After finding out Spider-Man’s true identity and how he gained his super powers, Norman Osborn tries to recreate the process on himself, thinking that his superior knowledge and access to his ‘Oz Formula’ would get a better result. He then turns himself into the Green Goblin (with a few side effects). Thinking his experiment to be a success, he then starts to use his formula on other people, creating a goblin army. It’s now up to Spider-Man to figure out what’s going on and put a stop to the Goblin’s plans before he can take over New York. Source: Wikipedia, "Spider-Man: Battle for New York", available under the CC-BY-SA License.