How I Learned to Stop Worrying, Part 2: Quick and Dirty stats

Once again, I told you a story to get to a point.  Improvisation is terrifying when you're starting out, but it can be your friend once you get going.  There are several resources made to help you improvise roleplaying situations — Roleplaying Tips has an online NPC Generator or you can just download the NPC ebook, Behind the Name is a good place to look for names if you want to generate a random list, books like Ultimate Toolbox have tons of improvisational materials if you need to randomly generate things on the fly, and Zak Smith over at D&D With Porn Stars always has a ton of GMing shortcuts, typically with a Gygaxian, old-school flair.

However, when you're trying get a handle on mechanics, you may not feel confident just messing with numbers, particularly regarding some random guy the characters just decided to shake down.  Or when the characters just performed an ill-advised summoning ritual and you just realized that you didn't have a good result for when they totally botch the job.  Here are a few examples in various game systems to help you out.

Dungeons and Dragons, third-ish edition: I'm not going to recommend something when plenty of good word count has already been devoted to it.  Once again, Zak Smith at D&D With Porn Stars has something that might be useful to you in this article.  It won't make balanced encounters, but it'll feel right enough that no one cares.  If the PCs shake down a shopkeep who isn't skilled, give him a handful of hitpoints (maybe a d4 or so) and a +0 to do pretty much anything (maybe he has a +2 to talk to people).  Give the PCs a head full of shame for shaking down defenseless villagers.  Also, feel free to give big stats to mobs (in D&D 4e, unruly mobs are level 5 creatures).

Dungeons and Dragons, fourth edition: The books themselves give you the tables to make monsters by role and level (it's in Dungeon Master's Guide 1, but I don't know where you find it in Essentials).  The most recent version of the rules can be found here (the table in Dungeon Master's Guide 1 is still usable, but is "out-of-date" with the latest version of the rules), and if you don't feel comfortable with the numbers (and don't want to pay for a D&Di account), Asmor.com has a program that lets you make stat blocks and a website that does all the math for you.

World of Darkness, whateverth edition: There's a quick and dirty way to do NPCs in the Predators book for Werewolf: the Forsaken.  Basically, an unskilled character should roll two dice, a skilled one should roll three or four dice, a professional in the field should throw six dice, and a truly gifted performer (we're talking Olympic athlete or prodigy scientist) should roll eight to ten dice.  More than ten shows supernatural ability.  In terms of Attributes, two is average, so rolling two Attributes together will probably be around four dice for an average person.  Seven points is average health (five or six is dead minimum), and goes as high as ten in, say, a truly gifted endurance athlete.  More than ten displays supernatural fortitude.  Feel free to add the typical modifiers, as noted.
Also note that this works in old World of Darkness (pre-2004).  Two is still average, but dice are a little more common (individual successes don't mean as much in the old edition), so maybe bump dice pools by a die or two and you'll be set.

Deadlands, classic: Bigger dice are better.  More dice are good, but slightly less better.  2d6 is average in a Trait; you're professional at your Aptitudes at a skill of 3.  The die type is tied to the governing trait, so a klutz can be a practiced gunslinger, but he's still only rolling 5d4.  Four is a pretty good number of dice to represent high proficiency.  Use wounds as normal, or (for quick and dirty wounds in mooks that go down fast) multiply size by five to make hit points, and ignore hit locations (though you should still roll to chart the extra damage from shots to the guts or head).

Call of Cthulhu: How often should the NPC succeed at a skill?  That's his percentage.  Human professionals probably fall around 50% or higher.  30% is more typical for dabblers.  Average hit points fall around 12 or so.  Gods rarely (if ever) miss, and typically don't use skills (not in the way that humans understand), so give an attack at 100%.  Cthulhu has stats, but if everyone meets Cthulhu, they're probably dead.  The one who took the least sanity loss survives.  Maybe.

Unknown Armies: The average stat is 50%, and they typically range from 30% to 70% (less and you're disabled, more and you're an Olympic athlete, a genius, a popular motivational speaker, or a powerful occultist).  Professional skills fall around 30%.  Someone just learning a skill has about 10%; a person expert in the field is probably around 50%.  Going above 60% probably represents someone who is known in the field — a published scientist, skilled doctor, noted marksman, or gifted athlete.

I might do some other systems in the future, but those are the ones with which I'm most familiar.