WonderDrow wrote
Even if you know a superhero's weakness that doesn't make it an 'easy' win.
Sure, one could collect a lot of kryptonite as preparation for a fight with supa.
But superman is smart, so to get him in your trap wouldn't be straight forward.
And the superhero can also use your weaknesses.
In the case of Superman versus Umbrakinesis he just needs a flashlight.
Maybe keep the Kryptonite near your body? Though, even that would barely do anything.
It would be most effective if there was a villain who had powers similar to Superman (not all of them but the basics, like Superman-scale Superstrength, Superspeed, Flight, green Laser Vision, Invulnerability), but composed of Kryptonite, and capable of manipulating kryptonite, including that which composed his form. And if the show Smallville is any implication, maybe also psychically perceive, communicate with and compel folks who've come into contact with Kryptonite.
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)