I was going to suggest this as well, but when I googled it I got answers that said his suit was "hardened against EMPs" or "had 10 second restart times" (WTH?).
My alternative would be to use a powerful electromagnet to lock Iron Man down, like the ones you see on industrial cranes. It'd completely immobilize him and fry his circuitry. You could then easily kill him (assuming he wasn't already crushed inside his own suit). The only hard part would be trying to bait Iron Man close enough to electromagnet, so it'd probably need to be hidden inside a building, and you'd need like a hostage so he has to come inside rather than simply blowing the building up. I suppose the only weakness in the plan depends on whether or not Iron Man has infared vision or something and can detect, but I'm not getting into semantics.
Joshua Bright from
Trails in the Sky
Trails has a lot of powerlevel bullshit, where characters like McBurn and Arianrhod wield extraordinary raw firepower, and are therefore considered "unbeatable". That doesn't make sense when you have characters like Rean Schwarzer, Fie Clausell, and Joshua Bright, who have super speed. They can (canonically, not just in gameplay but during serious cutscenes on a consistent basis) flash step a fifty foot distance in the blink of an eye, leaving afterimages of themselves that other people focus on rather than their actual position. I'm sorry Falcom, it doesn't matter how powerful McBurn's flames or supernovas are; won't save him from a guy zipping around and stabbing him in the back in an instant. Thus, why I am curious as to if anyone has any idea how they could be countered.
I think this could be applied to characters with superspeed in general, like Quicksilver. Is there a way to defeat them?