DM Guide: Setting Up An Encounter

No house rules or things necessary for play live here, just additional helpful reference materials. Basically think of this section as a bonus sourcebook.

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DM Guide: Setting Up An Encounter

Postby Lifeinwinter » Mon Jul 11, 2011 5:05 pm

Written by Ian in the PDM Forum, I'm putting this here on a more public forum for people who are interested in how to set things up for their first trial of running a scene.

Setting Up an Encounter, The Nuts and Bolts
Ah, the best part of the game, at least according to some: when you get to stab other people in the face and take their stuff. Even the most socially-oriented adventures eventually involve combat of some sort, and in most cases your goal as a DM is going to be to present a combat that presents a specific level of challenge to the party, while both being fun and (usually) advancing the plot. But while the amount of challenge you want to present will vary, successfully matching the combat to your desired difficulty is the most important part of any fight, and will depend on knowing a few things about how the game works.

Challenge Rating and Encounter Level
Most of you know at least vaguely the concept of Challenge Rating (CR)--a gauge of how nasty a given creature, trap, etc. is--and that every creature has one. What does it mean, however, to say that a creature has CR 4, 6, or whatever?

The concept of CR is pretty simple: given a party of average level X, a monster of CR X should lose to that party while forcing it to expend a fifth of its resources (hit points, spells, magic item uses, etc.). CRs usually assume that a party has ready access to the resources necessary to fight a particular battle (CR 6+ assumes that one or more PCs have access to flight, CR 4+ assumes that at least the party's fighter has a magic weapon, and so on). Yes, this means that a creature with a CR equal to a full party's level is not expected to be an "even match"--the PCs are outright expected to win any such encounter by breaking just a moderate sweat, unless they've already fought three or four times that day.

Where CR is expected to be an even match, at least in aggregate, is one-on-one. A 4th-level PC, for example, is expected to win against roughly half of the CR 4 challenges he faces on his own, and outright lose (die) against the other half. Note that this doesn't mean he's expected to be 50/50 against all CR 4 challenges: A 4th-level rogue will get whooped 1-on-1 by an EL 4 undead or ooze, will easily deal with a CR 4 trap or minotaur, and will probably go 50/50 with a barghest or sea hag, but overall he'll break even when run through the full CR 4 menagerie from the Monster Manual.

Encounter Level (EL) is based on the same principle, but it encompasses an entire encounter, whether it be with one enemy or several, and considers any mitigating circumstances. For a straight-up encounter with one creature, it's equal to that creature's CR (so a single CR 5 troll is an EL 5 encounter).

For multiple creatures, EL is a simple formula: every time the number of creatures at CR X doubles, the EL is X+2 (so two of the CR 5 trolls are an EL 7 encounter, four are EL 9, and so on). You can adjust more finely by using the midpoint of each range; in the above example, three trolls are EL 8, and six are EL 10. You can also mix-and-match: Two trolls and a Huge monstrous scorpion are also EL 9 (the two trolls make EL 7, plus the scorpion's CR 7 make EL 9).

Note: Once you have more than a dozen enemies or so, this formula becomes irrelevant. Thirty-two CR 1/2 goblins make an EL 9 encounter, but no 9th-level PC gives a crap.

Degree of Difficulty
As a rule of thumb, EL should not deviate from the party's level by more than +/- 3. Anything below that and you're better off just having the party roleplay some sword-swings before moving on. Anything higher says "I want a TPK tonight."

(The math bears this last point out: an EL 4 points above the party's level is equal to each member of a four-man party having an equal level opponent--which means the odds of a TPK are right at 50/50. For an EL of 5 or higher, a TPK is statistically the most likely result.)

Some basic guidelines:
  • For a mook-fight, where the enemies aren't meant to be more than speed bumps or plot-sparks, an EL equal to party level -1 or -2 is a good choice.
  • For an average "setup" fight, or one not meant to be particularly dangerous but making the PCs sweat a bit, an EL equal to party level or party level +1 is fine.
  • For a climactic battle in a multi-session scene where you've had some time for dramatic buildup and want a good payoff, an EL equal to party level +2 or +3 is sound.

Party Level
Contrary to what you might think, party level is not always equal to the party members' average level! The CR and EL systems are based on the assumption that there are exactly four PCs, so more or less can alter that balance.

