You're running your game and then your players end up in an encounter. Maybe they're up against a plot-related enemy and maybe it's just a random encounter. But you haven't prepared stat blocks or anything you need for combat. You know that combat is complicated and requires special balance to keep things from being too easy or too hard, so how can you create something balanced on the fly? The surprising answer is that you can create an encounter very easily if you keep a few things in mind.
The first thing you should decide is what type of enemy your players are facing off against. For a story-based encounter, this is easy enough: you want the enemy type that is most involved in your campaign. For random encounters, you can make the decision based on the same idea, but you can also mix it up if you feel like it. What matters is that you're getting a baseline of what your enemies are capable of.
Then you want to determine the number of enemies involved. Is it a single foe, a party, or a horde? This will depend on the type of enemy you selected to begin with. Your BBEG fight will likely be a single enemy, a party of rival adventurers or monsters will be somewhere in the middle, and a horde will feature less powerful enemies. For the purposes of most encounters, you want to select one of these three options. There is a basic mathematical relationship you want for each one, and it's straightforward. [I will address armor class after discussing these other considerations.]
- A single enemy should have twice the hp of the party's average character; they should be more likely to hit by a small number (if the party averages +5, they should be +7/8); and they should deal about twice as much damage as the average party member.
- A party should be roughly equal to your players' party: slightly less hp (10%-25% less), slightly less likely to hit (if the party averages +5, they should be +4), and about the same amount of damage.
- A horde should be about twice as many as are in the party: half the hp of the party's average character; a half less likely to hit (if the party averages +5, they should be +2/3); they do about half as much damage as the party's average.
These numbers are rough and largely approximations. You can use the official mathematics to find the exact balance according to the game books, but we have another trick up our sleeve: fudging rolls. We can use that tool to moderate any imbalance in our combat. More on that later. For now, let's look at an example of each possibility with real numbers:
Single enemy: Your players have found themselves a young dragon and are itching to fight. You can look up dragon stats if you want, but if your playstyle is storytelling-based rather than combat-based, you'll want this dragon to be an appropriate challenge more than you'll want an actual dragon's kind of challenge. So let's say our average player in the party has these vital stats: 55 hp, +6 to hit, and 1d8+3 damage (which is about a 4th-6th level character, appropriate for a young dragon fight in the first place). So we'll follow the doubling formula and end up with these stats for the dragon: 100 hp, +9 to hit, and 1d12+5. I dropped a few hp from the dragon for a clean 100 hp--this is in part because 100 hp is a large amount we rarely want to go over. I selected +9 to hit because it fits in our formula and because it means that the dragon is likelier to hit than to miss, which makes it a challenging foe. And I expanded its damage not by a complete factor of 2, but by a step less than double--there is no d16 in standard dice sets, so we go for the next down, and the +5 is a step up from +3 without overwhelming the players. Now we have the vital combat information for our dragon, and it only took a moment. You would be able to design the stats for this encounter in less than a minute and be able to keep rolling with the game.
Party: Your players have been running up against a rival band of adventurers for days and the tensions have finally boiled over. You could use a handful of pre-designed characters or the numbers provided for specific enemy types from the game books. But you could also just slap together the stats for a bizarro version of the party. We'll keep our numbers from the last example: the average player as 55 hp, +6 to hit, and 1d8+3 damage. So our rival party has variations on those numbers. Let's say the player party is three characters. So our rival party also has three characters, with these numbers: rival adventurer 1: 50 hp, +5 to hit, and 1d8+1 damage; rival adventurer 2: 52 hp, +4 to hit, and 1d6+4 damage; rival adventurer 3: 45 hp, +4 to hit, and 1d8+2 damage. Each of these numbers is slightly below the party's on average--our goal is to create an almost equal but still winnable fight using our bizarro version of the party. I suggest directing these party-sized combats as though the players are fighting themselves--one rival adventurer could use similar tactics to a certain player character. Or you could try out strategies you're interested in. What matters is that as the players fight, you track the momentum as you go. More on that shortly.
Horde: Your players have entered a dungeon which appears to be inhabited by kobolds, who become defensive and territorial when they come in. You could use kobold numbers, but how many will you include to strike the right balance? I suggest that instead, you use the formula given above. Our players still average the same numbers: 55 hp, +6 to hit, and 1d8+3 damage. There are still three players, so our formula says we need 6 kobolds for the combat. Their numbers will be about half the party's:
Now we have the same numbers are our first two encounter types, but reorganized for more creatures. You'll notice that the total hit points in each step are slightly different--all the kobolds combined have more hp than the dragon, so aren't they a greater threat? But we still haven't addressed the final vital stat for combat: armor class.
I decided to leave armor class for last because it's a delicate number. Whereas you can fudge any rolls involving to hit and damage, armor class is a set number which can't be changed mid-combat without some serious fudging. So you want your armor class to be a little more carefully considered than how many hit points a character has. I say that generally, you want your armor class to reflect how long you want the combat to last. A higher armor class means more misses by the players, which means more time in combat, which means more damage taken by the players' characters. But you're throwing this encounter together off the top of your head, so how do you get it right?
