World Building: Weaving Plot Threads

A good story never has just one thing going on. To make the world feel alive and add depth to the characters you'll often find that two or more things are going on in parallel as a story progresses. You see this a lot in books, TV, and film where the action jumps between separate but related groups of characters and follows them for a short time while they do something important before the story's focus moves on to a different group. At certain points these threads intersect but it can be a long time in between and when they do it's usually because something important is happening.

In interactive storytelling this kind of narrative structure can be difficult to pull off. Your audience are active participants instead of spectators, so you can't have the action move away from them to go focus on another group unless you split the party. As any good GM knows you don't ever split the party lest a truly horrible fate befall your campaign. Instead of pulling the focus away to follow other characters, telling these secondary stories must be done more subtly. Players will likely never get the full story of what's going on outside of their view, but they can get windows into it through interactions with NPCs, active information gathering, and times when the action of another story thread intersects their own.

There's a great example of this in the movie Shaun of the Dead: The protagonist Shaun and his three friends are fleeing a zombie apocalypse on foot when they round the corner of a building and run into another survivor who is an acquaintance of Shaun's and three of her friends traveling in a different direction. They briefly tell eachother of their survival plans and then the other party go on their way. The story is told entirely from the point of view of Shaun and his party so we never see what happens to this other party before or after their brief encounter. You can't help but feel though that they're the heroes of another story running parallel to Shaun's and wonder what will happen to them. Events like this are spread liberally throughout the movie, often happening in the background as the action moves past them. They're never directly focused on but they give the viewer an impression that there are other forces at work, other events going on, and that the world does not revolve around the central characters.

A typical way to construct a story like this is to have two main plot threads, the "alpha plot" and the "beta plot" and a plethora of mostly-inconsequential background events that are loosely related to the two plots but serve primarily to add flavour and make the world seem larger. Additionally, these plot lines may tie into an larger storyline, often called an "arc". A very well layered story may have several arcs weaving their way through several episodic plots.

Alpha Plot - The Heroes' POV

This is the story your characters are in direct control of. The alpha plot is their story and most of the events that they participate in should contribute to advancing and steering this plotline. When planning a campaign this plot will have the greatest level of detail and have the most possible directions for the players to choose. If you're playing episodically, this plot starts at the beginning of an episode and the episode ends when this plot is concluded.

Beta Plot - The Under-current

This is the story happening just outside of the party's field of view. It's driven mostly by NPCs and the side-effects of events in the Alpha Plot. The party get glimpses of this plot from time to time at points where it intersects the Alpha Plot. Often NPCs that are important to the Alpha Plot will be important to the Beta Plot as well, and probably know more about it than the players. If your story has villains of the scheming type it's likely the beta plot will feature a gambit of some kind that only comes to the forefront late in the Alpha Plot.

Arcs

Most long-running episodic adventures will have story arcs. These are much longer running pieces of narrative that individual episodes' Alpha or Beta plot will relate to in some way. A highly episodic adventure may have one or more story arcs as the only thing linking individual episodes together. An adventure with longer episodes (or chapters) may have several arcs interacting within a single plot. For examples of different kinds of arcs, I'm going to use the movie Snatch (apparently I have a thing for British comedy).

Arcs: Character Arc

A character arc is simply how one individual grows and changes over time. A well-constructed character arc will spans several episodes and shows the audience how the events of those episodes have changed the character within the parameters of their persona. A character arc might follow a young, reckless warrior through a string of battles (episodes) where he learns restraint, honour, and strategy and grows into an accomplished tactician. A different kind of arc might follow a cunning and manipulative leader as she gains rapidly power, only to fall from greatness into madness as her scheming pushes away allies until she is left with nothing.

In Snatch virtually every character undergoes some sort of arc, but the best examples are Mickey (the Traveller boxer) and Avi (the American jeweler). Both of them start off just living their lives, get wrapped up in either the Boxing Match Alpha Plot or the Diamond Heist Beta Plot, and end up significantly burned out and arguably worse off than when they started.

Arcs: Item Arc

An item arc happens when an inanimate object of some importance passes through several people's posession and impacts the story of those around it in some way. The One Ring from The Lord of the Rings is probably the best-known example. Its arc passes through the story of the War of the Ring, the history of Gondor, and The Hobbit, before finally becoming central to the Alpha Plot of The Lord of the Rings.

