An encounter is any event that presents the PCs with a specific problem that they must solve. Most encounters involve combat with monsters or hostile NPCs, but there are many other types: a corridor full of robotic traps, a fraught negotiation with government authorities, an environmental hazard on a strange planet, an encrypted database that needs to be hacked, or anything else that adds drama to the game. Some encounters involve puzzles, interpersonal interactions, physical feats, or other tasks that can be overcome entirely with roleplaying and skill checks, but the most common encounters are also the most complex to build—combat encounters.
When designing a combat encounter, decide what level of challenge you want your PCs to face and follow the steps below.
Step 1: Determine APL
The first thing you need to do is determine your players’ Average Party Level (APL), which represents how much of a challenge the group can handle. To get this number, add up the levels of all characters in the party, divide the sum by the number of party members, then round to the nearest whole number (this is an exception to the usual “round down” rule). If the group contains fewer than four characters, subtract 1 from the result; if the group contains six or more characters, add 1 to the total. For example, if a group has six characters, two at 4th level and four at 5th level, its APL is 6 (28 total levels divided by six characters equals 5 after rounding up, and 1 is added for having six characters).
Step 2: Determine CR
Challenge Rating (CR) is a convenient number used to indicate the relative danger presented by an enemy, trap, hazard, or other encounter; the higher the CR, the more dangerous the encounter. Refer to Table 11–1: Encounter Difficulty to determine the Challenge Rating your group should face depending on the difficulty of the challenge you want and the group’s APL.
Step 3: Build the Encounter
Determine the total experience point (XP) award for the encounter by looking up its CR on Table: Experience Point Awards. This gives you an “XP budget” for the encounter. Every creature, trap, and hazard is worth an amount of XP determined by its CR, as noted on the table. To build your encounter, simply add creatures, traps, and hazards whose combined XP does not exceed the total XP budget for your encounter. It’s easiest to add the highest CR challenges first and then reach the total by including lesser challenges.
For example, let’s say you want your group of six 11th- level PCs (APL 12) to face a hard encounter on Eox against a crafty necrovite (CR 13) and some elephantine ellicoths (CR 9 each). Table 11–1: Encounter Difficulty indicates to you that a hard encounter for a group of APL 12 is equivalent to CR 14. According to Table: Experience Point Awards, a CR 14 encounter has an XP budget of 38,400 XP. At CR 13, the necrovite is worth 25,600 XP, leaving you with 12,800 XP to spend on ellicoths. Ellicoths are worth 6,400 XP apiece, so the encounter can support two ellicoths in its XP budget. Or you could skip the necrovite and use three ellicoths instead, leaving you with 19,200 XP to spend on other creatures or hazards (perhaps a CR 12 creature that shares the ellicoths’ lair).
Creating fun and balanced encounters is both an art and a science. Don’t be afraid to stray from the formulas by making changes— sometimes called ad hoc adjustments—that you think will make the encounter more fun or manageable for your particular party. In addition to the basic rules above, consider whether any of the following factors might apply to your encounter.
Creatures with abilities that match a class, such as creatures that belong to the PC races detailed in this book, function differently than creatures with substantial innate abilities. Their power comes more from gear than from nature, and they might have skills and abilities similar to those of PCs. Generally, the CR of an NPC equals the level of a PC with the same abilities—for example, an NPC with abilities similar to a 2nd-level technomancer would be CR 2. An NPC usually has armor and a weapon each with a level equal to its CR, give or take a level, and possibly one or two more items of a level equal to its CR. For more information on creating nonplayer characters, see the Alien Archive.
The sheer number of experience points involved in building high-CR encounters can seem daunting, especially when you’re trying to craft an encounter on the fly. When using a large number of identical creatures, Table 11–2: CR Equivalencies can simplify the math by combining them into one CR, making it easier to find their total XP value. For example, using this table, you can see that four CR 8 creatures (worth 4,800 XP each) are equivalent to one CR 12 creature (worth 19,200 XP). You can also use this table to work backward and build encounters with much less math. Need a CR 7 encounter using CR 4 creatures? Just check the table, and you’ll see that you need three CR 4 creatures to create a CR 7 encounter.
An encounter against a creature that’s out of its favored element (like an enormous dragon encountered in a tiny cave) gives the PCs an advantage. In such a situation, you should probably build the encounter as normal—you don’t want to accidentally overcompensate and kill your party—but when you award experience for the encounter, you may want to do so as if the encounter were 1 CR lower than its actual CR.
The reverse is also true, but only to an extent. Creature CRs are assigned with the assumption that a given creature is encountered in its favored terrain. Encountering a water-breathing kalo in an underwater area shouldn’t increase the XP you award for that encounter, even if none of the PCs breathe water. But if the terrain impacts the encounter significantly, you can increase the XP award as if the encounter’s CR were 1 higher. For example, an encounter against a creature with blindsight in an area with no natural light needs no CR adjustment, but an encounter against the same creature where any light brought into it is suppressed might be considered +1 CR.
As a general rule, the goal of ad hoc XP adjustments based on factors like terrain is not to penalize PCs for doing well, but to make sure they’re being challenged and rewarded appropriately.
You can significantly increase or decrease the power level of an NPC by adjusting its gear, particularly its weapons or crucial items such as powered armor. An NPC encountered with no gear should have its CR reduced by 1 (provided that the loss of gear actually hampers it). An NPC with better gear than normal—such as a weapon with 2 levels higher than the NPC’s CR or a large number of items with a level equal to its CR—has a CR of 1 higher than normal. This equipment impacts your treasure budget, so make overgeared NPCs like this with caution!
Just as a player slowly learns how to use his character’s abilities, so does a GM learn how to best deploy her collection of foes. CR can’t cover every situation, so a GM should think through both a creature’s abilities and the encounter’s setting for any potential pitfalls.
One major concern is the CR of the enemy. The CR system works best when the CR of each of the GM’s creatures is relatively close to the PCs’ Average Party Level. It might be tempting to throw a single higher-CR creature against the party, and sometimes that works out fine, but you may run the risk of obliterating the party when their saving throws aren’t yet high enough to protect against the creature’s abilities. Conversely, if you throw a horde of CR 1 creatures against your party with an APL of 8, those creatures are unlikely to hit the characters’ Armor Classes or succeed with any of their abilities, and thus they won’t be challenging, no matter how many you include.
Yet just as a tidal wave of low-CR enemies can become a tensionless slog for players, fighting a single opponent can also be a bore, depending on that opponent’s abilities. A lone technomancer without any bodyguards or defenses in place might find himself quickly surrounded or unable to cast his spells after being grappled, and a creature with a single powerful attack might still not be a great match for a party of five slightly less powerful characters due to the sheer number of attacks they have each round. In general, the strongest encounters have a handful of enemies that guard vulnerable creatures with powerful abilities and balance out the PCs’ number of actions each round.
|Easy||APL - 1|
|Challenging||APL + 1|
|Hard||APL + 2|
|Epic||APL + 3|
|Number of Creatures||CR Equivalency|
|2 creatures||CR + 2|
|3 creatures||CR + 3|
|4 creatures||CR + 4|
|6 creatures||CR + 5|
|8 creatures||CR + 6|
|12 creatures||CR + 7|
|16 creatures||CR + 8|
|CR||Total XP||Individual XP (By No. of Players)|