The Issues of CRs and Multiple Creatures in Starfinder
So if you look in the Starfinder Core Rulebook, it’ll tell you that encounter difficulty is determined by comparing an encounter’s CR to your player’s Average Party Level (APL), as follows:
|Easy||APL – 1|
|Challenging||APL + 1|
|Hard||APL + 2|
|Epic||APL + 3|
It’ll also tell you that you can determine the CR equivalence of multiple creatures with the following table.
|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|
Both these tables are useful… and both are wrong in ways the core rulebook doesn’t explain (we didn’t really realize it when we wrote the book — or at least I didn’t), and that isn’t intuitively obvious. But depending on how you combine these, your encounters may be way too easy, or way too hard.
Let’s start with when it may create an encounter much harder than expected.
Single Creatures of Higher CR
If you use a single higher-CR creature to make an encounter above your player’s APL, that encounter is going to be much harder than the core rulebook suggests. A single creature 1 CR higher than your PCs’ APL is on the tougher end of “Hard,” not merely “Challenging.” A single creature 2 CR’s above APL is Epic. And a single creature 3 CR above APL is likely to be more murderous than fun.
The reasons for this are baled into how Starfinder is different from pathfinder. First, the math is tighter. In Pathfinder you often have 1 or 2 players who are well ahead of the average PC curve in one area or another. Thus when you challenge them with a higher-CR foe, the one PC who is above the curve in whatever aspect of the game is effective against that foe can affect it, and the other PCs can support them. In Starfinder, the upper level of effectiveness is much more tightly controlled (and monster state blocks are much more consistent), so as the CR of a single monster goes up, the % chance of any attack of ability affecting them drops in ways the PCs cannot easily deal with.
Similarly, the raw bonuses and DCs a monster has increase in ways the PC’s defenses aren’t designed to handle, and a single higher-CR creature is likely to focus its attacks more than two lower-CR ones, just as a practical matter of space, reach, and line of sight.
Relatedly, the prevalence of save-or-lose effects is much lower in Starfinder than Pathfinder. In Pf, if you are just facing one foe players can spam hold or similar spells until the enemy fails a saving throw. Which such effects exist in Starfinder they are much less common, and generally more limited in scope.
Additionally Starfinder generally increases combat effectiveness not with multiple attacks, as Pathfinder does, but with each single attack anyone makes doing more and more damage. This both means the PCs can;t spam 3-6 attacks a round at a foe hoping to roll well on at least a few (and thus get a little damage in each round), and that a GM can’t have a foe divide their attacks among multiple PCs to make sure one is not killed in a lucky shot.
These factors combine to mean than one CR 8 foe is much more dangerous to a group of PCs than three CR 5 foes. It is much harder for the PCs to connect with it, given it’s higher ACs and better saves, and rather than have the threat be reduced as they drop one enemy and can focus on the other two, it remains at full effectiveness until dropped. And many legitimate class builds that focus on area attacks which help deal with three CR 5 creatures are actually less common against one CR 8.
So the table that tells you an APL +3 encounter is Epic (but reasonable) is only true if you are using multiple creatures of roughly your parties APL.
But, of course, there’s another possible weird result, when things are much easier than expected…
Multiple Creatures of Lower CR
The other thing the core rulebook tells you is that 16 creatures make up an encounter with a CR equal to their indiviual CRs +8. That ought to mean that if you have an APL of 9th level, you can challenge them with 16 1st level foes.
But you can’t. I mean you can do it, but it won’t be a challenge.
In this case, the tighter math and reduced attacks per round work in the PCs’ favor. The AC of a typical CR 1 combatant is 11 lower than a CR 9 combatant, and it has 20 HP, compared to the CR 9’s 145. One or two area attacks can wipe out all the CR 1 foes, and their attacks are insignificant even if they manage to connect with PCs.
Now being able to be in multiple places can given useful otpions, and of course a clever Gm CAN build an encounter where eight CR 1 foes are at least interesting (putting them in defensive positions, for example, or spread them out and set the encounter so the PCs want to capture them all without letting any escape, rather than just defeat or bypass them). But failing that, for a satisfying encounter you generally don’t want to use foes with a CR more than 3 below your PCs’ APL.
When using the CR system in Starfinder, try to stick to creatures with a CR no more than 3 below, or 1 above, your party’s APL.
(Unless you are prepared to get clever, as I experimented with when building a CR “6 +1” Manticore.)
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