Forest area, day
Near the wreckage of the New Avengers Facility, the smart ones turn out to be Bruce, Tails, Lisa, Sandy, and Don began building a similar quantum tunnel, which is a small version of the original that was destroyed after Thanos' attack.
Sandy: Well that's about done!
Tails: Good to go!
Lisa: On the contrary! We need to do something about the Infinity Stones! At least there will be a temporal paradox could change the time-space continuum. Street name: Alternate timeline.
Don: Exactly, Lisa! Maybe one of our friends could handle that kind of situation before everything could change.
Bruce: It's like the Ancient One told me that the stones would be back in its original timeline where it never left. And they will remain that way.
Tails: Come to think of it! Loki must have escaped with the Tesseract to avoid going to the Asgardian prison.
Sandy: Not if we can help it!
She shows them a tracking device and an electronic bug.
Don: Good idea, Sandy! We need to bring our friends here right now!
10 Minutes Later
Moments later, Bruce opens up a briefcase to reveal the six Infinity Stones as Steve volunteered to return them along with Mjolnir, to their respective time periods. He met up with Bruce, Sam, Bucky, Tails, Sandy, Lisa, and Don where a new time machine was
Bruce: Remember, you have to return the stones to the exact moment you got them. Or you're gonna open up a bunch of nasty alternative realities.
Steve: Don't worry, Bruce. Clip all the branches.
Bruce: (looks sad) You know, I tried. When I had the gauntlet, the stones, I really tried to bring her back. I miss her, man.
Tails: It's gonna be all right, Dr. Banner!
Sandy: She was a great person!
Steve: Me, too.
Sam: You know, if you want, I can come with you.
Steve: You're a good man, Sam. This one's on me, though.
Steve goes over to Bucky.
Steve: Don't do anything stupid 'till I get back.
Bucky: How can I? You're taking all the stupid with you.
Sandy & Tails: Huh!?
Bucky: I meant him!
Sandy: Oh!
Tails: Not what we had in mind.
The World War II veterans both hug each other
Bucky: Gonna miss you, Buddy.
Steve: It's gonna be okay, Buck.
Steve goes over to the Quantum portal and dons the Quantum suit.
Sam: How long is this gonna take?
Bruce: For him? As long as he needs. For us? Five seconds.
Steve picks up Mjolnir.
Bruce: Ready, Cap? Alright. We'll meet you back here, okay?
Steve: You bet.
Bruce: Going quantum. Three, two, one -
Before he would send Steve back in time to return the stones and Mjolnir to their proper time periods, Sonic, Shadow, and SpongeBob suddenly arrive.
Sonic: Wait! Hold up!
SpongeBob: Cap, wait! You forgot about the other items.
He shows him the magic book that he and Plankton took from 2015. Sonic has Caliburn he took from the 12th Century.
Shadow: At least we need to put the stones back in their natural containments.
As the three showed them the containers for the stones which included the Scepter, Tesseract, and the Orb for the Mind, Space, and Power Stones in order to return them to their primary states.
Steve: I've decided for you to come along in order to restore the timeline.
Sonic: Sure thing, Captain! I've got the scepter for Mind Stone.
SpongeBob: I got the orb for the Power Stone. However, the purple rock is very intensely hot.
Lisa: Actually it's gamma radiation to be exact.
SpongeBob: I get it!
Sandy: (gives him the tongs) In case if you touch the Power Stone, you'll burn!
He nods with agreement.
Shadow: I used Chaos Control to rebuild the cube for the Space Stone to be put back in place. With the assistance from the Time Stone.
Silver suddenly arrives with the Aether Extractor for the Reality Stone.
Silver: Sorry I'm late! But I have the Aether Extractor for the Reality Stone. But it has to liquify once again in order for it to get back inside Jane Foster's body.
Sonic: Good thinking, Silver! Let's get to it!
Sandy: Mind if I come along?
SpongeBob: Sure thing, Sandy!
Tails: Don't forget about this.
He gives Steve and Sonic a tracking device and an electronic bug which could help locate Loki.
Sonic: Tails, come join us!
Caliburn: Tag along!
