Iron Man and Spider-Man's nemesis Green Goblin have been pitted against one another multiple times over the years, especially during the events of the "Dark Reign" storyline. But while Norman Osborn has stolen plenty from Tony Stark over the years, one variant of Iron Man from 2015's Secret Wars got the chance to return the favor.
Secret Wars: Spider-Island (by Christos N. Gage, Paco Diaz, Frank D'Armata, and VC's Travis Lanham) transformed a lot of heroes into new forms -- including giving a variant of Tony Stark the Goblin Serum, quickly turning Iron Man into a uniquely heroic but doomed version of the Green Goblin.
How Secret Wars Turned Iron Man Into Spider-Man's Green Goblin
As a result of Secret Wars, the remnants of the Marvel multiverse were recreated into the patchwork planet known as Batteworld. Each "realm" was based on a different reality. Some of them reinvented classic Marvel concepts in new eras of genres, such as the wild west variants of 1892 or the Martial Arts-inspired Masters of Kung-Fu. Others directly drew on specific storylines, introducing realms where a classic storyline had taken a different turn. One of these realms was known as Spider-Island and was derived from the crossover of the same name. In this realm, the heroes had failed to prevent the Spider-Queen from infecting most of Manhattan with a transformative virus that put the populace under her control. Only a handful of figures proved capable of resisting the virus completely.
Others who suffered from other transformative states (like Werewolf by Night) could break free of the Spider-Queen's command while in their altered states. This resulted in the remaining heroes exposing what few others they could get to new states, giving the Hulk the Lizard Serum, turning Captain America into a werewolf, and changing Captain Marvel into a Living Vampire like Morbius. While the heroes also freed Iron Man, it came at a cost, as the only means left to free Tony Stark involved the Goblin Serum created by Norman Osborn, effectively turning Iron Man into a new version of the Green Goblin.
What Happened To The Iron Goblin?
Tony Stark's willpower and inventive nature allowed him to briefly adapt to the situation, even incorporating Green Goblin elements and weaponry into his Iron Man armor. This corrupted Tony played a vital role in giving the heroes an edge against the Spider-Queen -- which eventually led to the fall of her regime. However, Tony never saw that happy ending. Feeling his grasp on reality waning as the Goblin Serum took further effect, Iron Man elected to stay behind when the Spider-Queen's forces cornered the resistance. Taking up the Ebony Blade as an additional weapon, Iron Man chose to sacrifice himself to cover their escape -- making sure to die as himself instead of devolving into the same maniacal villainy that often defines Norman Osborn.
The death of the Spider-Island Iron Man touches on a lot of elements of Iron Man's history and his connection with Norman Osborn. Iron Man specifically references Norman Osborn's Iron Patriot armor when stealing Goblin technology, returning the favor by utilizing stolen tech for his own purposes. Tony is forced to concede that Osborn's inventions have a certain flair that he could never match. But even Tony's mind couldn't withstand the full effects of the Goblin Serum, which quickly turned one of the most brilliant heroes left in this realm into someone always on the edge of betraying his friends and allies. Luckily, Tony was still very much Iron Man at heart and got the chance to die as himself instead of just another Goblin on the warpath.