Last week I saw a couple of questions about how to balance an NPC as a threat in an encounter with the player characters. Now as I think about it, and from the experience of my last session, there are a couple of parts to this question.
The first part is about creating the non player characters themselves. For this, I mostly say ignore the rules. If the character is important to the story you should have an idea of what they are good at and what they are not good at. Mostly they should have average attributes (they are average after all) unless there is a reason otherwise. An example of this that I used was George Viscount who was a pool shark that the players needed to get to set up a meeting with the guy that they really wanted to talk to. So how did I stat out George? He had a decent persuasion skill, but since you don’t use persuasion to convince a PC of anything, I didn’t give it a rating. The only thing that I did need to know was how good he was at pool, so I gave him a pool skill of d10. But wait you say there isn’t a pool skill, you are right, there isn’t but that was what he was good at (for the players I allowed them to make an Agility test for pool).
This was something that I picked up from my interest in the Fate system and some of the discussions that went on in that community. At this point, if the setting doesn’t have a template for the character, I would probably just give them a skill for the role. For example if I needed a simple mugger, I would give them three skills fighting, mugging, and intimidate. The mugging skill would cover things like spotting a good victim, a good location, and anything else that such a character would need to know. I have talked about some of this before here.
The second part of this about how tough an encounter is. Unfortunately there is only so much you can do about this with exploding dice and the vagaries of luck. The things that you can do are look at the players weapon damages, combat skills, and toughness and from these values make some estimates. For example if your party’s weapons mostly do 2d6+1 damage, then you know that any creature with a toughness of greater than 8 is likely to not get anything more than a shaken result from any attack that didn’t hit with a raise. The same calculations can be done for fighting. If your characters’ parry is around 5, then you know that you will only hit about half the time with a d8 fighting and you will have a raise only 12.5% of the time (yes wildcards are a little different because of their wild die, but you could still calculate the odds and the rest of the logic holds true). This is what happened with the battle in my last session, Adelaide had a parry of 5 I believe, but then she cast deflection with a raise, so that the monster needed a 8 (-1 to parry for improvised weapon) to hit. She could then go toe-to-toe with it for a number of rounds until it got lucky and things went sideways from there.
If there is some interest, I might put together some tables of probabilities for the different dice combinations to achieve different target numbers.