintegrating.
Fury: Hill?
Fury then races back to their car and gets a what appears to be an old pager with extra gear attached out of his bag on the back seat. He sends out an emergency alert, mere seconds before his hand turns into ashes.]
Nick Fury: Mother...
Fury corrodes to dust. The pager falls to the ground, red lights blinking on the additions; the camera zooms in and we see the device display "SENDING..." then display a red-blue-and-gold star insignia - the symbol of Captain Marvel.
San Francisco, day
On a rooftop of a parking lot, Dr. Hank Pym and his wife Janet van Dyne are working side-by-side prepping an experiment.
Hank: I used to be a respected scientist. Had my name on the sides of buildings. Now, I got this.
Janet: You wanted a smaller Quantum tunnel. This is smaller.
Scott accidentally honks the horn of Luis' Van, which it goes off.
Scott: Oops, sorry! My bad!
He steps out of the van.
Janet: I think it has some flair.
Scott presses a button that activates the Portable Quantum Tunnel.
Scott: All right. The controls are online.
Hank spins the dial to activate the Quantum Tunnel.
Hope: The collection units activates when you decouple it. It should automatically start absorbing quantum healing particles.
Janet: Also, make sure you stay out of the Tardigrade fields. They're cute, but they'll eat you. And don't get sucked into a Time Vortex. We won't be able to save you.
Scott: Mhm hmm!
Hope: Okay! Going subatomic in five... (Scott puts on his mask) four... three... two... one!
She pushes the lever and Scott enters the Quantum Realm.
Hank: All right, Scott. This is mic check!
The trio know what Scott is doing.
Scott: Mic check! One, two! One, two! How's everybody doing tonight in the Quantum Realm?
Hank: Scott, we read you.
In the Quantum Realm
Scott: I just want to make sure.
He opens the container to collect the healing particles before closing it.
Scott: Okay. Healing particles secured for our new ghost friend.
Hope: Great. Preparing for re-entry in, five... four... three...
As the comms go static when Scott was about to get out of the Quantum Realm.
Scott: Hello? Ha ha! Very funny. Hank, quit screwing around. You told me yourself not to screw around. (Back at the parking lot, Hope, Hank, and Janet disappeared due to Thanos using the powers of completed Infinity Gauntlet.) Hank. Hope? Janet! Guys. Guys! Okay, seriously, don't joke around, bring me up, let's go! Guys?!
Scott's House
The sound of the emergency broadcast system was heard on TV, which Scott forgot to turn off. However, one of Hank's big ants survived the Snap, playing the drums, not knowing that Scott is in the Quantum Realm.