10 MCU Plot Holes That Aren't Actually Plot Holes
3. Extremis Saves Pepper, But Tony Never Uses It Again - Iron Man 3
At the end of Iron Man 3, Pepper Potts falls to her death - or so we're made to think. She actually survived the fall thanks to the Extremis virus, a technology that can heal people, make them stronger, and even regrow limbs.
Tony removes the virus from Pepper in order to make her 'normal' again, and... it hasn't been seen in an MCU movie since.
But if Tony was familiar with this technology and could use it for good, why does he just leave it alone? Couldn't Extremis be used to help out Rhodey after his injury in Captain America: Civil War?
That might seem like a logical choice, but bear in mind that Extremis is also capable of blowing people up. That seems like a big enough factor to deter Tony from using it further, which explains why he hasn't messed with it since Iron Man 3.
How does Tony know how different bodies will react to the virus? How does he know that one person won't explode while another thrives? He doesn't.
Extremis is a risk, a risk that a post-Iron Man 3 Tony - someone focused on bettering himself and helping others, more so than ever before - would not be willing to take.