ASM2 - Quentin Beck/Mysterio - Former failed actor/magician/entertainer turned criminal.
Movie opens with Beck using his standard magic and deception to rob a bank, before his plan is spoiled by Spiderman. He goes to prison, sees the fame Spiderman receives, becomes jealous and obsessed. While in prison, he gets into voodoo and the dark arts, learning "real magic."
Meanwhile, Oscorp uses Dr. Connors' formula to move onto a cure for cancer (Norman's terminal illness). The first formula helps Osborn some, but leaves him with skin legions and minor deformities (think Dr. Connors' skin issues in ASM). They enhance the forumla use test subjects from an asylum from for their human testing trials, including Quentin Beck and a deranged serial killer named Cletus Cassidy. This new "formula" is much more than they bargained for and kills the first subjects it's tested on. However, one of the scientists running the experiments grows a fond spot for Beck, due to their similar beliefs in the occult (think Red Skull, magic vs science) and helps him escape so he won't suffer the same fate as the rest of the subjects. These two leave and begin to plot against Spiderman.
After their adventures and ultimate defeat, we pan back to Oscorp where they begin their testing on Cassidy, the last remaining test subject. Cassidy not only survives, but embraces this new formula, or symbiote as it has grown to become.... hence the creation of Carnage.
In a final scene, we see Norman Osborn deformed and angry from the failed attempt at his cure, growing more and more insane. He breaks into the weapons research wing of Oscorp and steals the Green Goblin equipment we all know and love.
ASM3 - Carnage/Cletus Cassidy, Green Goblin/Norman Osborn
Carnage is the primary villain, Green Goblin's character continues to grow and develop until he hits full goblin insanity around the midpoint of the movie. Spiderman defeats Carnage, but Green Goblin actually gives him the final blow, seeing him as an uncontrollable loose end.
Goblin discovers Parker's true identity, infamous Gwen Stacy death around the climax of the picture (leave it completely open to interpretation, you never truly know how she dies or who's responsible), Goblin dies similarly to the comic ending, but not exactly the same, as to avoid the Raimi picture.
In the final sequence, we see Peter, at peace, but still struggling to cope with Gwen being gone, when his newfound friend Mary Jane shows up. They embrace in a hug to console each other with their friend's death.... fade to black. Fade in to the typical "I'm Spiderman" swinging scene. End.
That's basically my idea. no details filled yet, but you get the broad stroke.
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