It’s hard to believe it’s been 10 years since Iron Man 3 was unleashed in theaters, and even though it’s been a hot minute, fans have some questions regarding a few loose threads left in the film.
One fan on the Marvel Studios subreddit was particularly interested in what happened with the experimental serum made by Aldrich Killian known as Extremis. The scientific breakthrough allowed those injected with it to heal all kinds of traumatic wounds and deformities — it even repaired psychological damage.
The serum was tested on ex-military, and for those it worked for, they were able to regrow limbs and gain some powers. There was one notable drawback — there was a slight chance the body would reject it, resulting in the subject exploding. However, Tony Stark was supposedly able to stabilize it somehow, which works for the plot of Iron Man 3, but leaves all kinds of questions unanswered for the rest of the MCU.
While we haven’t really seen the MCU make use of Extremis again, it has popped up occasionally. Most notably, it was a crucial plot point in the first season of Agents of S.H.I.E.L.D. in which it was combined with Gamma radiation and Chitauri technology to make super soldiers. However, the general consensus is that Agents of S.H.I.E.L.D isn’t really canon in the main MCU anymore, so that means we still haven’t been given an explanation as to what happened with the Extremis serum. According to one fan in the thread, someone with Extremis does make a small appearance in Shang-Chi.
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by u/TrueLegateDamar from discussion What Happened with Extremis?
in marvelstudios
Most theorized Stark reverse-engineered it and then it was dropped like many other useful things the MCU has a habit of forgetting. Although it’s also been speculated that it could return in the upcoming Thunderbolts movie as it could be mixed with Hulk blood to give us the Red Hulk.
However, as the original Reddit post asks: if Stark had managed to stabilize the serum, then why didn’t they keep the perfected version? It would have come in handy multiple times, and yet it’s never really mentioned by the heroes again. It’s a question we’ll likely never get the answer to.
As the MCU grows, it seems some plot points will inevitably be left behind, but Marvel has used characters and plot devices years after fans thought it had forgotten them. For example, Abomination made his long-awaited return in Shang-Chi almost 15 years after The Incredible Hulk. Other characters like Harley Keener, also from Iron Man 3, showed his face at Tony Stark’s funeral. Marvel has shown that it does keep track of its own continuity sometimes, and although it might seem like something’s been forgotten, it could always be brought back again. We can only hope all of our questions will be answered in Thunderbolts.