They're not the Big Bad; they're too small time for that. Heck, they're not even Monster of the Week level. But they're not working for another villain, either, so they're not really a Mook. These are Villains whose duty is to show up for a single scene, maybe two if they're lucky, and cause some minor trouble before the heroes kick them into next week and move on to the real plot. Common varieties include Bank Robbers, Thuggish Bar Patrons, Muggers, and generally Stupid Crooks. Also known as the Lowly Criminal. See Random Encounters for the Video and Tabletop Games version of this trope.