In Snatch the stolen diamond's story arc starts off in central focus but quickly becomes buried in the movie's tangled plotlines, driving the action only occasionally but always in a significant way, before ending up once again the center of attention at the very end of the film.

Arcs: Prophecy Arc

This kind of arc happens when something is foretold in an early episode and hangs like a shadow over the plot for many episodes to come. Often these arcs are the longest and can have profound influence on the plot as parties try to either cause or prevent the foretold event. When effectively used,  prophecy arc can fade entirely into the background but never leaves people's minds. Prophecy arcs are also the most likely type of arc to cause unexpected twists to happen.

At The Table: Big Battles

In most systems, running a battle with a dozen participants is slow and difficult, but doable. What happens when armies clash and suddenly you're faced with a battle with thousands of participants? Normally a party of players characters should never find themselves in the midst of such a situation. See last week's article for reasons why. Nevertheless sometimes a story really does call for players to stand shoulder-to-shoulder with an army's rank-and-file and fight against an opposing army. Such situations tend to be more common in low-magic settings where the party are less able to wipe the floor with their enemies and level differences are less pronounced.

Today's article is about how to construct an army-vs-army battle and run it without the sheer number of participants making things unworkable.

Setup

Step 1: Terrain

The first step is to determine where the battle is taking place. The battlefield should have natural boundaries to keep it from spilling out (unless that's part of your plan) and anyone leaving the battlefield can be considered removed from the action. Draw a low-detail map encompassing the entire battlefield and highlighting any significant terrain, fortifications, roads, and environmental hazards. Also now is the time to decide on environmental factors like time of day, and weather if they will have any effect at all on the battle.

Step 2: Objectives

Mark on the map where each army's objectives are located. Is there a fortress that the attackers must take? Are the defenders simply holding ground? Are both armies going after each other's generals for some reason? Is one army simply trying to move past the other with as few losses as possible?

Step 3: Strategy

On your low-detail map, mark out roughly where each army will be starting from. Remember that armies are large and often made of several parts, so an army's starting location will be a collection of blobs rather than a single 'x' on your map. If either side is expecting re-enforcements during the battle, also mark where they will enter the battlefield from.

Starting position has a big impact on gameplay. Consider a fortress acting as the starting position for a defending army. How close to that do the attackers start? How much time will the defenders have to strike out at them and reduce their numbers before they reach the fortress's walls? Don't try to make the battle balanced. No army ever willingly walks into a fair fight.

With starting positions determined, decide on the rough routes each army's forces will attempt to take to their objectives, keeping in mind that an army may have a diverse set of units suited to different tasks. Reviewing historic battle maps can be a huge source of inspiration here.

What role does the player party play in the battle?

Step 4: Movement

Divide your low-detail map into sections. The section sizes can be arbitrary but they should generally follow terrain, with some subdividing for large areas of contiguous terrain like fields. For areas with complex terrain such as fortresses, cliffs, etc. divide the map into small, tightly-packed sections.

These sections are used to divide one large battle map into much smaller maps. Each section can be host to a single group of units. For the purpose of this article, a "unit" is a group of 6 or fewer characters, be they PCs or NPCs. Moving into an occupied section provokes an encounter with the units already there. Moving from one section to another may provide temporary benefits (such as when charging downhill) or penalties (such as when entering a forest) to the moving unit. This encourages tactical movement as forces advance across the battlefield.

Step 5: Encounters

Number each section. Now note which sections neighbour each other. If some attribute of the terrain or environment (walls, trees, water, slopes, etc.) between two sections would affect combat in some way, make a note of the effect it will have on any unit moving between those two sections. Now add detail to the sections, focusing mainly on things that will influence combat depending on which direction units come from. Remember that your players will only see a handful of sections so don't paint a masterpiece for each of them. More detail should be added to the sections containing objectives the player characters will be working towards.

Look at both army's composition and either construct full encounters to represent each unit, or simply generate the individual NPC types that will make up either army's units and randomly generate encounters from them on-demand as the battle proceeds. Remember to have stats for both army's forces just in case the players need re-enforcements.

