This takes some people by surprise, but NPCs - despite being under the GM's control - are not capable of seeing stat sheets. On first meeting an NPC should have no clue as to who has what strengths in a party aside from what appearances dictate. This means that the NPC must take time to learn who the PCs are and what they do. It also means that the PCs can take measures to appear as what they are not, and in some cases someone without the mechanics to back up a role may be assumed Today I want to talk about that, and what it can mean for your game.
Who Is The Face?
The place this most often comes up in games is when interacting socially with an NPC. Parties almost always want their best set of social dice doing the talking because if a roll comes up you want the highest chance for winning. This is so strong that in some games - like Shadowrun - being "the face" is a job in and of itself.
But how is a new NPC supposed to know who the face is, and thus who they should talk to? I mean, sure, there are some clues. You find 4 people together in a D&D world and one of them is half naked, covered in scars, tattoos, and muscles; one is wearing heavy armor and more weapons than an armory, one is covered in books and scrolls, and one is carrying a lute and a clever smile well, it's not hard to pin the bard.
What about other situations? What about actions? What if the contact is for "an armored man covered in weapons"?
In a game I'm in, my PC is regularly asked for the status of new NPCs the group meets from other NPCs. My character, until recently, had no social skills. So why did it happen? Well, the people with social skills were around, but they didn't take the same interest in people my character did. To the other NPCs my character was the outgoing one who would talk to folks, find out what ailed them, and try to help.
Where Is The Threat?
In your game of choice, who is the biggest threat in the party? Now, I don't mean "the wizard" in D&D. I mean in a specific game, which PC is the most dangerous character? Why do you think that? Are you considering stat lines? If the characters have the same amount of XP shouldn't the characters all be about balanced? And yet, you probably had someone in mind.
In my Star Wars game, I'd say the most dangerous PC was the chiss. I say this despite the fact that another PC was just as good mechanically. The difference was in how the two characters were played. In my L5R game I'm honestly not sure. In a fight it is probably the Hida bushi, but outside of one? It could be anyone Finally, in my D&D game I'd say it was the Warlock. He has a bag of tricks and knows how to use them. It's probably enough to give him the edge over any other PC, though by the nature of D&D and the low level of the game, he has close competition.
This same thought process is something your NPCs will have to go through as well. Sure, the worlds will have some rules. In Star Wars you prioritize Jedi because they are very dangerous. Killing the mage/cleric is another common tactic in D&D. But some parties will transcend that. Especially since NPCs don't understand that Sarah just had an incredible round where she dropped 3 nat 20s. They just see a Barbarian wiping the floor with something that was big and tough. Which brings me to my next point...
Is It Luck Or A Plan?
One of the few moments I liked across all the Pirates of the Caribbean movies is the constant wondering if Jack Sparrow just gets incredibly lucky, or if he plans it all out as he goes along. The 4th movie suggests it is a plan, but slippery writing makes some of his plans more Xanatos Roulette's than Xanatos Gambits really.
Consider in your game though. What do the NPCs have to go on? Sure, one improbable shot from a Critical Success could be pushed off as luck. What about two? Three? What is the reputation the PCs get as they escape death defying situation after situation? As they complete adventure after adventure, always coming out on top? Sure, they may act like goof balls on occasion and in towns, but to the rest of the world - even if they keep succeeding from luck alone - it doesn't look like it.
No enemy, especially a combat enemy, is going to assume that something that fortuitous just happened and not consider that it was planned for.
Look at the events of your game. Strip away the fact you know your group was probably just improvving and doing what they could think of at any given moment. How does it look to the rest of the world? The people who don't know how much was desperation. The people who don't know how much was luck? Pretty scary, right?
For a more game divorced perspective, we know in Die Hard that John scraped, struggled, and lucked his way through that encounter. To the outside world, one man took out that entire group of terrorists and saved all the people inside from a rooftop bomb. Even if John says he was lucky, you know people aren't thinking about it as "he killed one guy, then another, then got lucky with a third" they're thinking "this guy with just a pistol and no shoes took down a dozen heavily armed men that had control of the building."