WARNING: The following contains major spoilers for "The Vat of Acid Episode," Episode 8 of Rick and Morty Season 4.
One major concern fans held with Avengers: Endgame was how time-travel was used so conveniently in the script with no hard and fast rules set. Issues such as Captain America living in the past and growing old and all the ripple effects and branched worlds that should have been created as Earth's Mightiest Heroes messed with the timeline, were all clear points of contention.
So much so that when attempting to explain the time travel, the Russo brothers and the film's writers, Stephen McFeely and Christopher Markus, often came off like they were on different pages. Now, Season 4 of Rick and Morty takes shots at the film with Rick making it clear time-travel is just being used as a cop-out in pop culture these days.
Morty challenges Rick's intellect so the mad scientist uses time crystals and one of the kid's ideas to creates a "do-over" remote. It allows Morty to save life at a point in time like a game and if things don't go his way, he can just jump back to the saved moment. To Morty, it's time-travel done right and he goes all out as he makes bad decisions followed by good ones, knowing he has the safety net to reset.
He eventually falls in love with a young girl and after a traumatic ordeal where they crash in the snow on vacation, Morty almost resets their time to when he first sees her at a cafe. Nonetheless, they survive and eventually all seems well as they meet each other's families and whatnot. That is until Morty's dad, Jerry, accidentally presses the reset button thinking it's his TV remote. This pushes Morty back in time before he met the girl and send him insane. A series of unfortunate events play out and Morty loses the reset point, with it now becoming a point in time when the girl thinks Morty's a creep.
Heartbroken, he has an existential crisis but learns to live with his fate and he goes to Rick to give the remote back. But the twisted Rick reveals he wanted to teach Morty a lesson about how much of a god he can be. He confesses this wasn't time-travel, which he thinks is stupid after seeing the likes of Ant-Man and the Wasp doing it -- it's a transdimensional teleporter. Rick admits quantum leaping leaves plot holes because no film wants to address the butterfly effects and it's why he doesn't respect temporal stories, especially if Avengers can pull it off. Instead, Rick's remote creates branched off realities every time Morty presses the reset button, and he's shunted into another reality to move forward.
Rick fixes the multiverse by rigging the remote to create space and kill all the other Morty's existing so that only the prime Morty moves on. The boy's horrified to hear this as Rick shows him the others dying when he uses the remote for selfish gain and replaces them. Rick compares it to The Prestige with the dead Morty's all being reality clones. Morty is sickened but Rick tells him he's designed it so he can take Morty back to the first moment he gave him the remote. However, it comes at a price as all his sins will be reconciled in their original reality but hey, at least "the greedy little junkie" wouldn't have killed the other Morty's.
After Morty agrees, everyone from the FBI, the #MeToo movement to the AARP show up to arrest him for all the stuff he did thinking he wouldn't get caught. But after saving him, Rick admits this isn't even their reality because he couldn't risk Morty ruining the original Rick and Morty homeworld. They use the same vat of acid Morty ridiculed at the start of the episode to fake his death and this allows Rick to take Morty home. However, he reminds Morty how genius he is and the audience that these popcorn movies don't take logic, consequences or science seriously.
Created by Dan Harmon and Justin Roiland, the second half of Rick and Morty Season 4 airs Sundays on Adult Swim. Seasons 1 through 3 are available to stream on Hulu.