[30][31] In an unrealized scene in the film Avengers: Infinity War (2018), Strange sends Thanos through a series of alternate universes, emulating the Magical Mystery Tour.

[42] In Endgame, the Avengers travel through the Quantum Realm to 1970 Camp Lehigh, 2012 New York, 2013 Asgard, and 2014 Morag and Vormir, to retrieve the six Infinity Stones displaced through time.

[43] The film establishes the rules of time travel in the MCU, rejecting the grandfather paradox and the butterfly effect which state that changes to the past will affect the future in the same timeline.

[46][47] Afterward, Steve Rogers / Captain America returns the Infinity Stones and Mjölnir to their original timelines, choosing to stay behind with an alternate version of Peggy Carter in 1949 and grow old with her.

[80] The Sacred Timeline is depicted as a circular shape when viewed from the Citadel at the End of Time, a concept conceived by the series' storyboard artists and thought by director Kate Herron to be a "striking image".

[85] The alternate realities featured in the season include one where Carter becomes the super-soldier Captain Carter,[86] one where T'Challa becomes Star-Lord,[87] one where the Avengers are assassinated by Hank Pym / Yellowjacket during the events of the tie-in comic Fury's Big Week (2012),[88] one where Stephen Strange is corrupted by dark magic,[89] one where Janet van Dyne / Wasp triggers a zombie apocalypse,[90] one where Erik "Killmonger" Stevens rescues Stark before causing a war between Wakanda and the U.S.,[91] one where Thor was an only child and lives a party lifestyle,[92] and one where Ultron uses the Infinity Stones to exterminate all life in the universe.

[104] In the film, Parker refuses to send Octavius, Osborn, Marko, Dillon, and Connors to their deadly fates in their original realities, trapping Strange in the Mirror Dimension.

[107] Screenwriters Chris McKenna and Erik Sommers began exploring the idea of the multiverse and potentially revisiting characters from past Spider-Man films early on during the writing process, initially planning for this to be a minor tease for fans.

The company refers to the sequence as the "America Portal Ride", with head animator Alexis Wajsbrot seeking to "echo the craziness" of Doctor Strange's Magical Mystery Tour.

After several futile attempts to stop the Loom from overloading, Loki uses his burgeoning time-slipping ability to return to the Citadel at the End of Time, where He Who Remains resided in season 1.

After much consideration, Loki sacrifices himself by using his powers to destroy the Loom, revive the dying timeline strands, and reform them into a tree-like structure, seating himself at its center in the Citadel ruins to manage the tree in perpetuity.

[174] The sixth episode introduces an original MCU character named Kahhori, a young Mohawk woman in an alternate timeline who seeks to discover her new-found powers after the Tesseract crash-lands in the Haudenosaunee Confederacy in pre-colonial America where European colonization has not occurred.

[180] Feige has described that Wilson will discover the Sacred Timeline in the film and find it fascinating, but he will realize that Paradox's plans may not be what they seem and he will learn that his offer isn't as simple and there are "universe sized" stakes on the way.

[185] Keen and Stanford confirmed their roles to not be variants of Laura and Pyro respectively but the same ones they portrayed in the X-Men film series, with the backstory provided by Reynolds and director Shawn Levy being that they were pruned by the TVA some years after their last appearances instead of being taken from specific points of certain timelines.

[186][187] Wolverine comes from a reality where all his fellow X-Men died, while the rest of those characters appear as inhabitants of the Void, with Pyro and Sabretooth working for Cassandra Nova (Emma Corrin), while Laura, Elektra, Blade, the Human Torch, and Gambit oppose her as resistance members which previously included Daredevil, Magneto, the Punisher, and Quicksilver.

Other characters who work for Cassandra are the Juggernaut (Aaron W. Reed), Blob (Mike Waters), Azazel (Eduardo Gago Muñoz), Callisto (Chloe Kibble), Lady Deathstrike (Jade Lye), Psylocke (Ayesha Hussain), Arclight (Jessica Walker), and Toad (Daniel Medina Ramos), all portrayed by stunt performers over their original X-Men film series actors,[188][189] as well as the Russian (Billy Clements) and Bullseye (Curtis Rowland Small).

[198] Marvel Studios executive Nate Moore previously referred to the main MCU universe as Earth-616 in November 2021,[199] and Feige also began using the term internally prior to the release of Multiverse of Madness.

[67] During the Avengers' Time Heist in Endgame, Natasha Romanoff / Black Widow, Clint Barton / Hawkeye, James Rhodes / War Machine, and Nebula time-travel to an alternate Morag in 2014.

[95] The animators used an artistic effect called the Kirby Krackle in these two episodes to demonstrate the multiversal power of Ultron and the Watcher, which Bradley was adamant on including due to it never having been used before in the MCU.

[186] The Magical Mystery Tour sequence in Doctor Strange was praised by critics, with Umberto Gonzales of TheWrap calling it a "trippy psychedelic thrill ride" and Britt Hayes of ScreenCrush describing it as "astounding, elaborate stuff".

[100] Lee and DeFore also noted the level of fan service present in the film, which was echoed by Bilge Ebiri of Vulture and Don Kaye of Den of Geek.

[121] TheWrap reviewer Alonso Duralde felt that Multiverse of Madness failed to achieve Everything Everywhere All at Once's level of "wit and nerve and character", but commended the America Portal Ride scene as "memorably trippy".

[237] Collider's Ross Bonaime, and The Atlantic's David Sims, and The Mary Sue's Princess Weekes all criticized the film's excessive reliance on fan service.

Matt Purslow of IGN was disappointed that viewers' speculation did not pay off, calling this an "unfair trick from Marvel",[250] while his colleague Carlos Morales criticized the casting as unnecessary and hollow.

[269] Belen Edwards of Mashable argued the opposite, believing that the Illuminati's quick and brutal death sequences were a "nice change of pace" from No Way Home's level of fan service.

[303][304] Eliana Dockterman of Time described the scene as fulfilling Sony's "corporate mandate" of connecting the SSU to the MCU, pointing out how it contradicted many plot elements of Homecoming and No Way Home.

[306] Co-director Kemp Powers later stated that the No Way Home reference was meant to be a meta gag and throwaway line that screenwriters Phil Lord and Christopher Miller came up with to add humor to their films, confirming that it has no connections to the MCU.

[306] X-Men '97 (2024), the Disney+ revival of X-Men: The Animated Series (1992–1997), was produced by Marvel Studios Animation, but it's set in a separate continuity from the MCU's Sacred Timeline, though Winderbaum suggested that the show's characters can appear eventually in MCU projects thanks to the potential for connections from Loki and every other multiverse stories,[309] saying that "if your brain wants to go there, you know there's always the potential for connections" while acknowledging that the show takes place in a universe of different 1990s cartoons.

[311] However, former head writer Beau DeMayo stated on Twitter that he and the showrunners saw the show set in its "own branching tree" over the MCU's, but concluded it would depend on Marvel whether to make connections and admitted "a few leaves" may mingle with another at some point.

[322] At the D23 Expo in September 2022, a new multiverse-focused attraction at Disney California Adventure was revealed to be in development,[323] featuring numerous MCU heroes from multiple universes on a quest to defeat "King Thanos".