9 Ways to Balance Encounters
These are some of my own personal guidelines to planning just the right encounters for my games.
#1 Never put balance first.
Sure, sometimes you want a balanced encounter. Or at least to know which side in an encounter is favored and by how much. Sometimes it's desirable to design an encounter within a certain range of difficulty. Fair enough. The pitfall to watch out for--one that's rarely given any consideration--is the rules-first attitude where the story and/or genuine portrayal of the game world become secondary. When you think in terms of "What monster can I put here to deplete 20% of the party's resources?" rather than in terms of "What monster can I put here that will really make the adventure pop?" the game suffers. If the ideal encounter story-wise is too tough mechanically, you can always write in extra resources, benefits, or advantages to help the party. Likewise, if it's too easy, you can always adjust by including special constraints or conditions to challenge the party.
#2 Identify the purpose the encounter serves.
This doesn't only apply to linear story adventures. Even random encounters in a sandbox style campaign serve some purpose, whether it's to provide a challenge, keep the party from dawdling, or to help illustrate what the environment is like. Contrary to how it is typically portrayed, balance is not a linear continuum. The exact purpose of the encounter affects which factors are relevant to balancing the encounter.
#3 If the PCs are supposed to run from this thing, you better make sure they actually can escape it.
Being mindful of size, maneuverability, and of course speed can be more relevant that combat statistics. Though it probably also helps if it's clearly more powerful than the PCs. Not just slightly more powerful. It should be an obvious TPK. Otherwise the PCs might decide to fight it thinking they can win and find out all too late that they're wrong. Whatever mathematical scale you ultimately use to evaluate relative strength, the monsters should be about four times as powerful as the PCs.
#4 Choose your battles.
If it's a fight, you need to know what kind of a fight. I generally use four main categories of combat; the mook fight, the guardian fight, the road fight, and the boss fight. Boss fights and guardian fights need to be planned more carefully than the others and will be discussed below in further detail. Mook fights should be of a difficulty rating so low they provide no real challenge and pose no real threat to the party. Of course, nothing is safe from random chance. Road fights, on the other hand, can vary wildly in difficulty. They generally punctuate the adventure and setting. Random encounters generally fit under this heading. Players will have to figure out for themselves how to best deal with them... or avoid them.
#5 Know your boundaries.
The first of two types of guardian fights are boundary guardians. The purpose of these encounters is to keep the party out of areas where they should not be. This is generally for their own good--they may not be ready for what lies beyond. It might also prevent the party going "off the map" or from taking a shortcut that would otherwise lessen the adventure. They can also guard areas you just haven't prepared yet but are reserving for future adventures. As such, boundary guardians should be effective at keeping the players from passing. They need not be more powerful than the party per se. But the risk-to-reward of fighting them should serve as a deterrent. Some of the most effective boundary guardians have invulnerabilities the party just can't overcome yet, such as only being hurt by magical weapons, or are very strong but with vulnerabilities that the party is not yet able to exploit.
#6 Gateways to adventure.
The second type of guardian fight are gateway guardians. They serve a simple purpose. This is the reason why everyone and their mother can't take up this adventure. They should be formidable enough to keep ordinary people out. At the same time, because they mark the start of the adventure, you usually won't want them to deplete the party too much. It can be helpful if the party has some unique or rare combination of abilities or special information that enable them to defeat the guardians.
#7 The big battle.
Typically the centerpiece to the adventure, the big battle is perhaps where balancing the encounter is most important. You have to be able to anticipate the condition the party will be in at this point in the quest--they may not be at full strength. Whatever the case, an even match is often ideal. This guarantees the PCs will always have a fair chance at winning, always stand a real chance of failure, and always risk the possibility of loss. While I generally plan these to scale to some degree to the size and power level of the PC party, a portion of their power is also fixed. This allows the choice of the players to take on the level of risks with which they are most comfortable.
As the centerpiece to the adventure, more important than balance is that the fight is interesting. Mixed groups work best with a few leader types (total number ranging from 1/2 to equal the number of PCs) with the main leader slightly more powerful than the most powerful party member, and the lieutenants slightly less powerful than the average party member. Use mooks to raise the difficulty of the encounter to the desired level.
#8 By the numbers.
The RPG you're playing may already have a system for comparing power levels of characters and monsters. If not (or even if so) you may measure things as follows: For each side, determine the average probability of hitting, average damage, average number of attacks, and average hit points. Multiply the percent change of hitting by the average damage and by the average number of attacks. This is the expected damage per round.
Trace through the effects of both sides, round-by-round, remembering to reduce the damage each size does proportionately when the accumulated damage is sufficient to kill a party member.
Based on these numbers, it will take the party, at full strength, about 5 rounds to slay Cerberus. At full strength, Cerberus can kill the entire party in 4 rounds. However, if any one of Cerberus' heads are disabled, it loses the ability of collective gaze, thereby losing about one third of its offensive power, meaning it will take 6 rounds for it to slay the party. Also, if its middle head is disabled, it loses its poison spittle power, nullifying another one-third of its offensive force, meaning it could take as much as 12 rounds to slay the party.
It is possible for the party (in the best case scenario for the party) to take out the middle head in one round, thereby disabling both powers. As Cerberus would have already done one round worth of damage by then, it will take 10 rounds total to destroy the party. The party, weakened after Cerberus' first round assault, will deal only about 35 damage per round on average after the first, meaning it will take another 6 rounds. If Cerberus can continue to slay a party member every other round after the first, however, he will live longer than the 6 rounds, and it could be anybody's fight. Based on this quick and dirty analysis, a party that intelligently targets Cerberus is an even match. A less strategic one, however, will likely be unable to defeat the three-headed hound of Hades.
Although highly nuanced and somewhat math intense, this is the most accurate way to anticipate the outcome of a battle as the battle with Cerberus generates, for this particular example included a lot of special cases. In more ordinary fights, a simple ratio from the given statistics may be drawn. If we assume hit points to be proportional to how long a character or group will survive, simply multiply damage per round for each side by their own hit points. Divide the monsters total by the PCs to get the Challenge Quotient (CQ).
#9 Bringing it all together.
We talked about encounters the party is meant to run from, mooks, two types of guardians, road fights, and bosses. The Challenge Quotients of the various encounter types are as follows:
Mook Fights: 1/10 to 1/4
Gateway Guardians: 1/4 to 3/4
Road Fights: 1/4 to 3
Boss Fights: about 1*
Boundary Guardians: 3/4 to 2
Chase Encounters: 4 and up
* Give or take a quarter, or even a half point depending upon the skill of players, the NPC use of intelligent tactics, and the level of difficulty intended.
I hope this has been helpful. It should only be viewed as a quick-and-dirty guide rather than rigid rules to follow. Creativity trumps all, and these guides should only ever be considered after the main ideas for the adventure have been formed.
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