So throw a few more ideas in, and I had one for a man who had a trifling power that could be useful -- but I knew he hadn't been experimented on by mad science.
And then I wondered -- what if he had taken some patent medicine? Mad Scientists don't have to all perform their experiments on subjects in their labs. Or perhaps one cooked up a cure in the lab and peddled it in a traveling show, not realizing what kind of effects it would have. (One rule I had already decided on was that there's no way to mass produce heroes or villains because all the mad science interacts with the subjects. Too many factors to duplicate.)
Probably would have to be less powerful than the experimental version, but might be interesting. And, of course, you can have alchemical superheroes and the like back through history.