I've got a 2-person party and i'm having some difficulty with balancing encounters for them. It seems that what i'm making is either way too easy, or harder than i really want it to be (ie, they're either not using much of their stress tracks or they're taking higher consequences). I didn't see it in the books, but maybe i missed it. Is there any formulaic way of creating encounters for players (specifically 2 players)?
Yes, this is in the Your Story book. I'll get page references for you ASAP, but there's a whole section on building opposition based on the total refresh of the party and whether they're mundane or supernatural.
I just wrapped up a 3-novel series that started with a pair of wizards and I discovered early on that the key was to get the to the point where they had used enough mental stress that they were forced to make hard choices. Choices like "Do I cast a shield big enough for everyone and force myself to take a mental Consequence? Or do I just protect myself and avoid it?" When the wizards were joined by a Knight of the Cross, I had some physical badassery to contend with, too.
Here are some tips for running DFRPG combats:
Minions are awesome. They're a very flexible way to tune the difficulty of an encounter on the fly, seamlessly within the fiction, without seeming to fudge or cheat at all. Example time!
The PCs are finally bringing the fight to the vampire lord who's been striking at them from the shadows for the whole game. But the vampire lord isn't the whole fight, he's got minions!
Need to burn some mental stress for your wizards? Most Rotes aren't area-effect or multiple-target spells, they're 1-stress attacks and defenses. So a handful of minions can force a wizard to burn their higher stress slots either in a series of Rotes or by forcing them to dig deeper to hit more than one minion at a time.
At the same time, you can be flexible in your use of minions to tune the difficulty. Is the party sufficiently burnt so that the vampire lord will be a challenge? Then don't make them all fight to the death! Let some flee after taking damage - or seeing their compatriots harmed!
Don't forget that fights all take place somewhere. And in any fight, enough energy (mundane or arcane) is being flung around to cause problems in that environment, whether on purpose or by accident. Environmental aspects afford you the opportunity to make your PCs burn stress and the flexibility to aid your bad guys in attack, defense, or escape.
I want to refer you to some concepts I presented in another answer about how the opposition thinks. The main point though, is to remember that the bad guy is fighting for his life and / or freedom against the PCs. He (or she) will use everything at his (or her) disposal to defeat them. There is no such thing as "too devious" in a situation like this. They'll cheat. They'll trick. They'll leverage PCs loved ones to give themselves the upper hand. If the bad guy is bad enough that it takes a wizard or a bunch of werewolves or whatever to handle him (or her...you get it, right?), then he's not going to leave any avenue unexplored, any asset unexploited.
Play the opposition like it's life and death. Fight hard. Fight dirty. Fight tooth and effing nail.
It Seems Harsh, But...
Your players will thank you for it. My players will take an easy win, sure. But the games they talk about, the sessions that add entries to our private lexica, are the ones where they won hard. The ones where they bled. The ones where they ended up with physical and mental consequences - mementos of their struggle. The ones where it looked like it could go against them right up until the very end.
They'll hate you while it's happening. And they'll love you when it's over.
Don't be afraid of easy. Don't be afraid of hard. They will enjoy the gimmes and learn to run from or be creative with the hard ones. Unlike That Other Game, the point isn't to fight everything, so balance is beside the point.
Make it interesting, make "defeating" the encounter not assumed by the plot, and play to see what happens.
The players will enjoy being able to decide what to do instead of having the "right" outcome pre-determined, and you'll have the opportunity to be as surprised as the players are by where the story goes.