To get alternate green goblin costume, play any level with the Green Goblin in it and he will have an alternate costume that looks like his classic costume more. Do this when you are using Alex Ross Spider-Man.
OsCorp's Gambit: Easy passcode. When you are downloading the password, wrap the guards in webbing and you will be able to download it. After they break out of the spider silk they will not raise the alarm if you are on the ceiling or walls.
To make Robots guards stop appearing in Chemical Chaos, after setting off the alarm many times and hiding in dark place, the robot guards will stop coming out.
In Coup d' Etat you can do the following. Select Mary Jane and stand by the spider. When the big panda balloon gets near a building. Then, you have to put down Mary Jane on the spider. In the intermission sequence, the balloon will crash into a building and will make people cry and scream!
To escape From OsCorp easily, do the following. Go to the control room on your left, where the shut off to the sentry guns is placed. Break the window and come out behind the laser wall. Exit as usually you do this and thus you will avoid the trouble of visiting the other control room.
Missing purse, go to the top of the building that is next to the building with the helicopter landing area. There you can find the desired missing purse.