Warning: MAJOR SPOILERS for Spider-Man: Far From Home ahead.
Spider-Man: Far From Home filmmakers explain why Mysterio (Jake Gyllenhaal) was chosen as the main villain. The final movie in the Marvel Cinematic Universe's Phase 3, directed by Jon Watts, Far From Home tackles the aftermath of Avengers: Endgame. Putting the focus on Peter Parker (Tom Holland) as he grapples with the death of his mentor Tony Stark/Iron Man (Robert Downey Jr.), the young hero finds himself across the pond for a much-needed recreational trip.
Sadly, what was supposed to be a vacation got turned upside-down when Nick Fury (Samuel L. Jackson) recruited him for a new mission that teamed him up with Quentin Beck/Mysterio - a hero who allegedly came from another dimension after Thanos' snap in Avengers: Infinity War opened a portal. Beck sold his story effectively to both Fury and Peter, but as comic book readers know, chances were that it was nothing but a ruse. Lo and behold, in arguably one of the most creative exposition scenes in the MCU, Mysterio revealed that he, alongside several disgruntled Stark Industries employees, planned everything so they could get hold of a piece of powerful Stark technology known as E.D.I.T.H. (Even Dead I'm The Hero).
It was a well-executed plot twist that remained true to Mysterio's character in the comics, and Feige says that this particular element of the villain was what initially convinced them to use him in Far From Home. During an interview with Screen Rant for the film, the MCU architect explains this in detail, adding that the potential dynamic between Beck and Peter was also a factor in the decision making.
Getting into spoiler territory, so you’ll be careful how you use this. How exciting for us to actually do Mysterio. The fishbowl illusionist who everybody rolls their eyes out in the comics; the green smoke trails, we were like, “We gotta do that. We gotta swirl them around.” Which we really wanted to do, and showcase his illusion powers in a way that it kind of was in the comics always too: science-based, not necessarily magic...
And also [we used the father-son dynamic] to make the turn not just an obvious “Well, of course he’s going to be bad, he’s bad in the comics,” but also to make it more of a heartbreak. Because even though you know on some level it must be coming, you like that relationship so much that it hurts you when it happens.
As for Watts, the filmmaker cites the possibility of executing crazy visual spectacles as what lured him to use Mysterio in Far From Home. He reveals that they used the comics for reference when it comes to staging Beck's over-the-top theatrics - something that readers will surely appreciate.
Oh, yeah. There’s so many frames that are almost direct pulls from Mysterio comics. I think that’s the first time I sat there and felt like I was living in a comic book that I had read.
That’s the reason why you have Mysterio as your villain. It’s the excuse to do that kind of crazy visual sequence.
Using Mysterio for Spider-Man: Far From Home was also a great move due to the fact that fans haven't seen this villain on the big screen before. His deceptive tactics worked well since Peter was at an emotionally unstable place in having to deal with the death of Stark, making him more susceptible to the villain's ministrations. But none of this would've worked without Gyllenhaal's stellar performance in the role. Fans assumed there would be a twist involving his character, but he was still able to sell his fake story for the better part of the movie. It's disappointing that he seemingly died at the end of the narrative, since it would've been interesting to see him reprise the role moving forward. That said, Mysterio is known for grand illusions, and his death could well be another one.