First enter the cheat, ARACHNID or IMIARMAS to unlock all levels.
Start a new game and select the hero difficulty.
Once the level begins, pause the game and select exit to main menu.
Go to the Level Warp, and select Conclusion. After the Conclusion FMV finishes, press Circle to go back to the main menu again, this time go to the secret store, and you will have unlocked all secret costumes, including the Green Goblin. Now, turn the Green Goblin costume on, and start a new game, DO NOT SELECT 'YES' WHEN IT ASKS YOU IF YOU WANT TO RESET BONUS POINTS. SELECT NO. When the level begins you will be able to play as the Green Goblin, without having to had beaten the entire game on HERO difficulty.
Complete the game under Normal or Hero difficulty setting to unlock the Alex Ross costume (another suggested design for the movie) in the Specials Menu
Green Goblin second adventure
Complete the game on Hero to unlock Green Goblin. You'll now play a very unique game with an original story (over the same levels of course), which you control Harry Osborn, the 2nd Goblin as he researches his father's death.
Pinhead Bowling mini-game
Earn 10,000 points in the single player game.
Play as Peter Parker
Complete the game under Easy difficulty setting to unlock the Peter Parker costume in the Specials menu.