The Marvel Cinematic Universe first teased the larger multiverse in 2019's Spider-Man: Far From Home when Mysterio used the story that he was from another universe and even gave the Earth-616 designation that will be familiar to comic fans. Mysterio's story was a lie, but the multiverse was seemingly confirmed by the upcoming Doctor Strange in the Multiverse of Madness.
There are a number of interesting alternate realities that could now make an appearance in the MCU, including the terrifying Marvel Zombies reality that will be explored by the animated What If...? series coming to Disney+ in 2021. Of course, that isn't the only horrifying alternate universe that the MCU should explore as there a few other frightening options fans might see one day.
10 Earth-51412: Edge Of Spider-Verse
Early rumors for the upcoming third MCU Spider-Man film are also revealing a multiversal twist, and as fans have seen with Spider-Man: Into The Spider-Verse, there are quite a few alternate Spider-Men out there. The Edge of Spider-Verse comic series explored a few of these worlds, with one dark reimagining of Spider-Man's origins sure to terrify movie fans.
Patton Parnel lived a dark, abused version of Peter Parker's life, and after he was bitten he began to transform into a cannibalistic creature that devoured his Uncle Ted and poisoned his neighbor Sarah Jane before he was killed by Morlun and the Inheritors.
9 Earth-11080: Marvel Universe Vs. The Punisher
2010's Marvel Universe vs. The Punisher featured a world overrun by a cannibalistic virus that infected the most powerful heroes and villains of the Marvel universe, though Frank Castle had become immunity due to receiving a super dose of the chemical that infected the world.
The infected superhumans devolved into predators that carved up the world into individual tribes as the Punisher set about correcting his mistake. Spider-Man, Wolverine, Hulk and the Avengers all factored into the series and connected spin-offs that further explored the fall of the Marvel Universe.
8 Earth-11326: Age Of X
While the X-Men or mutants have yet to be officially introduced into the MCU after the return of the film rights to Marvel Studios, the team's debut is inevitable, and the alternate reality Age of X storyline would offer a dark take on both Marvel's mutants and the MCU heroes.
Age of X features the last mutant survivors as they fought a daily war to secure their borders against the never-ending threat of humanity and their Avengers, though it was all revealed to have been a shift in reality due to the powerful mutant Legion, which could help explain the X-Men's emergence in the MCU.
7 Earth-3931: Vampire Avengers
The Exiles were a team of multiversal X-Men that were gathered together to help repair damaged universes, which brought them to Earth-3931, which featured a team of Avengers that had been transformed into vampires.
While Captain America's battle with Baron Blood in the mainstream Marvel universe ended with Blood's death, the alternate world saw Captain America transformed into a vampire, with the rest of the Avengers falling soon after. The rest of the world would have fallen victim as well if the Exiles hadn't intervened and taken out the head vampire.
6 Earth-12101: Deadpool Kills The Marvel Universe
While Deadpool hasn't officially joined the MCU yet, a third film starring the Merc-with-a-Mouth has been announced by Marvel Studios which opens the possibility to another terrifying reality in the multiverse that first appeared in Deadpool Kills the Marvel Universe.
After that reality's Deadpool underwent a failed brainwashing that drove him to a new level of insane, he dedicated himself to killing every hero and villain on the planet before he spread his evil to the multiverse as the fourth-wall murdering villain known as Dreadpool.
5 Earth-666: Avengers Of The Undead
When Captain Britain was working with Hawkeye's team of Secret Avengers, he was tasked with hiding the powerful Orb of Necromancy that he kept in the dark reality of Earth-666, which was overrun with supernatural creatures like vampires and werewolves.
The world was divided by the various factions of the supernatural, though the dark heroes of that world had formed together as the Avengers of the Undead which was led by Brother Voodoo and featured monsterized members like a lycanthropic Captain America and a fully transformed Man-Spider that had no love for the living.
4 Earth-42777: Emperor Stark
The Exiles weren't the only team traveling across the multiverse fixing broken universes, as another group known as Weapon X also explored dark realities, including a world run by a Doctor Doom-scarred Emperor Stark.
In this dark reality, Iron Man had managed to take control of the planet by manipulating it through a number of devastating wars, leading to the death of many of the world's heroes. All that remained was a small group of rebel Inhumans led by the widowed Susan Storm, with the Exiles again interfering to change the balance of power in the reality.
3 Earth-TRN666: Thanos Wins
While the heroes of the MCU already received a taste of a reality in which Thanos achieved his ultimate goals by erasing half of the population of the universe in Avengers: Infinity War, there exists a still darker universe where "Thanos Wins."
Determined to finally impress Death, Thanos eradicated every living being on planet Earth including the superheroes and Frank Castle. The former Punisher made deals with both Mephisto and Galactus to find a new life of vengeance as the Cosmic Ghost Rider and stop King Thanos' dark reality from ever happening.
2 Earth-10011: The Cancerverse
After a devastating battle in space during the War of Kings event created a rift into another universe known as the Fault, the 616 reality fell prey to the threat of the Cancerverse, which was a parallel reality where Captain Mar-Vell's death led to deal with the Lovecraftian Many-Angled Ones.
The Eldritch horrors soon took over the superhero population who became corrupted servants in a world without death led to a tainted never-ending life that almost bled into the mainstream Marvel universe before it was sealed off due to the sacrifice of Star-Lord, Drax, Nova and Thanos.
1 Earth-9591: Ruins
While Marvels showcased the best and brightest that Earth-616 had to offer, Ruins took a dark and twisted look at an alternate Marvel world where everything that could have gone wrong, did so in the worst possible way. The various scientific accidents and experiments that created Marvel's heroes went extremely wrong in the Ruins reality.
The Fantastic Four died on their test run in space, Bruce Banner was transformed into a living mass of tumors instead of the Hulk, and Peter Parker's spider bite left him with a terrifyingly infectious disease that ultimately killed the narrator in the truly darkest Marvel timeline.