Tails: All right!
He reluctantly joins them before he, Sonic w/ Caliburn, Shadow, Silver, SpongeBob, and Sandy activate their Quantum Suits. Five seconds later, they shrink down into the tunnel to the quantum realm before splitting up to where the previous teams left.
Morag, 2014
Moments later, Steve, Sonic, Shadow, and SpongeBob grew back to normal size as they came near the area where the orb was kept.
SpongeBob: (pulls out the orb) OK, I got out the orb!
Steve: (opens the case) Let's do this!
Sonic: Here goes nothing!
He gets the tongs to grab the Power Stone to place it back in the orb just before the blue hedgehog puts it back in the force field where Rhodey, Raph, and Nebula obtained the stone.
Shadow: Well that takes care of that. Now to fix the timeline.
As he grabs the Time Stone from the case as it is floating above his hand. As he concentrated hard and used the Time Stone to make things go back to where they were. All of a sudden, a bright green flash, making the guys shield their eyes.
Sonic: That seems awkward.
Shadow: Yeah, I was able to fix. But this timeline will play out as it does in the future.
Steve: Let's take the Soul Stone back to Vormir where it came from.
SpongeBob: Sandy's in 1970 with the Tesseract. (to Steve and Shadow) I'll meet up with you in 1970!
Sonic: And Silver's in Asgard of 2013, with the Aether Extractor. (grabs Mjolnir from Steve's hand) Meet up with us soon!
Steve: Got it.
The yellow sponge and the blue hedgehog activate their Quantum Suits to shrink to the quantum realm to 1970 and 2013.
Shadow: Good luck with that! (turns to Steve) I'll take us there! (reaches out his Chaos Emerald) Chaos Control!
A flash of light surrounds them by teleporting them Vormir. Moments later, Quill came into the area to get the orb.
Vormir, 2014
As both the First Avenger and the Ultimate Life Form appeared next to the summit of the mountain where the shrine is located.
Shadow: Well that seems oddly unfamiliar!
Steve: Now let's see what's up there!
Familiar Voice: Welcome, Shadow the Hedgehog, creation of Gerald Robotnik!
Shadow: Who's there? Show yourself!
Steve: Wait! I know that voice! It's the Red Skull!
Red Skull: Captain America! We meet again!
Steve: I saw you disappear when the Tesseract destroyed you.
Red Skull: Unfortunately, it cast me out here to guard the stone until my release.
Shadow: Hmph! That's not how Chaos Control could work like that.
Red Skull: I sense that you've come to return the Soul Stone!
Steve: Yes! But if we clash next time! Just remind me! I'll be waiting!
He opens the case before handing his nemesis the orange Infinity Stone.
Red Skull: Very well! We will fight again one day!
Shadow: That takes care of that! Let's go!
They activate their Advance Tech Suits and shrink to go to 1970.
New Jersey, 1970
In the military installation, Steve and Shadow met up with SpongeBob and Sandy in the room where the Tesseract was kept.
Steve: Got the cube?
Sandy: Yup!
SpongeBob: (opens the safe) Ugh! The safe is open! Now place the stone there!
The captain did as he does right before the safe door closes.
Shadow: Now let's fix this timeline.
He uses the Time Stone to fix the bars in the safe that Tony used his iron glove to cut them to open the safe like he did earlier.
SpongeBob: Glad we got that straighten out!
Shadow: Now we go to Hank Pym's lab where his creations were made.
SpongeBob: Well Sandy and I have to put the book back to where it came from before the Great Krabby Patty Famine will occur.
Sandy: That's right! We're going to 2015 right before Burger Beard will get his hand on it.
Steve: Good luck you two!
They nod right before activating their suits to time travel to 2015.
Shadow: Shall we?
Steve: Got it!
They teleport to Hank Pym's lab right where Steve took four vials from earlier when he and Tony manage to obtain the Space Stone after Loki escaped in 2012.
Steve: Here we go! (puts back the other vials)
Shadow: (pulls out the Time Stone) Hmph!