For each character greater or fewer than four, add or subtract 1 from the average to get the party level. (Do not include familiars or companions.) For example, a party with PCs of levels 4, 5, 5, 5, and 6 is considered 6th-level overall (average 5, +1 for the extra member). A 9th-level PC running solo also has a party level of 6.

This is just an approximation of how to figure in that extra weight. It doesn't hold up well for parties that are very large (eight or more) or that have a wide level range (i.e., one or more PCs several levels higher or lower than the true average), but it's close enough for most purposes and keeps you all from needing calculus to figure this stuff. If you do have a widely-varied party in terms of level, use some extra caution; it's very easy for the outlier to either bulldoze an adventure (if too high and not restraining himself) or get smashed trying to keep up (if too low).

Basic Encounter Types
Typically, you're going to be looking at setting up encounters with either lots of little mooks (horde), a few well-balanced bad guys (squad), or one major bad guy (BBEG, or Big Bad Evil Guys). Even though you can set each of these three encounter types to the same EL, they will tend to have vastly differing results depending on how they're used! To wit:

Hordes are generally easy pickings; the PCs so far outclass their opponents that they are killing multiple creatures each round, and in a straight-on fight these are what you use to make PCs feel good about themselves. Unrelenting waves of foes can gradually wear down a party, however, and circumstances can conspire to make hordes nastier than normal. (The end of the movie 300 is a great example.) When using these, it behooves the DM not to get too hung up on numbers; you want them to maybe do a little damage, then go down quickly, and you can afford to fudge the numbers a bit to keep things moving.

If you want such a fight to be truly dangerous without being tedious, focus on "glass cannon" monsters--creatures with powerful attacks but surprisingly low ACs or HP counts--and/or reduce the bad guys' Con scores. Monsters should thus go down fast, but hit hard while they're up.

BBEGs, when solo, look nastier than they are. Sure, a Cleric 10 looks bad to a 6th-level party...but the Cleric can only cast one spell per round, and quickly falls behind the party in sheer numbers of actions. Single-BBEG fights tend to be hit-or-miss--decided very quickly, for good or ill, in exactly the sort of battle you want to be a drawn-out climax. Mitigating factors can alter this balance, however, such as access to Quickened spells or means of calling minions without changing the EL (such as summons), but generally solo fights are hard to handle while preserving the dramatic weight you want the fight to have.

Squads are usually the nastiest sort of encounter. They can match a PC party for number of actions, and when using sentient foes, they can pit the PCs' own tactics against them (they have not only the ability, but usually the Intelligence for it). A well-rounded, level-appropriate NPC party (a.k.a. the Mirror Party: equal in number to the PCs, with each NPC 1-2 levels under their PC equivalents and each traditional party role filled) is absolutely more fearsome than any single monster you can come up with at the same EL.

Mix and Match
You can blur the lines between these party types to good effect. For example, a climactic battle for a major, multi-scene adventure might involve the BBEG (at party level +1), along with a couple of lieutenants (each at party level -1). This produces an EL of party's level +3 (as high as you'd want to go), gives the enemies multiple actions per round so there's no gang-stabbing (and allows them to utilize teamwork tactics), but still gives the PCs an advantage in numbers that they can take advantage of.

Some Additional Notes
The following are extra things to keep in mind when determining the likely difficulty of your encounter...

The [Awesome] Subtype
Certain creatures actually have a higher CR than the books say they do. This, by all accounts, is on purpose (though no one's ever figured out why), and has been referred to as "the Awesome subtype." Most iconic creatures (dragons, mind flayers, beholders, demons/devils, etc.) have this "subtype." Basically, whenever using these creatures, mentally add a point to their CR. For dragons in particular, add an additional point (bringing their CR to +2 above "book value") if the PCs are not prepared for the encounter when it appears (such as with the appropriate energy spells/protections).

Circumstantial Adjustments
Encounters can be easier or harder depending on how they are sprung, and the book-listed CR/EL system presumes that both sides are equal in abstract—that is, that neither side is surprised, and that the terrain and other circumstances pose no distinct advantage to either side. If one side or the other has a distinct tactical advantage going into the encounter, you should consider adjusting the EL by a point or two as appropriate.

