The league of evil are, for some unknown reason, kittens. Cute fuzzy little kittens, who, for some unknown reason, desire to kill superman.
That's the whole scenario.
On the first run, I put together little hint sheets of what things each kitten knows about superman and what personality they had and... (I even had rules - if, using the advantage system, they could amass 6 triples (reroll 6s to get human level success, reroll again to get super success, now beat superman) No. This is a mistake.
The only thing you need to say, after the intro, is, in an incredulous voice: "How? You're kittens." (Well, not quite - sometimes you need to say: "Ok... so then what?" and sometimes you won't be able to stop ourself from saying "What? WHAT?" in increasingly desperate tones of voice as your players plans get sillier and sillier.)