Warning! This is a full spoiler alert!

The multi-verse of madness is truly one true madness. If you have seen What If? you'll now realize that the multi-verse is the What If? same multi-verse. Spoilers!

Doctor Strange started in a dream, Strange's dream. Or so he thought.

Villain. Not Wanda but The scarlet Witch. In order for her to revive her lost made up sons, she wants to travel to different universes to find a cure to a supposed future health issues her boys might have, and to make that into fruition she needs a special person, someone who could travel into different universes at will.

More spoilers!

As The Scarlet Witch tries to steal the power of America Chavez (the multi-verse traveler) Strange and Chavez ended up in a different universe of New York. To have an idea of this universe is, Strange knows where to go and who to ask. After some pleasantries, the good doctor realized that in this universe its not the Scarlet Witch who needs controling, its him.

Final spoiler!

The Illuminati. Introduces the council, we see that it's made up of Mr. Fantastic (John Krasinski), Black Bolt (Anson Mount), Karl Mordo (Chiwetel Ejiofor), Captain Carter (Hayley Atwell), and Captain Marvel (Lashana Lynch). It's an incredibly surprising scene, and Professor X's late arrival only adds to the spectacle -- especially because the theme song from the original "X-Men" animated series heralds his debut.

Scarlet Witch Killed Them All!