I saw on the internet a way to unlock this, but when i did the same: started a new game on super hero, quit the game, entered ARACHNID in cheat menu and watched the cinematic. but when i came to the store Goblin wasn't unlocked. If anyone knows how to fix this, please help me. This is where I found the cheathttp://www.cheatscodesguides.com/playstation-2-cheats/spider-man-the-movie/
Spider-Man: The Movie Play as Green Goblin
Start the game on hard or super hero difficulty and get into the first level. Use the pause menu and quit out to the main shell. Enter the "ARACHNID" cheat in the cheats menu which will open up all levels. Use "Level Warp" to go to the conclusion level. This is only the final cinematic where Norman reveals himself to Spidey and is taken out by the glider. When you play this cinematic you have essentially beaten the game on whatever difficulty you chose at the beginning. Get back to the main menu and enter the "Secret Store". Turn on the Green Goblin. Use "Level Warp" or just start a new game and you will be playing as the Green Goblin. You will be playing at whatever difficulty you chose at step one unless you choose to start a new game and select a new difficulty.