Why do Wanda Maximoff and our title hero seem to be zombies, and what is the Darkhold? Here’s a rundown and a viewing guide to help.It was already challenging enough to keep up with the 27 films and half-dozen Disney+ TV shows in the Marvel Cinematic Universe. But now, in “Doctor Strange in the Multiverse of Madness,” out Friday, you also have to keep track of multiple versions of Dr. Strange (Benedict Cumberbatch) and Wanda Maximoff (Elizabeth Olsen), also known as the Scarlet Witch. And who knows who else — it is the multiverse, after all, so there are multiple versions of, well, everyone.The trailers for “Multiverse of Madness” have made it out to be a crossover event that’s maybe not “Avengers: Endgame”-level, but certainly close. Eagle-eyed fans will have spotted connections to “WandaVision,” “Loki” and even zombie versions of a few characters, apparently from Episode 5 of the lesser-known Disney+ animated series “What If … ?,” as well as the M.C.U. debut of Patrick Stewart’s Professor X, the founder of the X-Men.It’s easy to feel overwhelmed with more than three days’ worth of M.C.U. content, and there is, of course, the bare minimum option of watching the first “Doctor Strange” film and calling it a day. But those who didn’t watch “WandaVision” may be left going “Westview what?” after the new movie.Here’s a guide to the five films and series you might want to brush up on before heading to the theater.‘Doctor Strange’ (2016)Tilda Swinton and Cumberbatch in the first film.Walt Disney Studios Motion PicturesDr. Strange’s solo film debut provides a primer on how Cumberbatch’s cocky neurosurgeon, Stephen Strange, came to be a master of the mystic arts, the Sorcerer Supreme and the guardian of the Time Stone. It also introduces his tempestuous relationship with Dr. Christine Palmer (Rachel McAdams), who returns in a big way in the fourth episode of “What If… ?” and also appears in a “Multiverse of Madness” trailer in a wedding gown (apparently marrying a man who is definitely not Dr. Strange, as the latter looks on from a pew). Also making a trailer appearance is Karl Mordo (Chiwetel Ejiofor), Strange’s onetime friend turned foe, as this film explains.‘Avengers: Infinity War’ (2018)Benedict Wong, left, Cumberbatch, Mark Ruffalo and Robert Downey Jr. teamed up in “Avengers: Infinity War.”Marvel/DisneyIn Dr. Strange’s “Avengers” debut, he is kidnapped by Ebony Maw, who is after the Time Stone. Tony Stark and Peter Parker eventually rescue him, and it becomes evident how much more powerful he has become since “Doctor Strange,” as he holds his own against Thanos, the Eternal-Deviant warlord, despite possessing only a single Infinity Stone compared with Thanos’s four. Strange also breaks the rules and looks forward in time to see all the possible scenarios in which the Avengers win.The film plays an important role in establishing Wanda’s back story, as its events are the source of her grief in “WandaVision,” and continue to haunt her in “Multiverse of Madness.” In the earlier movie, Wanda was forced to kill Vision, with whom she was romantically involved, to prevent Thanos from stealing the Mind Stone from Vision’s head, only to watch Thanos reverse time, pluck it out and kill Vision again.‘WandaVision’ (2021)Elizabeth Olsen as Wanda Maximoff in the series.Marvel Studios/Disney+This retro-aesthetic Disney+ show is hardly peripheral; the nine-episode series, which pays homage to 1950s sitcoms like “The Dick Van Dyke Show,” supplies crucial plot details that set up the events of “Multiverse of Madness.” Wanda is essentially a co-lead of the new film, and this series illustrates how her grief over Vision’s death leads her to torment the small New Jersey town of Westview.When we last saw Wanda, in the finale’s post-credits scene, she’d just lost the versions of Vision and her twin sons she’d magically created, which led her to embrace her identity as the Scarlet Witch and begin exploring the Darkhold, a book of spells that could allow her to reunite with her now-nonexistent family.In “Multiverse of Madness,” a distraught Wanda is still struggling to process the original Vision’s death in “Avengers: Infinity War,” as well as her attempt to escape it in the fantasy she created in “WandaVision.” In one of the trailers, she is greeted by her sons in their Westview home, though Wanda’s voice-over identifies the apparently joyful reunion only as a recurring dream.‘What If … ?’ (2021)Strange variants in the animated “What If …?”Marvel Studios/Disney+This nine-episode animated anthology series, which tells the stories of alternate versions of M.C.U. heroes in multiple realities, debuted with little fanfare in August, but Episode 4 provides some important context for “Multiverse of Madness.” Titled “What If … Doctor Strange Lost His Heart Instead of His Hands?,” it introduces a variant of Dr. Strange, Strange Supreme, created after Strange lost his girlfriend, Christine, in a car crash and became consumed by dark magic. After she vanishes in his arms, the evil Dr. Strange rips apart reality and is left alone to nurse his broken heart.While it initially seemed, from his trailer appearance, as though the Strange Supreme variant would be a main antagonist of “Multiverse of Madness,” Cumberbatch said in a recent interview that the character was not, in fact, Strange Supreme but an even more menacing version: Sinister Strange.Still there are other “What If … ?” variants who seem to appear in “Multiverse of Madness,” including a live-action version of Captain Carter (voiced by Hayley Atwell in “What If … ?”), a Peggy Carter variant who received the super-soldier serum instead of Steve Rogers and appeared in a trailer fighting a variant of the Scarlet Witch. Also returning: the terrifying Zombie Wanda and Zombie Dr. Strange from Episode 5 (“What If … Zombies?!”), which probably explains why “Multiverse of Madness” is being billed as the M.C.U.’s first horror film. Episodes 8 and 9 also show Ultron discovering multiple realities and seeking to conquer them.‘Spider-Man: No Way Home’ (2021)Tom Holland as Peter Parker, opposite Cumberbatch in “Spider-Man: No Way Home.”Matt Kennedy/Sony PicturesThe director of “Multiverse of Madness,” Sam Raimi, has said that the new film is a direct continuation of the last Marvel Studios blockbuster, “Spider-Man: No Way Home,” released in December. When we last saw Dr. Strange, he’d just caused everyone to forget the existence of Peter Parker to stop the multiverse from exploding. This was necessary because of a botched spell Dr. Strange had cast that was designed to make everyone forget Peter was Spider-Man, which only ended up pulling Spider-Men and villains from alternate M.C.U. universes into the same one. At the end of “Spider-Man: No Way Home,” the spell appears to have worked, but it remains to be seen if or how the consequences of Dr. Strange’s actions will play into “Multiverse of Madness.”Bonus: ‘Loki’ (2021)Owen Wilson as Mobius M. Mobius and Tom Hiddleston as Loki in the series. Marvel/Disney+Will we see the hopelessly bureaucratic Time Variance Authority, an organization that polices time travel to prevent branching timelines, show up to bust some time travelers in “Multiverse of Madness”? The stand-alone “Loki” series, which takes place in an alternate M.C.U. timeline, also explains the idea of variants from different timelines (among them: Richard E. Grant’s Classic Loki and Alligator Loki). More