Examples might include fights in the dark against creatures with darkvision, fights against swarms without having any area-of-effect items handy, fights against flying creatures with few ranged weapons, fights against enchanters or fey with all fighters, or fights against undead with a preponderance of rogues and no cleric. This cuts both for and against the party: A 2nd-level party with horses and bows in the open plains can actually slaughter a CR 7 monstrous scorpion without breaking a sweat, and that barely even counts as an encounter, while even an 8th-level party trapped in a 20x20 room with that scorpion is in for some pain.

Along the same lines, the system tends to presume that creatures are using tactics appropriate to their intelligence. Demons and devils, for instance, are presumed to be using complex tactics and spell-likes or other powers as befitting their high Intelligence, while animals are presumed to be limited to "fight-or-flight."

This can be hard to look at objectively (no one wants to think they're playing a creature "too dumb" by accident), but in all honesty, playing a creature in a way not befitting its intelligence can be worth an adjustment to the EL. I see this a lot with dragons; when used as a big lizard with claws and a bite, you might as well be using a wyvern without the stinger. But when played to type, with full command of their abilities, they're worth every bit of that Awesome subtype I mentioned.

More on Difficulty, or Your Threats Shouldn't Always Be Dire!
Because combat is so slow here, we often use less of it in an adventure than a standard tabletop would use. As such, I've seen that many fights are weighted towards the high end of the difficulty spectrum, as DMs and PDMs try to get the most "bang for their buck." (If you only want to take the time for one fight, you're going to leap straight to the climactic one without the gradual lead-in that most TTs provide.) This not only comes as a shock to many players, but constant mortal peril loses its effectiveness after a while—there's nothing special about climactic battles if every battle is a climactic one.

I'd encourage people running longer adventures to avoid this reliance on the money-shot fight. PCs don't have to be in obvious mortal peril every time they roll Initiative, and giving the PCs a chance to beat down some mooks to advance the plot, or gradually ratchet up the tension with increasing difficulty, can be fun for everyone involved. (Just keep tabs on your players' moods and avoid tedium—when they get bored with mooks, it's time for the rest to flee or fall down so the plot can advance.) This lends extra weight to the fights that really matter, both in your adventure and beyond.

Note that this is easier when you are familiar with the combat rules, as well as when you're willing to do some improvisation. For instance, if you're running a mook-fight and a rules question arises, or someone tries to do something flashy that isn't necessarily legal, call it in favor of the PC for the moment and move on--then look it up later for clarity's sake. The PCs are meant to win these sorts of fights anyway, so delaying the inevitable to look stuff up is silly.

Stick to What You Know
Some monsters look really cool, but they require the use of tactics, spells, or abilities that you're not as familiar with. (Swallow whole, anyone). Some players play more at high levels than low, or vice versa, and simply aren't accustomed to what options are available at certain levels. Using unfamiliar monsters does more than just slow down the game as you look up references—it can also affect the difficulty of your encounter, either through incorrect use or simply not using the unfamiliar powers at all.

When possible, use creatures with abilities you're comfortable with. If you've never had to deal with the improved grab rules before, the right time to figure them out is not when a tendriculos is trying to devour a PC in the climactic battle. If you must use these sorts of things for the sake of your plot, grab a DM (or really knowledgeable player not in your scene) beforehand and see if they'd be willing to run through a quick practice fight. That way, you can see the abilities in action and figure out how they work before you grind play to a halt when it really counts. (Oh, and if you get a player to do this, be nice and nominate them for some extra XP, too.)

I Don't Want the PCs to Fight!
In some cases, you'll want to present the PCs with an encounter they "obviously" want to avoid in order to drive the plot in a certain direction (you want them to use stealth, guile, cunning, or diplomacy, for instance, or you want them to go get a MacGuffin first). This is risky for several reasons, including:

1. You run the risk of appearing to railroad your players. While the basis of DMing in the first place is to nudge players in a given direction, like with many other things you have to use a deft touch to make it work.

2. You run the risk of your players not getting the hint and biting off more than they can chew. This results in very dead PCs and players who probably think they got shafted--and depending on how it happened, they might even be right.

Here are a few notes on avoiding the pitfalls mentioned above:

1. Make good use of description! This is a good storytelling trait to cultivate in general, but this sort of situation is where it shines. Without telling the players what they feel, describe the truly imposing nature of their potential adversary, perhaps allowing them to make Sense Motive checks to discern how rough a task lies ahead.

(See Complete Adventurer for info on using Sense Motive to gauge an enemy threat. But freely ignore the part where it wants you to spend a standard action on doing so.)

