2. Mallen
On the off chance that Marvel feel the need to continue the Extremis angle in their Iron Man movies (perhaps with a perfected version of the virus and a subsequently more powerful wielder), they should avoid it and they should definitely avoid using Mallen. First appearing in Iron Man (vol. 4) #1 in 2005, Mallen possessed the same abilities as Aldrich Killian did in the Iron Man 3 movie, but with the added "bonus" of having claws and being able to generate electricity. The worst thing about the character, however, was that he emerged from a horrible scab-like coccoon when he first developed his powers, which would look disgusting on screen in a live action depiction. Scabs aside, Extremis has been done and shouldn't be repeated, even though I can see the temptation to use a "perfected" version of the virus as a means of conveying an increased threat to the titular Iron Man character.