In spite of the fact that Aldrich Killian was the most recent Iron Man villain - and you'd think they'd get progressively stronger - he certainly wasn't the toughest. That said, he was certainly still very powerful. What he lacked that the other Iron Man villains possessed was mobility. He couldn't fly (which makes you wonder why Iron Man didn't just take him out from afar), but was a genuine threat to Tony Stark in close-quarters combat. The Extremis virus gave him superhuman strength on a par with Iron Man, enhanced agility, a near-instant healing factor (even when limbs and appendages were lost), the ability to consciously raise the temperature of his body parts to the extent that it would melt steel and the ability to breathe fire.