Through vivid description, you can convey a sense of "You don't wanna go there" without outright saying "You don't wanna go there." Just make sure your hints aren't too subtle—one person's subtle is another's "simply not there," which leads to #2 above.

2. Make sure the alternatives are clearly visible, and try to allow for more than one. You may have to be a bit obvious in this regard; no one likes handing the keys to an adventure on a platter (nor do PCs enjoy simply being handed those keys), but as I mentioned, sometimes you can think you've made something clear only for otherwise-perfectly-astute PCs to miss it entirely. And if the PCs feel they have no other options, they may do precisely what you don't want them to do. (Many PCs tend to have a mindset that says, "The DM won't throw anything truly unbeatable at me," which leads them to pick fight over flight when they shouldn't).

Again, try to present options beyond fight-or-flight. Even players that will sometimes think in terms of flight don't prefer it, because running away (especially if it's meant to go get beefier characters to fight for them) negates player agency and isn't fun. So if PCs can't hope to prevail in your straight-up fight, try to give them more options to get around it and advance the plot; stealth, diplomacy, intimidation, and others not only allow for this, but also give PCs that aren't combat-machines a chance to shine.

3. Use some caution with ambushes or bait-and-switch tactics. Encounters that look like mook-fights but are actually hardcore battles are tricky if not handled carefully, and can make players extremely upset if they turn bad. For example, the frail-looking old man who suddenly turns out to be a balor in disguise can go badly fast unless you work in some hints beforehand (or a balor is actually an appropriate-CR encounter for your party).

4. If all else fails, be sure to plan for the possibility that the PCs will do the unexpected. (Again, another good DMing trait to cultivate in general.) If you've given PCs plenty of IC hints on an encounter far beyond them, you can always let the dice fall where they may.

Crap, I Misjudged And All The PCs Are About To Die
Crap happens sometimes. Dice go on a run of suck, hints aren't seen or taken, DMs misjudge what their players can handle, PCs make bad choices, and despite the best efforts of everyone involved, your story is suddenly about to end with "Swords fell and everyone died." Bummer. Death happens, but a TPK sucks the fun out of things for everyone. You can avoid this, though!

The first key is to be aware of how the fight is going, and keep tabs on what resources are still on the table. If a couple PCs are down but the cleric's still up, the bad guys are hurting, and the sorcerer still has six disintegrates, let it ride. If the cleric goes down, no one has spells or powers left, and the bad guys are still in good shape, it's probably time to intervene.

How do you do so without it being obvious? Having bad guys suddenly put the kid gloves on, or having NPCs ride to the rescue, is an agency-robbing deus ex machina that leaves PCs feeling cheated and can break immersion in your story. Rather, if you're planning a high-end encounter where this situation is a risk, you should include a conditional "out" for the PCs as part of your setup. Some examples:

  • The bad guys want to question PCs later, sacrifice them to their dark gods, etc. If half the party is dead, they purposefully seek to stabilize dying PCs and switch to subdual damage to imprison survivors, leading to the ever-popular jailbreak scenario.
  • In a sufficiently dire scenario, PCs can notice something about the environment that lets them turn circumstances to their advantage. They cause an avalanche that takes out or divides some of the bad guys, or just delays them long enough for the party to escape.
  • Give PCs a logical chance to escape, but the timing is such that they can't take the fallen with them. This feels like less of a deus ex machina because the PCs still suffer failure, and leads to further adventure--not only do the PCs still have bad guys to deal with, but now they have to recover the bodies of their friends, and they might have a time limit.
  • This might be a good time to give more upstanding PCs the chance to sacrifice for their colleagues. If a player's indicated this might be something they're into, offer them the chance with a Bluff check to goad attention onto themselves, or to lure the bad guys into a trap, so the others can escape or reach a more advantageous position. A PC still dies, possibly in a way they can't come back from, but they get a hardcore ending that everyone else will take back with them and tell stories about for years. Many players will leap at this.

Note: Combat can distract even the most clever players, so you might offer some Int rolls for those who fail to notice the method of their salvation when you provide it.

On the flip side, if the PCs actually win an encounter they shouldn't have fought in the first place, you can save some gnashing of teeth and tearing of hair by preparing for that possibility in advance. Give your villain the same sort of logical "out," or simply re-write your background and make him the subordinate of an even greater threat. Goose, gander, etc.
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