In the second sequel of the Spider-Man Trilogy, Peter is finally living the life he wants. New York doesn't seem to be gunning for him, he's with the girl of his dreams, and he's managing to balance his normal life with the life of Spider-Man. But his overconfidence leads to tension with MJ when he begins flirting with Gwen Stacy (Bryce Dallas Howard); and Harry Osborn, having discovered that his best friend is Spider-Man, decides to take his father's Goblin serum and seek vengeance.Meanwhile, escaped convict Flint Marko is turned into the shapeshifting Sandman (Thomas Haden Church) after entering a particle accelerator, and is revealed to have been involved with the same criminal who killed Peter's Uncle Ben. As well, a mysterious alien organism crashes to Earth and bonds with Peter, enhancing his powers but also influencing his behavior for the worse. When this symbiote is abandoned, it finds refuge in a rival, Eddie Brock, Jr. (Topher Grace), who becomes the maniac Venom.
Advertised Extra: Venom, though a possible subversion as well. Venom was only in the movie for about ten minutes, but he surprisingly did a lot in ten minutes: He teamed up with Sandman and kidnapped Mary Jane, which led to Peter and Harry's reconciliation, which led to Harry's death, which led to Peter and Mary Jane's reconciliation. Basically, the plot couldn't have wrapped up without Venom taking action.
This really depends on whether you think of Venom as the combo of Eddie and the symbiote, or just the symbiote. From the idea that Venom is really the symbiote, only needing Eddie as a tool for revenge, then Venom has a lot of scenes, just no dialogue.
Anti-Villain: Sandman, who became a criminal in order to steal money to save his sick daughter.
A bit of a subversion, given that he has no qualms about pulverizing cops trying to rescue his completely innocent hostage.
Arson, Murder, and Jaywalking: In MJ's words regarding a possible relationship between Peter and Gwen: "How come you never mentioned her? She's your lab partner, you saved her life, she thinks you're a genius, and she had her polished fingernails all over you?"
Became Their Own Antithesis: After encountering the symbiote Peter goes through this and recovers once he realizes what it is doing to him and how he affects some others. It is still hinted that his behavior came from an internal desire to act this way.
Big "Shut Up!": Harry to Peter after Peter tries to explain that Norman accidentally killed himself. He either thinks he's lying or doesn't care since he always resented Peter.
Bittersweet Ending: Leans more towards the positive side: Harry is dead but made amends with Peter, and Peter has to come to terms with having acted like a colossal jerk, but he's managed to overcome his dark side, forgiven the man who (accidentally) killed his uncle, and it's implied that his rocky relationship with Mary Jane will heal, and they'll be back together again.
Casting Gag: In this film, Mary Jane, a redhead is played by natural blonde Kirsten Dunst, whereas Gwen Stacy a blonde is played natural redhead Bryce Dallas Howard (daughter of Ron Howard)
Chekhov's Gun: Peter discovers that amplified sound (i.e. standing next to a ringing church bell) disrupted the symbiote long enough for Peter to remove it. He uses the same tactic during the final battle.
Comic Book Movies Don't Use Codenames: Venom is never named at all. Likewise, Harry's costumed identity was referred to as "New Goblin" in promotional materials, but he's never even called that during the film. However, Peter does taunt Harry by calling him "Little Goblin Junior" at one point, which is the closest they come. This was barely averted with Flint Marko who gets called "the Sandman" exactly once during a broadcast.
Deus ex Machina: The butler suddenly revealing the true nature of Norman's death to Harry. Word Of God states that he was supposed to be a hallucination, representing Harry's good side, but he's seen interacting with Harry in Peter's presence, who doesn't act as if anything's wrong.
Eagleland: Type 1. There was no sense whatsoever in Spider-Man landing in front of the American flag right before the final battle besides a patriotic money shot.
Executive Meddling: It's common knowledge that Sam Raimi had no intention of putting Venom in the film, but was forced to by Sony because of the character's popularity.This was in direct contrast to the first two films, where Raimi had complete creative control.
Foreshadowing/Call Back: In their earlier chase/battle, when Peter throws one of Harry's bombs back at him, he's not trying to hit Harry, but merely wants to distract him long enough to knock Harry off his glider and get away. Their fight later on in the movie ends with Peter doing the same thing, and thanks to the symbiote Peter's wearing, he's not nearly as nice about it.
Four Lines, All Waiting: One of the more common complaints about the movie was the fact that the presence of three major villains, each of whom has their own plot, as well as the romance plot, left the movie rather crowded.
Reckless Gun Usage: How Flint killed Uncle Ben. He was startled when Dennis Carradine came running over.
Retcon: Whoops, turns out the guy Spidey killed in the first movie didn't kill Uncle Ben after all, Sandman did! We never see Uncle Ben getting shot in the original, but it still gives no indication that there was more than one robber involved.
Series Finale: During development, the filmmakers weren't sure if there was going to be a Spider-Man 4, so they designed movie 3 to act as a series finale if need be. In retrospect, it seems to have been a wise choice (Sony wanted a movie as quick as possible, but Raimi couldn't give a script that fully satisfied him in time; a reboot came instead)
Shipper on Deck: She may like Peter herself, but Ursula is still all for him and MJ.
Temporarily A Villain: While he doesn't quite become a full-blown villain so to speak, Peter shows a semi-evil side when the symbiote he has on his suit results in a major increase in vengefulness and aggressiveness. He doesn't switch sides; he's fighting against the same enemies as he was immediately before; but the symbiote's influence has him doing things he severely regrets and that the series portrays as very clearly wrong.
Vehicle Vanish: Harry pulls a particularly goofy one on Peter; Peter is looking through the diner window at Harry, who is sitting, smiling at him before vanishing in such a way that it simply looks like he threw himself to the floor.
Well Done Son Guy: Harry clearly still has daddy issues, and Peter takes advantage of this to get one seriously devastating dig at him.
Well-Intentioned Extremist: Sandman genuinely wants to do good by helping his daughter out of her illness. Unfortunately, he has to steal money from various places as well as commit Accidental Murder of Peter Parker's uncle in order to do so.
What the Hell, Hero?: Gwen gives this to Peter in the restaurant scene, when she realizes he's only romancing her to humiliate Mary Jane. She even apologizes to MJ before storming off.
Eddie Brock actually calls out "What the hell?!'" when black Spider-Man breaks his camera. He improvises: he takes out his digital camera and snapping some quick photos of the carnage as th police arrive, then downloads the images to his computer, takes one of Peter's Bugle images of Spider-Man in Times Square, Photoshops Spider-Man into one of Brock's own images, and recolors him black. This comes back to bite him when Peter exposes him, forcing J. Jonah Jameson to fire him.
Possible Actor Allusion, as Grace's character in That 70's Show frequently yells this line when his friends mess with him.
Within Parameters: The scientists running an experiment involving a particle accelerator and sand notice that the weight of the sand is greater than expected. They write it off as a bird that will fly away once the experiment starts. The "bird" is actually Flint Marko, about to be turned into The Sandman. I want to know exactly what sort of 200-pound bird the scientists were thinking of.
Brilliantly parodied in this video. For brevity's sake, just jump to about 1:50.