The Spider-Man 3 movie will be very impressive because it will feature a lot of Marvel characters, both heroes and villains.
It is clear that Spider-Man 3 is a collaboration between Marvel Studios and SONY because new information comes out every day, something much more difficult when it comes to other films that belong exclusively to Marvel Studios / Disney. In addition, what at first are crazy rumors, then are confirmed little by little.
Electro by Jamie Foxx and Doctor Strange by Benedict Cumberbatch was the first new additions to the cast of Spider-Man 3 and, from there, they have started adding characters from other sagas such as Peter Parkers from Tobey Maguire and Andrew Garfield, Gwen Stacy by Emma Stone, Mary Jane Watson by Kirsten Dunst and Doctor Octopus by Alfred Molina. While Willem Dafoe and Dane DeHaan could repeat as the Green Goblin, Charlie Cox as Daredevil and more recently Thomas Haden Church as the Sandman., have also been related to the movie. So they will surely be part of this Spider-Verse.
There will be a lot of villains.
Some time ago it was rumored that they wanted to add to Spider-Man 3 the group of villains called the Sinister 6. But the driving force behind the plot will be the relationship between Tom Holland’s Peter Parker and Zendaya’s MJ, so the rest of the characters will only make cameos demonstrating the great potential of the Multiverse. This means that instead of seeing the sinister 6 we will see a lot of villains individually threatening the protagonist.
Spider-Man 3 will include Electro (Jamie Foxx), Doctor Octopus (Alfred Molina), Sandman (Thomas Haden Church), and at least one Green Goblin (Willem Dafoe / Dane DeHaan). Others on the list are the Vulture (Michael Keaton), Morbius (Jared Leto), Venom (Tom Hardy) and not to rule out Kraven the hunter. In addition, Mysterio (Jake Gyllenhaal) could appear, since he faked his death and when the deception is discovered, he will automatically clear the name of Peter Parker (Tom Holland). Since the world now believes that he is a murderer.
In the past, it has been shown that having too many villains at once is often too much for one movie. That is why they must be very clear about everything that Spider-Man 3 will offer and give each of the villains they want to add just enough time.