He reverses time in order to fix the timeline right before a young Hank Pym appears when he heard Steve on the phone pretending to be Captain Stevens from shipping. Unbeknownst to him, Shadow and Steve are hiding behind a booth until Shadow puts the green stone back in the case.
Steve: (quietly) That's done!
Shadow: (also quiet) Let's go!
They activate their suits to shrunk before the young doctor hears something.
Young Hank Pym: Huh?! Oh! (gets back to work)
Asgard, 2013
After materializing right where they will meet Sonic and Silver in the corridors of the palace to find Jane Foster's chambers.
Silver: There it is! Jane Foster's room!
Sonic: All we have to do is get the Reality Stone back inside her and things will turn out fine.
Shadow: Now let's get this over with! (holds up a Chaos Emerald) Chaos Control!
As Shadow freezes time before opening the door to the woman's room, whom the latter was frightened after Rocket, Silver, and Jet showed up.
Steve: Got the needle?
Silver: (reveal the extractor) Sure thing!
As Steve opens the case, Silver uses his psychokinesis to transform the Reality Stone back to its liquid state before putting it in the extractor.
Shadow: Better hurry it up before Chaos Control wears off in a few seconds.
The psychic hedgehog did as he injected the human woman with the Aether back in her body.
Silver: I guess that's done!
Sonic: Now I'll put Mjolnir back to where it came from in the palace.
He threw the hammer right in the hall where the doors of 2013 Jane's room is.
Steve: Let's go! Tails has the scepter in 2012.
Sonic: Right! I'll meet up with you after I drop Caliburn off!
Caliburn: I'm going to miss you, Sir Sonic!
Sonic: Me too, pal!
As he activated his suit and shrank to the quantum realm to the 12th Century.
Shadow: Now let's get to Tails before time runs out!
They nod right before putting on the suits and shrank to 2012 just moments before Chaos Control wore off and 2013 Jane unfroze before she got confused.
Grand Kingdom, 12th Century
Sonic and Caliburn arrived back right where they left moments after departed.
Sonic: So long, Caliburn!
Caliburn: Until we meet again, Knight of the Wind!
The blue hedgehog places the sacred sword back in the garden of the castle ruins before suiting up to shrink to 2012 New York City.
Bikini Atoll, 2015
After materializing, the sponge and the squirrel trek through the jungle area of the island. However, Sandy begins to notice Burger Beard's ship.
Sandy: SpongeBob! Burger Beard at 12 o'clock as he approaches here in a few minutes!
SpongeBob: I know, Sandy! But we made it just in time to put this back to its holder.
He immediately hands the magic book to the skeleton.
SpongeBob: Mission accomplished! Now we head back to the present.
Sandy: Good idea!
They activate their Quantum Realm Suits to shrink back to 2023 just moments right before the pirate makes his arrival on the island.
New York, 2012
After meeting up with Tails in the lobby of Stark Tower, Steve and the two hedgehogs notice the agents just before seeing Tony as an agent, and 2012 Tony and 2012 Thor arguing with 2012 Alexander Pierce while 2012 Loki watched.
Sonic: That's what happened.
Tails: Yes! Loki managed to escape from S.H.I.E.L.D. and created a new timeline.
Shadow: I think we're about to find out what happens next.
Steve: Got the electronic bug, Tails?
Tails: Yeah!
Soon as the fight begins to intensify right before the two-tailed fox started flying above the agents and the 2012 versions of Thor and Tony Stark until he spotted 2012 Loki before throwing the tracking bug on the God of Mischief's back.
Shadow: And now we wait for the right time.
Steve: Okay, now we must get to the point where Loki disappeared.
The heroes witness the fight nearly starting to break out.
2012 Pierce: I need the case.
Both Tony and Knuckles witness the situation starting to heat up really quickly.
Tony: Do it, Lang! Window's closing. Pull my pin!
Knuckles: Come on!
Scott: Here goes!
Ant-Man pulls the pin of 2012 Tony's Arc Reactor, which cause past Tony to suffer a cardiac arrest drops the case. The guys are concerned for past Tony.
2012 Pierce: Stark?
2012 Thor: Stark?
Past Tony falls down to the floor.
Operative: He's convulsing. Give him air!