I recommend a simple sliding scale. It involved taking an enemy's to hit and damage into consideration. There's a mathematical way to do it and an estimating way to do it. The mathematical way say to start with their to hit. Let's assume that our party averages a 14 armor class, which is pretty normal for most parties. That means that a +4 to hit would mean striking the players about 50% of the time. (That's the number for our party of rival adventurers, so let's run with it.) Their average damage (at 1d8+1) is 5 or 6. At 50% of the time, that means that rival adventurers will deal 2.5-3 damage per turn. Our players have about 55 hp, so they should be able to withstand about 20 rounds of combat before ending up seriously hurt. Now we run this number back through our other player information: 20 turns to go through the rival adventurer's 50 hp means the players should average about 3 damage per turn to stay ahead, and we know they average 7-8 damage per successful strike, so the players should successfully hit 1 out of 2.5 attacks. If they have a +6 to attack, then the rival adventurer's armor class should be about 16 or 17. So we can give the rival adventurers armor classes of 16 or 17, and we have a balanced encounter.
We could do the same math on the young dragon and kobold examples. Young dragon: +8 to hit and 1d12+5 per hit means that an armor class 14 would take 11-12 damage roughly 75% of the time, or about 9 damage per turn. At 55 hp, the players can safely take damage from the dragon for 6 rounds. The players need to go through the dragon's 100 hp in 6 rounds. There are three adventurers, so this is really only 33hp in 6 rounds per character. This is roughly 5 damage per turn, and they deal 7-8 damage on a successful strike, so they must hit roughly 2 out of 3 attacks. With a +6 to attack, the players will strike successfully that often against an armor class of about 13. On the other hand, the kobolds: +3 to hit and 1d4+2 damage means an armor class 14 would take 4-5 damage a little less than half the time, which is about 2 damage per round, but from 6 kobolds total. Since we have twice as many kobolds as adventurers, we double these numbers; the average player character takes about 4 damage per round from the kobolds as a whole. The player characters have 55 hp, so they can take 13-14 rounds of combat from the kobolds. So we take the 14 rounds and the kobold's collective 150 health and find that the player characters need to deal about 10 damage per round collectively, or 3/4 damage per player per round. (Eliminating kobolds from combat will shift these numbers, but not enough to throw things off completely, and you can always fudge things.) The players deal 7-8 damage per successful strike; the players should be facing a kobold that allows them to hit every other turn. With a +6 to attack, we want armor classes of about 16 to keep combat balanced.
But that was a lot of math to do, especially on the spot when improvising an encounter. If you improvise enough encounters, you'll get a feel for how to do this without breaking out a calculator. But in general, here's a simple rule to allow you to do this without much effort: For party- and horde-sized encounters, if you're using the formula I showed you above, you can just take your party's average bonus to attack, add it to 10, and make that the enemy's armor class. That will give your players about a 50% chance to hit the enemies, and the balance of the rest of the numbers will suffice to keep things even. For your occasional lone enemy, cut your players' average bonus to attack in half and add it to 10. If you're using the above method for doubling their vital stats, this will mean that your player characters will hit the enemy about two-thirds of the time, which will create a tense combat. These shortcuts will get your started, but they won't carry you through the encounter.
Other features of encounters can enrich the experience for your players. Interesting terrain or distinct strategies can make things memorable; consider which is more interesting, a scrap with some bandits in the woods, or a scene in which bandits scale makeshift walls to fire projectiles down on the party before leaping down on top of them? You can also give the enemies access to artifacts and magic items which will affect the way that they fight. The momentum of an encounter can be exciting too; perhaps you spring one on the players just as they're beginning to feel safe or in a part of town where combat shouldn't be happening. What matters here is that an encounter feels like a unique and valuable part of the game and story, not just a way to get experience and loot.
Finally, as I've written about previously, it is often a great idea to fudge rolls. Encounters, whether devised by the guidelines above or improvised or taken directly from a sourcebook, are inherently random, and sometimes things will go awry. But should a few unlucky rolls mean that the players are stopped dead (literally) in their tracks before completing their adventure? Wouldn't it be meaninglessly tragic for a random encounter to be the end of a years-long campaign? I think that fudging rolls is an important part of walking the line between telling a story and running a random simulation. So as I describe in this previous article, it is a good idea to soften the blow of random chance with some fudged rolls.
Let's say you've done some quick math, improvised your encounter, and now your players are floundering anyway. They had some unlucky rolls and now the BBEG has rolled a critical hit on a player character with little remaining health. The dice say the damage is enough to outright kill the character. But you have no plot reason to do so, so you fudge the roll. Maybe the BBEG failed his attack, or rolls incredibly low on damage, or directs his attack at a healthier player character. You can adjust here and there as you go to keep the momentum going in the right direction.
The most obvious issue here is that you don't want your players to be overwhelmed. But what if your players are kicking the crap out of the boss you've created for them? Fudging is even easier this way. Add a few dozen hit points to the enemy. Grant them a critical hit on a player character who's giving them a hard time. You could even have the enemy take on a greater form by adding another piece of armor, increasing their attack stats, or gaining access to a new spell. Whatever you do, it helps to have an in-game rationale for the change--not only does this rationalize the change, but it will enrich the story of the encounter.
So you see that developing an encounter on the fly is a relatively easy thing to do if you strip away all the math. You can give your players a memorable combat scene before returning to your regularly scheduled adventuring, and all without having to get involved in rules-heavy reading.
Coming soon: how and when to fudge rolls, how to deal with player issues as a GM, and a one-shot based on the movie Con Air. Until next time, happy gaming!
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