Or, perhaps, challenge catalog.
Make an entry of an npc that would provide adversity to a specific story game.
I'm gonna try for something where there isn't an npc stat block system first.
Staff Sergeant Gerry Carlisle
Carlisle is a small weedy guy with a nervous tic that runs the black market around the barracks.
Story hooks: wants money and is willing to take a favor in return, getting short and paranoid and will pay for men to go out in his place, messing with someone else's girl.
Traits: social chameleon, shifty, math wiz.