10 MCU Supervillains Who Could Realistically Appear in Avengers: Doomsday

Avengers: Doomsday is easily one of the most exciting upcoming projects in the Marvel Cinematic Universe. Set to open in theaters on December 18, 2025, the upcoming Avengers sequel is already looking to boast one of the biggest casts in the history of cinema. Fan-favorite characters from the MCU and Fox’s X-Men franchise are already confirmed for the film, with plenty of other surprises in store as well.

While the main focus of Doomsday will be the Avengers, Fantastic Four, and X-Men battling Robert Downey Jr.’s Doctor Doom, there is also room for some other major antagonists to appear in the film. Marvel has already dropped hints about several iconic villains showing up in the next Avengers movie. From Phase 1 villains to Avengers-level threats, these MCU antagonists stand a reasonable chance of appearing in Doomsday.

Kang the Conqueror Is the MCU’s Biggest Loose End

Jonathan Majors looking upset as Kang in Ant-Man and the Wasp: Quantumania.Credit: Image via Marvel Studios

Kang the Conqueror was originally intended to be the main antagonist of the Multiverse Saga, which would have culminated in his battle against Earth’s Mightiest Heroes in Avengers: The Kang Dynasty and Avengers: Secret Wars. However, Marvel Studios was forced to pivot away from this plan after firing actor Jonathan Majors. Robert Downey Jr. was brought in to play Doctor Doom, with The Kang Dynasty completely reworked as Avengers: Doomsday.

Despite Kang no longer being the main villain of the Multiverse Saga, there have been some indications that Jonathan Majors could return in Avengers: Doomsday. Kang the Conqueror and his variants, introduced in Loki and Ant-Man and the Wasp: Quantumania, are still out there somewhere, making up the most frustrating loose end in the MCU. Doomsday needs to revisit the Kang storyline, even if it is to bring the character and his variants to a swift and decisive end to make room for Doctor Doom.

Loki Is Already Confirmed to Appear in Avengers: Doomsday

Loki (Tom Hiddleston) sits on the throne at the end of the multiverse in the Season 2 finaleCredit: Image via Marvel Studios

Once the MCU’s greatest supervillain, Loki was the first person to go toe-to-toe with the fully assembled Avengers during the Battle of New York in 2012. Since then, however, Loki has undergone a surprising redemption arc, as depicted in his self-titled Disney+ series. At the end of Loki’s second season, the god of mischief finally achieved his “glorious purpose” by accepting the burden of upholding Yggdrasil, the new world tree at the center of the multiverse. In so doing, Loki became the “god of stories,” and one of the most powerful beings in the multiverse.

Although not technically a villain anymore, Loki is still one of the fiercest enemies the Avengers have ever faced. Tom Hiddleston is already set to reprise his iconic MCU role yet again in the upcoming Avengers film, where he is sure to play a pivotal role. As the centerpiece of the multiverse, Loki will most likely be one of Doctor Doom’s many targets in Doomsday, potentially putting the beloved character in danger of the one thing that has eluded him for decades–a permanent death.

Red Skull Is Still on the Loose After the Events of Infinity War

Red Skull at his post on Vormir in Infinity WarCredit: Image via Marvel Studios

The Red Skull was one of the first supervillains in the Marvel Cinematic Universe, leading the Hydra division of the Nazi army during World War II. After his battle with Captain America, however, the Hydra leader was teleported to another world by the Tesseract, which was later revealed to be the Space Stone. Red Skull spent decades guarding the Soul Stone on Vormir until the Mad Titan Thanos finally claimed the Infinity Stone during the events of Avengers: Infinity War.

Although Marvel Studios has made no indication that Red Skull will appear in Avengers: Doomsday, the villain is still lurking somewhere in the MCU. After Infinity War came out, the Russo Brothers hinted that Red Skull was now free to return to his old ways, now that the Soul Stone is no longer on Vormir. The Avengers could still have another run-in with the villainous super soldier, and Doomsday would be the best place for his potential return.

Ultron’s MCU Return Is Imminent

Ultron is holding up his fist in Avengers: Age of UltronCredit: Image via Marvel Studios

Ultron is perhaps the biggest missed opportunity in the entire MCU. An artificial intelligence unit so powerful that it could either save or destroy the world, Ultron is the only Avengers-level threat to only ever appear in one film. However, recent reports indicate that Ultron is returning to the MCU in the upcoming Vision Quest Disney+ series, which could factor into his potential appearance in Avengers: Doomsday as well.

If Ultron is indeed returning in Vision Quest, the series has an opportunity to explore an intriguing new story with the character: what if he actually fulfilled the role that Tony Stark originally envisioned for him? Vision Quest could show Ultron finally becoming the “suit of armor around the world” that he was always meant to be, which would make him the first line of defense against Doctor Doom when the supervillain finally arrives in the next Avengers movie.

Galactus Will Play a Major Role in the Future of the MCU

Ralph Ineson as Galactus in Fantastic Four First StepsCredit: Image via Marvel Studios

Galactus, the Devourer of Worlds, finally makes his MCU debut in The Fantastic Four: First Steps. While it is true that the cosmic being depicted in the film hails from the Earth-838 reality, Marvel Studios has confirmed that Galactus is an absolute being, existing in every alternate universe with no variants. This means that there is always a chance for Galactus to turn up in the Sacred Timeline–and Avengers: Doomsday could be the perfect project to facilitate his return.

