Marvel Studios' What If...? introduced audiences to the various realities across the Multiverse that exist outside of the traditional Marvel Cinematic Universe. With the concept explored in plenty of other projects including Spider-Man: No Way Home and Loki, there's no surprise that in Doctor Strange In The Multiverse Of Madness there appears to be plenty of connections to the animated Disney+ show.
Indeed, while those other projects have also entered into the Multiverse it's What If...? that shows the full range of what could be unleashed if the barriers between realities begin to break. The trailer for Doctor Strange 2 has hinted at some pre-existing links between the two projects but there are plenty of other ways that their narratives may intertwine.
The Watcher
It would be incredibly surprising for Marvel to explore the Multiverse further and ignore the presence of Uatu the Watcher. He almost broke his vow of non-involvement in What If...? and with the Multiverse on the brink of collapse, perhaps Uatu will finally follow his comic book roots and break ranks completely.
Fans have already seen the Watchers in live-action in Guardians Of The Galaxy: Vol. 2 but Uatu is the most significant amongst them. He may be able to offer some advice to Stephen Strange as he navigates between worlds, considering he has been observing all of existence for most of eternity.
The Realm Between Realities
Fans were briefly given a look at the realm between worlds in What If...? where Utatu did most of his watching. The setting allowed for the iconic image of Ultron breaking through, out of its own reality and into this strange and mysterious dimension.
The trailer for Doctor Strange In The Multiverse Of Madness appears to show the cracking mirror-like shards that represent this realm between worlds in the animated series. The power of the Scarlet Witch may be enough to impossibly invade this space, much like the Stark-created android.
Ultron
The trailer for the blockbuster has indicated that there may be a link to Ultron in the creation of the Iron Man Sentry droids that the Illuminati seem to be employing. What If...? audiences will know that their very existence could lead to disaster.
In the series Ultron was able to break out of its own reality, infecting androids across the Multiverse and allowing its army to travel between worlds. With the Infinity Stones briefly in its grasp, it was unstoppable. As Strange falls through reality it may give Ultron the opportunity to expand once again. There's a possibility that the Zola variation of these robots may take advantage though.
Strange Supreme
Strange Supreme is one of the most powerful entities within the Multiverse and seemingly the strongest Variant of the Sorcerer Supreme. Consuming plenty of dark magic, the character was driven to the edge of sanity after the loss of his beloved. Avoiding the death of Christine Palmer became his obsession.
In doing so, he destroyed his whole universe, although Supreme Strange would defend the Multiverse when called upon. The trailers for Doctor Strange 2 have already revealed that this Variant will make an appearance, bringing the live-action movie closer to the animated Disney+ project.
Captain Carter
Captain Carter may just be a more valiant version of Captain America, with this reality seeing Peggy gain the Super Soldier Serum and turn the tide of war. The poster of Doctor Strange In The Multiverse Of Madness teased the shield of the hero and there's some speculation she could be a member of the Illuminati.
The character is heroic and defiant in the face of injustice. Alongside Steve Rogers, in the Hydra-Buster armor, Captain Carter has followed a similar path to the original Captain America but is very much aware of the Multiverse. She may be a useful ally to Strange, especially now that his reality is without a Peggy of its own.
The Guardians Of The Multiverse
The Guardians Of The Multiverse were a team put together by Uatu to try and save the Multiverse from Ultron and its forces. They were specially picked to create a timeline of events that would result in victory, even at the potential cost of a betrayal from Killmonger.
Characters like T'Challa's Star-Lord or Captain Carter were involved in the team, and the notion of this superhero unit could bleed into Multiverse Of Madness. Of course, the Illuminati may replace such a role, but it's possible that these Guardians were the predecessor to the cabal.
Zombie Reality
Marvel's Zombies is a hugely popular narrative from the comics and has become a major factor of the What If...? series. Fans have seen a whole reality taken over by Zombies, with some of the most recognizable heroes and villains decaying and becoming these brain-eating beasts.
The trailer for Doctor Strange 2 has indicated that there will be some kind of Zombie invasion, or Strange may visit the undead reality seen within the show. Strange and Wanda are just two characters infected with the disease within the footage already seen, so a re-watch of the episode is key to see what other vigilantes may turn up as decomposing versions of themselves.
An Animated Setting
The stories of Marvel's What If...? take place in an animated setting. The idea behind this was that animation could allow Disney to achieve various narratives that would be far too expensive to try to adapt in live-action. But the trailer for Doctor Strange In The Multiverse Of Madness could play around with the idea.
It appears that one shot in the trailer indicates that America Chavez and the Sorcerer Supreme have fallen from an animated world. It's not a new idea in the context of comics to see the visual style change between the Multiverse, but it would be an intriguing concept to see on screen.
Multiversal Monsters
Shuma-Gorath or Gargantos as the creature will come to be known, is one of the many mystical monsters from the Marvel Universe. Fans of the animated series on the Disney+ streaming service will have seen the beast fight against Captain Carter and imbue Strange Supreme with some of its power.
But the trailer for Multiverse Of Madness teases the return of the monster and its debut in live-action. It appears the Doctor Strange MCU audiences are familiar with will be taking on this Multiversal threat, as its tentacles cause havoc on the streets of New York.
Location Cameos
Ultron's fight with Uatu saw the duo battle throughout a multitude of different realities. The idea of falling through worlds will surely come into play in the Doctor Strange sequel and thus there may be some settings that were previously displayed in an animated form.
Interestingly, one of the worlds that the pair briefly entered was Mustafar from the Star Wars galaxy. The trailer for Multiverse Of Madness teases a few other settings, some of which were not seen in What If...? including the comic book backdrop of the Dinosaur-filled Savage Land.