Even though they made the film instantly iconic, the villains of Spider-Man: No Way Home originally had a much smaller role in Spidey's third MCU outing. According to The Wrap, the returning villains from previous Spider-Man films, including Alfred Molina's Doctor Octopus and Willem Dafoe's Green Goblin, were initially planned to only appear in a post-credit scene. However, a suggestion from Marvel Studios president Kevin Feige changed the plot of Jon Watt's third Spider-Man film.
According to co-writer Chris McKenna, the only major story ideas that came up when planning the film at first were picking up after the events of 2019's Spider-Man: Far From Home and having Doctor Strange (played by Benedict Cumberbatch) appear in the film. "And then, I don't know if it was Kevin [Feige's] idea," said McKenna, "The idea of doing something with the other villains and teasing that at the very end [of the movie], I think in [an end-credits scene] was floated."
McKenna and co-writer Erik Sommers then came up with different stories that would lead to a post-credit scene with villains from Sam Raimi and Marc Webb's Spider-Man films being introduced through the multiverse, now a pivotal part of the MCU. As the two were coming up with potential plots, McKenna said, "I think it was Kevin who goes, 'Remember that idea with all the villains that we were talking about for a tag? That Sinister Six idea? Why don't we just do it in the movie? Make this movie about that?' and then that just sort of blew everything open."
The writers already planning to use Doctor Strange in the film helped with bringing in characters from the multiverse. "We were already talking about the idea of It's a Wonderful Life with Peter going to Doctor Strange and trying to reverse the fallout from everything," McKenna noted, "So it was already in the air that he was going to Doctor Strange to help clean up this giant existential mess that had happened to him, so then it all started coming together,."
Spider-Man: No Way Home, also starring Tom Holland, Zendaya, Jacob Batalon, and Marisa Tomei, is playing in theaters now.