My spiderman 3 rewrite, no venom, only the black suit, no sandman/ben parker connection:
Flint Marko and Adrian Toomes (who is now an aging old old old man will later become the Vulture) are both in the same prision cell. Toomes is imprisioned for falsifying information to make his once small company grow to emnormous proportions.
You'll have bits and pieces of funny dialogue, Adrian "They put me in this cell with a simple street thug murderer." Then you'll have Flint trying to defend his actions because he stole money for his dying daughter.
Some crazy scientific experiement demands for a human test subject. Through some sort of money bribing, these secret research agency promises large amount of money and early release for one prisoner if he agrees to BE that test subject. Marko volunteers, he'll give anything to see his daughter again. Marko suspects that he may not make it out alive from the experiment but he'll try and escape when the guards are transferring him to the lab.
Toomes wants Marko to start a riot so Toomes will help Marko save his daugther (In the movie, Toomes is shown as a super scientist of sorts). The expirement goes wrong, Marko gets turned into the sandman. Sandman creates a large scale riot in the prison. Sandman is at the edge of escaping the prison, Toomes BEGS Sandman to take him with him. Sandman agrees.
Toomes will basically lure Sandman into robbing banks to build some sort of "machine" that is promised to save Marko's daughter.
Spidey will get the black suit via the astronaut story. We'll get a big centre piece action sequence of a shuttle going 100 miles an hour down into central NY and its up to Spidey to stop it from destroying the city and also to save the astronauts (including JJ's son who is now bitter over MJ).
Spidey saves the day, but the black suit which comes from a rock escapes the shuttle and attaches to Pete unknowingly to everyone. Keep the spiderman celebration as Spidey's reward for saving NY.
Harry throughout the movie will stalk Parker and make his life a living hell, because at any moment he can kidnap MJ or Aunt May or expose his secrets to the world.
Spidey's ass is getting kicked all over the city. Sandman is too strong, Harry is takes the enchanment formula, hes making peter's life a living hell. Eddie Brock is introduced in this movie, as Parker's archrival at the bugle. The black suit finally manifests itself, Spidey starts kicking Sandman's ass. Sandman tells him "you dont understand, i need to do this for my daughter". The two are evenly matched.
In an end sequence the vulture's machine is finished and Sandman, under the vulture's orders, kidnaps Spidey (whom Vulture considers the strongest and most "youthful" specimen he can find to rejuvenate himself). Spidey is put into a machine where the Vulture promises to use spidey's amazing mutated genes to save his daguther but for some reason the vulture inserts himself into a 3rd chamber. Vulture regains the strength of a youth and is less wrinkled, hes somewhat young again but not fully.
Spidey tells Sandman that hes been tricked all along, the money was never spent in saving Sandman's daugther's life. The effects of the youth transfer is not permanent and is fading slowly, but Spidey is weakened by the procedure. The black suit is shown here to have a weakness against sonic vibrations from sound as the machine starts operating at full speed.
Sandman will brawl with the Vulture but somehow the Vulture gets the best of Sandman. Spidey is no match for the Vulture, but then Harry comes to save the day. Of course Harry dies.
At the end of the movie the suit that has made Spidey so overly aggressive and arrogant is taken off.
A humiliated Eddie Brock tries to redeem his lost job and career at the bulge by trying to expose Spidey, trying to get some better pics of him, and also he suspects that parker and Spidey are scratching each others back all along throughout the film. But the truth finally is revealed, Spidey is Parker, the black suit goes savagingly onto Eddie. Eddie Brock is sucked up into a cacoon like the victim of a Spider.
We then have an ending where MJ and Pete patch up their relationship, while crying over Harry. In in the final shot, the cacoon breaks, we have a teaser shot of Brock violently transforming into Venom.