You may be wondering, "if a unit is only up to 6 characters, how many units are in my army of 6000?" Once again this is a case of conservation of detail. The answer is 6000 is a statistic only noticeable from a bird's eye view. On the ground all that matters is who the players are fighting now and who they're fighting next. You can describe a unit as being as large or as small as is fit for the battle. The characters the players don't fight are busy fighting with other characters in the player's unit just off-camera. No need to roll dice for them or even put them on the grid. If the players win their encounter, their squadmates are assumed to also win and advance with them. If the players retreat their squadmates go with them.

Have an idea of the relative strength of each army's soldiers so you can determine outcome of all-NPC combats using a single dice roll.

At The Table

Have your battle map next to whatever surface you normally run encounters on (ie. your combat grid) so that it's in plain view of the players. On the battle map place markers to indicate the positions of friendly and hostile units.

For every unit other than the players, roll a d4 to determine how long that unit will stay in their current section before being able to move. The outcome of the roll may be modified by the size of the section, terrain, and presence of defenders. Keep in mind that a party of highly-trained player characters will generally end battles faster than conscripted foot-soldiers. It may be advantageous to for party to advance at the same rate as their allies or charge forth out ahead of them. A player character unit can move as soon as its current encounter is done.

Continue running encounters for the players and determining all-NPC encounters by diceroll until either army is defeated or completes its objective. If you've prepared well enough this system can produce a great tactical experience for players without bogging down the game with NPC-NPC interactions.

Upcoming Articles

World Building - Weaving Plot Threads: I discuss a storytelling technique commonly used to keep things interesting in long-running or episodic stories.
At The Table - Close-Calls and Character Death: My take on this much-discussed topic.

Note

My queue of articles is running out so I might put this blog on hiatus until I can get more.

World Building: Going to War

If story elements were a chess set, large-scale armed conflict would be the queen. It is one of the most versatile and potent tools available, able to provide background and framing or be a central driving force in the plot. This week I offer my thoughts on how to use war in a variety of ways and some of the pitfalls to be wary of when working it into your campaign. First, some words of caution:

Things to Avoid

PCs as foot-soldiers - Player characters do not belong with the rank-and-file of any nation's army. A character with 2 or more levels in a PC class is much more powerful than a conscripted soldier of any common race and will mop the floor with enemy footmen in battle.

Super-large battles - Going along with the above point, an infantry charge might involve dozens of combatants in the PCs general vicinity alone. Adjudicating a battle using the normal Pathfinder or D&D rules with that many participants takes an absurdly long time and puts incredible mental strain on the GM, not to mention crowding up the battle grid.

Hopeless Scenarios - Defeats happen. While a crushing defeat can be great for a dramatic storyline, being on the losing side with no hope of surviving isn't fun for players. Remember that as a GM your ultimate duty is to provide an enjoyable and engaging experience for your players. Your players should always be able to figure out a way to escape if they try. If your players give up hope, have an NPC or contrivance of luck ready to give them a way out.

Pointless Wars - Wars have causes. Armies have objectives. History may call a war pointless but for the people living through it on either side there is always a goal. Even an army of demons massacring everything in sight with no apparent goal or direction has someone at the top who knows what they're doing it for, and it's usually not "for the lulz".

Types of Wars

No two wars are alike, but they can be grouped into a few categories based on the scope of the action and the parties that are involved:

Border Skirmish - Two neighbouring states who are unfriendly start attacking each other. These conflicts are usually small compared to other wars and involve just two participating states. Often they are started by a perceived insult or provocation and end with no territory gained by either side. This kind of conflict is often used as a background element unless it grows into a full-on invasion.

Rebellion/Insurrection - Often called differently depending on which side you're on. This involves a small force attacking a larger force from within. It often lends itself to guerrilla warfare, espionage, and acts of terror by both sides. It can evolve into a regional conflict if either force gains allies. Of all the different types of war this is the one with some of the best potential as a central plot.

Invasion - One state attacks another state with a weaker army and manages to gain territory. The invaders may simply be seeking resources in some of the invaded territory or may be seeking to completely annex the state. This is often a very active kind of war with battles cropping up frequently as the invading army pushes into new territory. It can start as a looming background threat and suddenly surge to the foreground. A common dramatic plot shift is to have a sudden invasion completely derail the PC's plot train and have the fleeing for their lives until they get a chance to regroup.

