The following contains spoilers for Doctor Strange in the Multiverse of Madness, now in theaters.
In Doctor Strange in the Multiverse of Madness, the Marvel Cinematic Universe's mainstream Earth -- Earth-616 -- once more came under threat. Just like Spider-Man: No Way Home had multiversal visitors, America Chavez intruded, with Strange shockingly discovering demons weren't chasing her; it was his world's Scarlet Witch. The grief-laden Wanda Maximoff wanted to harness America's Multiverse-hopping abilities to find a home to be with her sons, which created a brutal supernatural war filled with horror and gory deaths. Thankfully, Team Strange won and crafted a hopeful future, but threads were set up for a sequel that could paint a dark picture of despair.
Doctor Strange 3 Could Focus on Stephen and Clea
Charlize Theron showed up as Clea in Multiverse of Madness' mid-credits scene, ripping a hole through space and time to escort Strange on a journey. She said the Multiverse was still fraying and seemed to jump into a Dark Dimension akin to where Dormammu was stuck. Thus, it seems like they headed out on an adventure to patch rifts after the events of Loki, Strange's memory-wiping spell in No Way Home, and this film's world-jumping shenanigans.
This could lead to a Stephen and Clea romance, per the comics, possibly shaping her to become a Sorcerer Supreme someday. However, just like Wanda wasn't to be trusted, this Clea could be an evil variant wanting to harness Strange's power and the corruption inside him after he used the Darkhold to fight Wanda. Stephen's quite mentally vulnerable right now and could easily be turned into a villain, like how the book manipulated Wanda. But if this Clea's not good, chances are he'll find one who is and can possibly heal him.
Doctor Strange 3 Can Bring Baron Mordo Back Into Play
Mordo vowed to kill Strange and the Kamar-Taj sorcerers after the first film, hating how they used the Time Stone. Seeing as Strange also messed with reality in No Way Home and now was a part of Multiverse of Madness' world-hopping mess, Mordo could view it as the final straw. He wouldn't even have faith in Kamar-Taj given how Sorcerer Supreme Wong and the others failed, wanting to target them for being failures and liabilities as well.
It's easy to see Mordo wanting America out of the picture too, knowing her power could invite new villains over or send corrupted tyrants to invade other realms. What's interesting is seeing as Strange left Mordo-838 on his world angry and bitter, especially after his Illuminati peers died there, he -- and maybe other Mordos -- could become a council, akin to Rick and Morty, to try to solve the Strange problem permanently.
Doctor Strange 3 Can Expand Marvel's Magical Roster
Wanda finally realized she was a monster and brought her ritualistic base down on Mount Wundagore. She killed herself and destroyed all Darkholds across the Multiverse, but all these worlds would still have similar hubs of dark magic lingering. As such, variants of Kaecilius and his cult could arise to harness it and free Dormammu, or new enemies such as Nightmare could arrive. Given how dreams are snapshots into variants' lives, the latter could easily track and feed off of heroes.
Mephisto is another option, realizing America can help him visit realms to feed off wishes and claim souls. Doctor Doom could also arise, given Earth-838 had a Reed Richards, to seek dark magic on Earth-616. Then there's Agatha Harkness, who can return outside her planned spinoff if Wanda's binding spell was broken after her demise. Conversely, heroes such as Brother Voodoo or even Blade could help out, realizing mystical trouble's bleeding over. With America also learning under Wong, she may evolve into a prodigy and possibly be next in line as Sorcerer Supreme. She can rally other magical heroes like Hellstrom or Magik to help out as well, with Wong realizing he needs dedicated Mystical Avengers.
See how a sequel has been set up for Doctor Strange in the Multiverse of Madness, now in theaters.