* Green Goblin (Norman Osborn): This is the main villain and is playable from the start.
* New Goblin (Harry Osborn): You unlock Harry as a playable character by completing the game's story mode.
There are no other playable goblins in the game.
It's important to note that Spider-Man 3 (2007) is a single-player game. There are no multiplayer modes where you can unlock new characters.