Occupation - The part that happens to an invasion-type war after the invading army has passed through and claimed an area. Typically the invading forces will leave behind weaker numbers to quell any chance of rebellion. PCs in an occupied state may have to hide their identities and gather up forces to start a rebellion, or try to break through enemy lines back into their own territory. Resources in occupied areas are usually scarce as soldiers pillage the land for food and goods.

Regional Conflict - A war involving several states in a geographic region. These are the largest and most complex. Often belligerent states may have webs of alliances dictating who they attack and who they support, with the ever-present threat of backstabbing. This kind of large-scale conflict again belongs more in the background, as events are often simply too big and too spread out to give the PCs a significant part in them.

Player Character Roles in War

If you decide to have your player characters close to the action in a war, there are several roles they could take:

Elite Commandos - The most common role and for a good reason. Heroic characters performing daring operations behind enemy lines makes for an engaging and straight-forward plotline.

Lone Survivors - The opposite of commandos in a lot of ways; this role requires characters survive on their wits and skills. Stealth, mobility and subterfuge are key to evading enemy forces. Because of the power gap between high-level PCs and soldiers, this role is best reserved for low-level characters.

Messengers/Arbiters/Diplomats - The player characters act as go-betweens between important parties in the warzone. As messengers it is their duty to get valuable information to its intended parties in a timely manner. As arbiters or diplomats they must unravel the web of relationships between warring parties. These roles are best suited to roleplay-heavy campaigns as there tends to be lots of talking.

Neutral Parties - People not actually part of the war, but who choose to operate in a warzone. Arms dealers looking to make a buck, treasure hunters seeking to loot still-burning ruins, healers helping both sides, and scholars seeking to preserve culture and take records are some roles player characters can play as neutral parties.

Coming Up

I'm going to probably revisit the topic of telling war stories again at some point. Next week's article, At The Table - Big Battles, will be a counterpart to this one describing how to have a huge field battle if you disregard my advice and decide you really do want your characters charging across a battlefield with a bunch of infantry or cavalry.

No article this week.

Been kinda busy lately with personal stuff. It's all good but it does take away time I usually use for writing. Next week's article should be on time.

At The Table: Complex Skill Checks

Often times in more sophisticated campaigns you may want to devise some complex action for the players to perform. Things like repairing a piece of machinery or performing a lengthy magical ritual aren’t well-covered by most rule systems. Often these actions are too important to players’ success or the plot to wager on just one skill check. This is where the concept of complex skill checks comes into play.

What is a Complex Skill Check?

A complex skill check is, at its core, single large action spread across several skill checks. Complex checks are designed for situations where an action will take several combat rounds to complete and in this capacity are useful for adding tension to a high-pressure scenario. Complex skill checks also have varying degrees of success depending on which rolls succeed or fail. That feature makes them useful for checks with no retry, where however far you get is the limit of what you achieve. I’ll provide examples of both uses below.

Building Complex Skill Checks Into Encounters

If you are going to use a complex skill check it should be the focal point of the encounter. The character(s) performing the check will need to devote their full attention to the task at hand. If enemies threaten them the other party members will have to defend them. Damage to a character performing the check may reduce their chance of success. Complex skill checks are also time-consuming, increasing the chances of being interrupted by friends or foes. The farther into the complex task the player gets, the more difficult each individual check becomes, further driving up the tension.

Performing a complex skill check is a lot like spellcasting and for the most part can be treated the same way as concentrating to maintain a spell. Damage to the character increases the difficulty proportional to the damage received, violent motion increases the difficulty my a similar amount, and sudden noises or distractions also increase the difficulty by a predetermined amount.

Performing Complex Skill Checks

If the task involves several actions that can be done in parallel (such as opening a series of valves), then several characters can participate at the same time. They do not grant Aid bonuses to each other. A single character performing a complex action can receive an Aid bonus from a non-participating character if the action being performed would normally allow it (typically physical actions allow assistance and mental actions do not). All participating characters make their skill checks on their own turns if in combat, or simultaneously if not. Once all the dice for one set of actions have been rolled, tally up the successful checks and determine the level of success.

