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GameMastery Guide / Running a Game / How to Run a Game / The Science of GMing

Building Encounters

Source GameMastery Guide pg. 40
One of the ironies of being a GM is that it’s not your job to create a fair fight between the PCs and monsters—if it were a fair fight, the PCs would lose half the time, and that makes for a very short adventuring career. Consider a “fair” fight between four 6th-level PCs and four 6th-level NPCs; the NPCs are a CR 9 encounter, which has a good chance of killing one of the PCs, but the PCs are likely to kill all the NPCs. This is how it should be—your job is to create encounters that are challenging, which means the PCs are expected to win, but should have to work for it. The following section gives advice on building encounters that are challenging, memorable, effective, and interesting.

Play to the PCs' Strengths

Source GameMastery Guide pg. 40
As a GM, you should know your players and their PCs, and create encounters that suit their play style and show off what their characters can do. If the fighter’s player likes to jump into the middle of groups of monsters and hack away, be sure to include such encounters every so often so that player gets to do what he likes best. If he has the Cleave feat, set up situations where he can cleave an adjacent foe; if he has Great Cleave, make sure every now and then he can go cleave-crazy on a horde of weak opponents. If the sorcerer’s player is a tactician and likes to use ranged spells and enchantments, put her against charm-vulnerable opponents using ranged attacks so she has perfect targets for her style of play. If the monk’s player is a fan of Wuxia films and likes the extreme-cinematic style of combat, put opponents on ledges so he can use high jump, or enemies at the bottoms of cliffs so he can get there quickly using slow fall, and make sure some enemies aren’t immune to stunning fist.

This means you should keep an eye on what feats and spells your players select as their PCs level up, and on what magic items you award them or they create. If the fighter takes Great Cleave at level 5 and only gets to use it once by the time he’s reached level 10, it’s as if he wasted that feat choice, and that’s not fun. You want the players to use the abilities that make them excited about the game. Reward them for playing well by letting their characters flex their muscles.

This is not to say that you shouldn’t challenge the players to try different tactics. Put the fighter who likes being surrounded in a situation where he has to guard a narrow bridge and can’t let anyone get past him, or have him fight monsters that get flanking bonuses or sneak attacks that make him rely on terrain or the other PCs to avoid getting killed. Let the tactician-sorcerer take control of a minion. The trick is to teach other styles of play (or at least present them as options) without them feeling forced.

High- and Low-CR Encounters

Source GameMastery Guide pg. 41
The game expects that for about half of the encounters the PCs face, the CR of the encounter is equal to the average party level (APL). Obviously the rest of the encounters are higher or lower than the average party level, but what is too low or too high?

Table 12–1: Encounter Design only covers encounters from APL –1 to APL +3, so that CR range is the usual limit for most encounters. After all, for a party of four 6th-level PCs, an “easy” encounter (APL –1) is a “rival” group of four 2ndlevel NPCs (CR 1 each, +4 for 4 creatures = CR 5); if beating up NPCs one-third your level is easy, beating up even weaker creatures is more like bullying than adventuring. The risk of using very easy encounters is that the players may grow bored—they know their characters can deal with the monsters, but have to go through the motions of making attack and damage rolls without the excitement or risk from a “real” encounter. (Much like a “god mode” setting in a video game, the novelty of easily destroying all opponents gets old after a few encounters.) In some cases it’s acceptable or even a good idea to lead off an adventure with a very easy encounter—for example, if the players need a morale boost or have power-boosting abilities that require some kills to start functioning—but in most cases you don’t want to create encounters below APL –1.

The value of APL +3 should be a fairly hard limit for difficult encounters unless you want there to be a considerable risk of PC death. Once you’re beyond APL +3, the PCs’ ability to pose a threat to a monster dwindles, especially if the encounter is a single powerful creature rather than multiple ones on par with the APL. In most cases, this is because using a higher-CR monster may cross one of the invisible “break points” in monster design where the creature’s defenses and abilities assume the PCs are a certain level and have access to certain spells or gear, such as magic weapons, spells to remove ability damage, items neutralizing poisons or disease, or even simple things like being able to hit the monster’s AC or meet its saving throw DCs. If the PCs lack a critical spell or piece of gear, a difficult encounter may be nearly impossible.

For example, a succubus is a CR 7 encounter, and is an “epic” encounter for a group of four 4th-level PCs. Most PCs at that level lack cold iron or good weapons, and thus have to deal with the demon’s DR for every attack. The PCs may have difficulty overcoming her SR 18, energy resistances, and immunities, thus spellcasters will be frustrated. The PCs have even odds at best of resisting her at-will charm monster and suggestion (usually taking one PC out of the fight), and have to work very hard to make up for the temporary hit points from her at-will 6d6 vampiric touch.

It’s entirely possible to have an exciting and challenging fight (CR equal to APL +1 or +2) without overwhelming the PCs. An “epic” fight may last two or three hours of real time—a memorable fight if the PCs win, but a depressing slog if they can’t. It’s generally better to keep combat encounters to about an hour—that way you can get two or three encounters into one night of gaming, and make more progress in the adventure or campaign than a single, longer fight. If the fight you’ve given the PCs ends up too tough for them, don’t forget to remind them that they can run away, or you can cheat a little bit and suddenly treat the monster as if it had the young creature template (–2 on all rolls), which might be enough to turn the tide in the PCs’ favor—after all, you want the PCs to win, because that means everyone gets to keep playing. Killing them with an accidentally-too-hard encounter is no fun for anyone.