Avengers: Doomsday is expected to reveal the truth about Franklin Richards, whom Doctor Doom is seen greeting in First Steps’ post-credits scene. Up until this point, Galactus was the only being who seemingly had any knowledge of Franklin’s true nature. It may be that the heroes are forced to turn to Galactus to discover the truth about the Richards boy and to help defend him from Doctor Doom.

The Beyonder Plays a Key Role in Secret Wars

The Beyonder flying through space in Marvel ComicsCredit: Image via Marvel Comics

The Beyonder is one comic character who has yet to make his debut in the MCU. An otherworldly being who exists outside the human concepts of space and time, the Beyonder is the one who initiates the events of the original 1984 Secret Wars event. He is also a crucial part of the 2015 crossover of the same name alongside the other Beyonders. It is their power that Doctor Doom steals at the beginning of this event, allowing him to transform into God Emperor Doom.

To properly adapt Secret Wars, the MCU will need to introduce the Beyonders into the narrative. Avengers: Doomsday needs to set up this plot point before Secret Wars, so that audiences fully understand the stakes once Doctor Doom steals the Beyonders’ power. As such, audiences should expect to see the Beyonder make his MCU debut at the end of next year.

Scarlet Witch Is Heavily Rumored to Return in Avengers: Doomsday

Elizabeth Olsen is the Scarlet Witch from Doctor Strange in the Multiverse of Madness.Credit: Image via Marvel Studios

Wanda Maximoff, a.k.a. the Scarlet Witch, has played both the hero and the villain during her tenure in the MCU. Originally introduced as a villainous henchman of Ultron, she eventually joined the Avengers to become their most powerful member. Unfortunately, she slipped back into her villainous ways during the events of Doctor Strange in the Multiverse of Madness, wherein she appeared to die in the collapse of the temple on Mount Wundagore.

Despite her apparent death, the Scarlet Witch deserves to return for the final installments of the Multiverse Saga. Fans have presented many theories that could explain her return, from her potentially surviving the temple implosion to a variant from another universe showing up to aid the Avengers. With Fox’s X-Men universe playing such a major role in Avengers: Doomsday, there is a possibility that the Earth-10005 variant of Wanda Maximoff could return. While Elizabeth Olsen has repeatedly claimed that she is done with playing this character, an MCU actor’s word can hardly be taken for fact at this point.

Namor the Sub-Mariner Is Returning to Fight Doctor Doom

Namor writing on his desk during Black Panther: Wakanda ForeverCredit: Image via Marvel Studios

Namor the Sub-Mariner, ruler of the underwater kingdom of Talokan, made a bold debut in Black Panther: Wakanda Forever. A mutant whose people have thrived thanks to Vibranium, Namor has a deep-seated hatred for the surface world. Despite failing to recruit Wakanda to join him in an alliance against the rest of the world, Namor still holds out hope that the Vibranium-rich nations will one day rule the globe.

Tenoch Huerta has been confirmed as part of the cast of Avengers: Doomsday, though how and why his character will join the rest of Earth’s heroes against Doctor Doom has yet to be seen. In the comics, Namor is often included in the Illuminati, a covert council of the world’s most influential heroes who make the difficult decisions that the Avengers could never. With the Illuminati heavily expected to appear in Doomsday, Namor could be included as a founding member.

Mephisto Is the MCU’s Newest Avengers-Level Threat

Sacha Baron Cohen in Ironheart as MephistoCredit: Image via Marvel Studios

After years of fan theories pointing to his introduction, Mephisto finally made his debut at the end of Ironheart. Sacha Baron Cohen plays the demonic dealmaker, who makes Riri Williams a sinister offer. After Ironheart, Mephisto’s MCU return is imminent, though it isn’t clear precisely where he might appear next.

Avengers: Doomsday is a big enough film to do justice to the magnitude of Mephisto’s character. Moreover, the ruler of Hell has a sinister connection to Doctor Doom. In the comics, it is revealed that Mephisto is in possession of Doom’s mother’s soul and emerges once a year to torment the villain and offer him a chance to win her back. While Doomsday may be too bloated already to include this story, it would be interesting to see the MCU acknowledge this connection.

Marvel May Have Already Revealed Thanos’s Return

Josh Brolin’s Thanos holding up the infinity gauntlet in Avengers: Infinity War.Credit: Image via Marvel Studios

Up until now, Thanos was the biggest villain in the MCU. The only person to single-handedly defeat the Avengers, the Mad Titan is still remembered for the massive threat he posed to the universe. It is Thanos that Doctor Doom must live up to when he finally arrives in the next Avengers film. Interestingly, Marvel may have already revealed exactly how Doom will step out from Thanos’s shadow.

In a recent exhibition put on by Marvel Studios in Shanghai, a lightshow revealed key details about Avengers: Doomsday, potentially including a cameo from Thanos himself. One scene features the mighty Doctor Doom ripping a skeleton out of an unseen enemy, perfectly replicating a key panel from Jonathan Hickman’s Secret Wars comic. In the 2015 event, Doctor Doom kills Thanos in this exact way, putting only a partial extent of his powers on display. It seems likely that this scene will take place in Avengers: Doomsday, bringing Doctor Doom face-to-face with Thanos for the first time in the MCU.