Often complex skill checks require a specific series of steps. Different steps in a series cannot be performed in parallel and typically (but not always) have to be performed by the same character. A failure at one step usually ends the complex skill check, but some complex checks may have branching outcomes that allow for some failures. GMs use your imagination here.

Complex Check Stat Block

Each step of a complex check has several statistics that describe what’s necessary to perform it:
Max participants: The maximum number of characters that can work on this step in parallel
Prerequisites: Things a character must have to participate in this step
Skill check: The skill check each participant must perform during this step
Successes to Proceed: The number of successes needed to proceed to the next step or complete the check. These might be per-participant or a total number overall.
Max Failures: The number of failures, which if surpassed, cause the whole process to fail. These might be per-participant or a combined total.
Time: How long this step takes to perform

Example Complex Skill Checks

Perform Ritual Magic

Step 1: Prepare ritual area
This requires writing a magic circle on the ground
Max participants: 4
Prerequisites: All participants must possess the ability to scribe scrolls
Skill check: Spellcraft DC 5+level of ritual spell
Successes to Proceed: 4 total
Max Failures: 2 total
Time: Two minutes per check (2-12 minutes depending on number of participants and if they need to retry)

Step 2: Set Up Ritual Components
You must correctly arrange the spell components within the ritual circle
Max participants: 4
Prerequisites: Trained in Knowledge (Arcana)
Skill check: Knowledge (Arcana) DC 10+level of ritual spell
Successes to Proceed: 4 total
Max Failures: 2 total
Time: One round per check

Step 3: Perform Invocation
The senior spellcaster stands within the prepared ritual circle and casts the spell
Max Participants: 1
Prerequisites: Must know the ritual spell
Skill check: Spellcraft DC 15+level of ritual spell
Successes to Proceed: 1
Max Failures: 0 (failure destroys ritual circle, requiring start over)
Time: one round


Operate Complex Mechanism

Step 1: Analyze how it works
You must examine the mechanism and correctly deduce how to operate it
Max Participants: unlimited
Prerequisites: Trained in Disable Device
Skill check: Disable Device DC 22
Successes to Proceed: 3 total
Max Failures: 0 per participant (You get the wrong idea about how it works and must stop helping. Other participants may proceed.)
Time: 10 minutes per check

Step 2: Open steam valves
Four valves must be opened in unison
Max Participants: 4 (aid allowed)
Prerequisites: none
Skill check: Strength DC 14
Successes to Proceed: 1 per participant
Max Failures: 0 total (not opening all the valves together causes a small explosion and breaks the machine, making retrying impossible)

World Building: Zoom out to Realm

A Realm is a geographic area that comprises several Regions. It may be the entire extent of an island or the territory of a single nation. Unlike a Region, a Realm's borders need not be defined by natural boundaries. Instead, a realm is usually defined by the people that live in it, their culture, politics, and the flow of resources. A single realm can be considered a self-sufficient territory that is able to produce food and common goods and consume those things within itself.

Gameplay-wise, the majority of a small-to-medium campaign can be played at the realm level. A typical realm is large enough to provide numerous adventure opportunities and a variety of terrains, while at the same time the cultural uniformity reduces the amount of time necessary to spend setting up new NPCs and settings. You can describe the look and feel of a town in this realm once and then while adventuring within the realm players can keep that look and feel in mind so that new towns don't require entirely original design. You may be tempted to make each town and location unique and that's excellent, but towns should be unique in ways that entice players to do things and explore them rather than just having a different style of buildings or different food.

Many of the principles that work at the settlement and region levels. Access to water is still a fundamental requirement for settlements, terrain types should still transition, and the speed of travel still dictates how large an area one government can control. However, as the map zooms farther out things become fuzzier:

Diversity of Resources

At the realm level the rules for deciding where settlements form start to change. Like any good game of Settlers of Catan or Civilization, access to a variety of resources is essential. People will go to amazing lengths to access valuable resources. Water still remains essential for survival, but it might not always come from coastlines or rivers. If there's ore in the mountains settlers may utilize glacier melt for water. Settlements in arid lands might tap underground aquifers or construct extensive viaducts to bring water to places where they want to settle. Areas in your realm that have resources like ore, lumber, or powerful natural magic will attract crafty settlers who make their settlements work somehow to tap those resources.