2012 Pierce: Medic!
Tony: Medic! Give these guys some help.
Sonic: It's lucky that Tony's heart is artificial.
Steve: Indeed!
2012 Thor: Speak to me. Stark, is it your chest machine?
Ant-Man kicks the case, Loki sees it moving until Tony grabs the case just in time.
Knuckles: Well that did the trick. Okay, let's go!
Tony: Good job. Meet me in the alley. I'm gonna grab a quick slice.
Suddenly, 2012 Hulk pushes Tony to the ground before the case starts to open and the Tesseract slides to Loki's left foot.
2012 Hulk: NO STAIRS!
Everyone runs from Hulk's rampage.
Shadow: So that's what happened.
Steve: We should've remembered Hulk's interference.
Sonic: And here it goes!
Knuckles witnesses 2012 Loki grabbing the Tesseract in order to escape from S.H.I.E.L.D. and the 2012 Avengers.
Knuckles: No! Loki took the Tesseract and got away.
Operative: Come on, Stark, stay with us!
2012 Thor: I'm going to try something, okay? I have no idea if it's gonna work.
2012 Thor uses the Mjolnir as the defibrillator on 2012 Tony.
2012 Thor: YES!
2012 Tony: That worked a treat. That was so crazy!
2012 Thor: I had no idea if that was gonna work.
At that moment, Sonic slid the tracker over to the agents and the 2012 versions of Tony and Thor.
2012 Tony: The case?
2012 Thor: The case is, uh... Where's the case? (noticing his brother is gone) Where's Loki? Loki!
Elsewhere, Knuckles joins both Tony and Scott.
Scott: That wasn't supposed to happen, was it?
Tony: Oh, we blew it.
Knuckles: And Loki just stole the Tesseract which has the Space Stone in it.
2012 Thor: Loki!?
Moments later, 2012 Tony noticed the tracker on the floor.
2012 Tony: (he picks it up) What's this?
2012 Pierce: It looks like a tracker.
2012 Tony: But what's it tracking?
2012 Thor: It must be Loki. We must find him.
2012 Tony: Then let's go!
Sonic: I think that's our cue.
Steve: Let's go!
Shadow: (turns to Tails) Got the scepter, Tails?
Tails: (show the scepter) I sure do! Let's get to the elevator!
They bolted to the elevator.
Several floors up, the heroes arrived on the floor 2012 Steve was lying unconscious.
Sonic: Now let's the Mind Stone back in the scepter right before erasing Rumlow and Sitwell's memories from the elevator.
Steve: Got it!
Just as the captain opens the case to get the yellow Infinity Stone before Tails pulls out the scepter and opens the coating before Steve puts the stone inside until he closes the coating. Moments later, Steve puts the scepter back in the case before closing it.
Steve: (picks up the case) All right! Just one stone left! We have to erase the S.T.R.I.K.E. team's memories just before giving them the scepter in the elevator.
Shadow: Now let's restore the timeline! Chaos Control!
As time freezes, Shadow grabs the Time Stone before rewinding 2012 Steve of his memories about what happened from the fight with his future self.
When the S.T.R.I.K.E. team is outside the tower when 2023 Steve said about hailing HYDRA earlier in the elevator. However, the heroes arrive with the case containing the scepter before giving it to Rumlow. Secondly, Shadow uses the green stone to erase the STRIKE team's memories from earlier.
Shadow: (puts Time Stone back in the case) Well that's done. Now we have to give this to the Ancient One.
Just as Chaos Control wore off, time goes back to normal.
Sonic: Let's go!
The black hedgehog nodded as he teleported himself and his allies to the Ancient One's location.
Sanctum Sanctorum, day
Moments after Bruce left, the Ancient One hesitates before noticing Steve, Sonic, Shadow, and Tails in front of her to give her the Time Stone and she places it back into the Eye of Agamotto.
A.O.: Well that went fast.
Steve: Yeah!
Sonic: But not as fast as it should be.
Tails: I've heard a lot about you! You're the Ancient One, right?
A.O.: Why yes I am! Say, you know Knuckles, the guardian of the Master Emerald on Angel Island?
