In 2021, a “WandaVision” fan theory that never came true captivated the minds of the Marvel Cinematic Universe fandom. As director Matt Shakman eventually revealed, Marvel’s very own devil expy Mephisto was never in “WandaVision,” despite rumors and speculation. However, “Agatha All Along” Season 1, Episode 3 — “Through Many Miles / Of Tricks and Trials,” puts the Mephisto issue back on the table by outright confirming that the character exists in the MCU. 

A discussion between Teen (Joe Locke) and Jennifer Kale (Sasheer Zamata) reveals strange snippets and uncomfortable allegations about Agatha Harkness’ (Kathryn Hahn) backstory. According to Jennifer, Agatha traded her own child for her considerable magic powers. The kid has been missing ever since, and may even have turned into an agent of Mephisto. Just like that, the door is wide open for one of the strongest Marvel villains who hasn’t yet appeared in the MCU … and that’s a big problem.

As Marvel’s best-known devil entity, Mephisto is the sort of antagonist who should loom far larger than any individual MCU movie or TV show. Unfortunately, the franchise is currently oversaturated with such folks. In 2023, Jonathan Majors’ tenure as Kang ended after he was found guilty in a high-profile domestic violence case. This left Phase 4 without its overarching main antagonist, who’s nevertheless still all over the Multiverse. It remains to be seen how the MCU intends to deal with the Kang situation. What’s more, two other massively powerful villains are on the way, with Ralph Ineson playing Galactus in “Fantastic Four” and Robert Downey Jr. set to portray Doctor Doom. As it stands, there are simply too many cooks in the villain kitchen … but what if Mephisto’s apparent arrival is specifically designed to tie into the MCU Doom’s story?

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It seems fair to assume that “Agatha All Along” intends to explore Mephisto further and possibly even show the villain in person. As “Loki” Season 1 proved with the first MCU Kang incarnation, He Who Remains, such a major debut on a Disney+ show is viable. However, shoehorning him in the villain-filled MCU right now will only make sense if they intend to connect Mephisto to the impending arrival of Robert Downey Jr.’s Victor Von Doom. 

In the comics, Doctor Doom and Mephisto are old adversaries. Doom seeks to free his dead mother Cynthia from the demon’s domain. What’s more, an early attempt at this directly leads to Doom’s infamous facial scars when a machine he uses to seek Cynthia breaks down. This doesn’t exactly endear Mephisto to him — and also causes him to hate Reed Richards, who had attempted in vain to help him with said machine. Confirming Mephisto at this stage suggests that the MCU intends to explore this aspect of Doom’s backstory, which could give the character a sympathetic quality many of the best MCU villains are known for. More importantly, it could be used to explain why Iron Man actor Downey is playing Doom. 

By combining the Mephisto aspects of Victor von Doom’s backstory with an alternate-timeline Tony Stark, the MCU would be able to bring in a complex and relatable major villain with very little legwork, which is precisely what it needs to switch Big Bad gears as swiftly as possible after the Majors situation. Tony is far and away the most prominent MCU character, and even an evil version of him would need barely any introduction. If a young Tony Stark was to lose a parent (and his good looks) to Mephisto, he might very well break bad and become both an armor-wearing technological wizard and a powerful actual wizard. Seeing as the comic book version of Doctor Doom has been known as Superior Iron Man and there are Sorcerer Supreme versions of him out there, this would be a twisty but ultimately surprisingly faithful interpretation of the character. 

There’s also another possible Mephisto-themed way to bring the Robert Downey Jr. version of Doctor Doom in the MCU, and it would mirror certain previous developments on the Sacred Timeline. Seeing as Jennifer introduces the concept of “agents of Mephisto” along with the demon himself, the MCU Doom could turn out to be such an agent — perhaps an alternate-timeline Tony Stark whom Mephisto resurrects after the events of “Avengers: Endgame” for his own purposes. If the show wants to go all out, it could even take a Tony with a radically different backstory and make him Agatha Harkness’ heavily-teased lost son. While the comic book Doom’s mother is also a witch, this might admittedly be harder to tie into the grander Doom lore … at least, unless Agatha’s stroll along the Witches’ Road is heading toward a hell-bound dead end.     

Since Downey won’t be in the MCU forever and Doctor Doom will almost certainly be revisited at some point down the line, this could even be used to tease the true Doctor Doom, peering into Mephisto’s hell with his machine and witnessing the Downey Doom before scarring his own face and starting his comics-accurate character arc somewhere in the Multiverse. Funnily enough, this approach would cast Downey in a similar fake-out villain role as Ben Kingsley, who plays the fraudulent Mandarin in “Iron Man 3” before the real one (Tony Leung) makes his grand entrance in “Shang-Chi and the Legend of the Ten Rings.” It would also reflect the comic book Doom’s infamous tendency to use fake copies of himself in various storylines. 

Of course, all of this is pure speculation until the MCU Mephisto actually makes an appearance, let alone ties into Doom’s backstory in some way. Still, the fact that the MCU has now announced both villains within just a few months does seem suspicious if you’re familiar with their history in the source material.