Solo Monsters vs. Groups of Monsters

Source GameMastery Guide pg. 41
Sometimes there’s the temptation to use one powerful monster instead of multiple weaker monsters. The main drawback to this encounter-designing tactic is that the PCs outnumber the monster; even in the optimal situation where the monster attacks first, a group of four PCs gets to attack four times before the monster gets another turn, and with good planning it’s entirely possible for the PCs to kill the monster in one round. Using multiple monsters forces the PCs to either focus their attention on one opponent (giving the remaining opponents more opportunities to attack) or engage all of the opponents (preventing an immediate slaughter). Using multiple monsters also lets you set up special abilities like sneak attack that are difficult to implement with a single monster, and means you can distribute the monsters’ actions throughout the round (whether by rolling separate initiatives or using the delay or ready actions) and react more than once per round to what the PCs do.

Remember that, as a GM, you have tricks up your sleeve, and if the PCs are having an easy time dealing with a solitary monster, it’s all right to send in reinforcements. An intelligent NPC may have bodyguards en route. A brutish monster may have a handler or trainer within earshot of its cries for help. Even an unintelligent creature like an ooze or big zombie may benefit from the arrival of wandering monsters.

Winning Monster Combos

Source GameMastery Guide pg. 42
Some monsters are best used in groups or with other creatures that complement or augment their abilities. A single derro probably has a hard time using its sneak attack, but a group of them can easily set up flanking situations. Tieflings have fire resistance 5, making them handy allies for a fire priest with burning hands or a fire mephit; alternatively, a tiefling cleric controlling a gang of burning skeletons is all but immune to their area damage. Creatures with spell-like abilities can cast them on minions or on a leader. For example, a dark naga or spirit naga can cast cat’s grace, invisibility, or displacement on its allies; a spirit naga can even turn itself invisible and cast cure spells on its allies. Given time, a succubus’s profane gift ability can bolster every single guard, priest, and lieutenant in an evil fortress.

Monster abilities can also complement hazards or traps; a flying monster ignores difficult terrain, floor pits, or patches of green slime. Monsters with damage reduction are immune to arrow traps and most spear traps; those immune to poison can ignore the danger of poisonous traps or even rooms with inherently toxic air, such as a sulfurous volcanic vent. Using monsters intelligently like this helps create fun and memorable encounters, as well as challenges PCs to try new tactics.

Don't Stymie the PCs

Source GameMastery Guide pg. 42
This is another way of saying “play to the PCs’ strengths,” but is worth reiterating. Part of the fun of playing is leveling a character and gaining new abilities. If you create encounters that circumvent the PCs’ newest abilities, it takes away some of the fun of the game because it’s like they didn’t gain all the benefits of their level. For example, if the PC wizard just reached level 5 and learned the fireball spell, you may be tempted to throw some fire-resistant or fire-immune encounters at the PCs to compensate for this ability—which makes the 5th-level wizard feel like a 4th-level wizard. However, thousands of RPG campaigns have survived PCs who can cast fireball; it’s better for a GM to embrace the new ability than fear it. Give the wizard a cluster of minions to blast so he feels powerful—or set up an encounter where he has to choose between blasting a bunch of minions or using the spell on just the boss.

Some monsters are designed to be more challenging to certain character classes. Golems are immune to almost all magic, some outsiders have very high damage reduction, oozes are immune to critical hits and sneak attacks, and so on. If the PCs end up facing these kinds of creatures over and over again (especially in a short amount of time), the stymied players can easily get frustrated—after the third encounter with stone golems, the sorcerer and wizard are likely to give up and want to stop playing. If you’re going to use a lot of these creatures (say, in a themed dungeon), you have two options to prevent player frustration.

Give the Character a Tool: There are dozens of limited-use items in the game, plus consumables like potions and scrolls. If you know one PC is going to have a problem with an upcoming encounter, drop a helpful item into an earlier encounter or even an earlier adventure—an item that lets the character be useful in the battle despite the monster’s resistances. If a PC druid has no magic weapons and you’re planning an iron golem encounter, give her a golembane scarab so she can better attack it in wild shape. If a PC rogue has no bludgeoning weapons to use against a black pudding, let her find a low-level wand of magic missile and blast away using Use Magic Device. Many items and spells in the game are designed to deal with unusual encounters, but don’t see play very much because PCs prefer general-utility magic; introducing a cheap or expendable item like this gives smart players something to fall back on if their primary strategy isn’t effective or if they run into an encounter where the unusual tool is exactly what they need.

Present Other Options: Just because the encounter involves a monster doesn’t mean that all the PCs have to focus on defeating that monster. Create another task that helps overcome the monster, prepares for the next encounter, or disables a parallel threat during the fight. For example, in a fight against a bunch of black puddings, rather than having the rogue frustrated by not being able to use sneak attack, add a spiked wall trap that the rogue can disable while the other characters deal with the oozes. If the encounter has an iron golem and the wizard has no electricity attacks to slow it, put a magical puzzle-crystal in the room that unlocks a secret room if the wizard makes a Knowledge (arcana) check. If the party cleric channels negative energy and the other PCs are fighting undead (meaning the cleric would heal enemies if she tried to channel), include a door made of fused bone that only opens from a focused blast of negative energy. If the opponent is resistant to physical attacks, put a chained prisoner in the room that the barbarian, fighter, or paladin can rescue while the spellcasters deal with the threat.