Tails: Sure did!
Shadow: I guess it's all clear now.
A.O.: (turns to Shadow) By the way, I have heard about the alien invasion a couple years ago until you defeated Black Doom, right?
He nods.
A.O.: And you must be Sonic the Hedgehog, the Fastest Thing Alive?
Sonic: Yeah!
A.O.: And you must be Captain Rogers? You've been frozen in ice for 70 years after the war?
Steve: I sure am! But I'm planning to return to see the woman I love, Peggy Carter!
A.O.: It's been nice knowing you, guys!
They all wave goodbye before activating their Advance Tech Suits to shrink to the quantum realm.
Present day
The others are at the Quantum Tunnel waiting for their friends to return.
Bruce: And returning in, five, four, three, two, one!
Only Sonic, Shadow, Tails, SpongeBob, and Sandy except Steve and Silver, who had gone back to 1945 and 2223.
SpongeBob: Whew! That was one epic mission for putting the stones away.
Sonic: Hey, guys! We're back!
Sam: Sonic, where's Cap and the white hedgehog?
Sonic: Well Silver had to return to the future!
Sam: Yeah but, where's Cap?
Everyone was confused. Except for Sonic
Bruce: I don't know. He blew right by his time stamp. He should be here.
Bucky turns around from the pad. Sonic turns to him as well.
Sam: Well, get him back.
Bruce: I'm trying.
Sam: (concerned) Get him the hell back!
Don: Sam, calm down!
Bruce: Hey, I said, I'm trying!
Sandy: Well I don't think he's coming back anyway!
Sonic: Bucky, what are looking at?
Bucky: Sam!
Sonic: Guys, Cap's just fine.
Sam and SpongeBob walk toward Sonic and Bucky. Everyone sees Steve, now an old man, sitting on a log. The heroes go near him.
Bucky: Go ahead.
Sonic: Let's do this!
Bucky has a smile forming and looks over to Sam. He, Sonic, and SpongeBob walk toward the old man and instantly recognizes the now-elderly Steve Rogers.
Sam: Cap?
Steve: Hi, Sam. Hi, Sonic. Hi, SpongeBob.
Old Steve looks over to Sam and Sonic.
Sam: So did something go wrong, or did something go right?
Steve: Well, after we put the stones back, I thought... maybe... I'll try some of that life Tony was telling me to get.
Sam: How'd that work out for you?
Steve: It was beautiful.
Sam: I'm happy for you. Truly.
Steve: Thank you.
Sonic: You're welcome!
SpongeBob: At least you will be honored.
Sam: Only thing bumming me out is the fact I have to live in a world without Captain America.
Steve: Oh, That reminds me. (brings out his shield) Try it on.
Sam, SpongeBob, and Sonic look over to Bucky, who nods, and Sam holds Steve's shield.
Steve: How does it feel?
Sam: Like it's someone else's.
Sonic: At least Tails would be interested.
Steve: It isn't.
[Sam tries to hold back tears]
Sam: Thank you. I'll do my best.
SpongeBob: Congratulations, Captain Falcon!
Sonic: So proud of you, Sam!
Tails: (joins in) You'll do your best!
Steve: That's why it's yours. [shakes Sam's hand]
Sam: [seeing elderly Steve's wedding ring] You wanna tell me about her?
Steve: [smiling] No. No, I don't think I will.
Sonic: But maybe later.
SpongeBob: (smiles) MermaidMan and BarnacleBoy would be so proud.
1945
Steve has time traveled back to the 1940s to be with Peggy Carter. They are seen dancing to "It's Been a Long, Long Time" in their home, and they end with a kiss.
This is the end of the Infinity Saga for the MCU. Everybody in the movie theaters were so emotional of Steve Rogers becoming elderly. However, Peter Parker, a big Captain America fan, who would actually find out about his idol being an old man. Most importantly, Cap met the Red Skull for the first time since 1945 before the plane crashed and Steve got frozen in ice for 70 years until he thawed before meeting Nick Fury and formed the Avengers in 2012. The post-credits scene will show Silver's future in the later chapter.