Trade Routes

The essentials of life circulate within a realm. Water, staple foods, meat, and building materials should all be produced and consumed within your realm. These goods usually won't all be found close to eachother though so they'll probably circulate by trade routes. Trade routes are the main arteries of any realm. They bring goods and information to and from far corners of the land. Usually there are a few large central cities that have markets that act as trade hubs. These will be the most populous and influential settlements in the realm.

Points of Authority

Cities exert influence over the territory around them. If you're building a nation-state there will be usually one capital city and usually a handful of provincial seats-of-power that follow policy from the capital. These provincial powers handle the actual administration of their surrounding regions and are usually the same cities as the major trading markets. If you're building a collection of related feudal states there isn't a capital dictating policy but the noble rulers may still share customs and values that dictate how people act. In the presence of external threats people from across a realm will usually band together to resist and preserve their common culture and way of life.

Evolution & Conservation of Detail

Evolution and conservation of detail go hand-in-hand. A realm is large enough that it's impractical to fully populate in one sitting. Additionally, you want to have lots of low-detail space to fill in with new adventures you come up with. Start with the region the players started in and add progressively less detail the farther from that realm you get. Regardless of how far from the players they are, you should have all major cities, trade hubs, and seats of power drawn on the map with major trading roads joining them.

Drawing a Realm Map

I don't have a super-simple grid-based system for this.

1. Figure out roughly the distances you want your realm to span and determine a map scale that works for you.
2. Draw large terrain features such as ocean coastlines, mountain ranges, and major rivers
3. Determine where resources like lakes, forests, farmland and mines are. These should be consistent with your starting region.
4. Place major trading cities in areas that are:
• On the coast if you have one
• Located very close to one one resource and not very far from others
5. If you're building a nation-state, choose one trading city to be the capital
6. Place adventure sites, towns and smaller settlements in the area around your starting region. Leave plenty of blank space to populate later as players explore the area.

Upcoming Articles

At The Table - Complex Skill Checks: Performing large, complicated tasks with a fistful of dice
World Building - Going to War: War is the backdrop for a great many stories. Bring it to the foreground.

At The Table: Dynamic Difficulty

Ahaha you thought I was going to miss another week, didn't you?

It's a problem every Game Master faces at some point: how to keep the game moving when not all players are present. To some extent Pathfinder is set up to handle this. If you're doing by-the-book encounter generation then you know that encounter challenge ratings are for a range of party sizes and not specific numbers. For instance a party of 4 or 5 people generally have the same challenge ratings, a party 5-6 have a higher one, etc. Often with one player out normal encounters don't get much more difficult, but what about encounters designed to be challenging?

As soon as you pit your diminished party against an encounter that's rated "Hard" or "Challenging" against their full strength you quickly start running into problems. Suddenly that 1-player disadvantage turns into a huge power gap that can turn a fun but challenging encounter into a desperate struggle to survive. This article will outline some techniques to help balance a 1- or 2- player disadvantage and how to apply them depending on what's missing from the party. If more than 2 players are missing, you should probably postpone your game. These tricks can only stretch the encounter rules so far before they risk breaking the game. Also remember that these techniques can be used in reverse to increase difficulty if you feel your party are having too easy a time or if someone's friend wants to join for one game.

Enemy Hit Points

Quite simply, give enemies more or less HP. This is by far the easiest way to adjust encounter difficulty. It can be used to increase or decrease difficulty based on party size and falls within the rules perfectly because most enemies have hit dice that represent a range of possible HP values. The fact that most GMs use the average HP printed on the stat block does not negate the fact that individual enemies may have more or less HP as long as it's a possible outcome from rolling the enemy's hit dice.

The key factor that enemy HP changes is the expected length of the encounter. A enemy with more HP will take more turns to kill, require more attacks, more spell slots, and more healing. If your party is missing damage dealers this is a very easy way to help balance them out. This is less useful with missing support or healing characters because if your damage output is still high you'll probably have time to heal after the encounter is over.

Enemy Gear

This only applies to enemies that wear gear, obviously. If your party is missing healing or support characters, one option is to adjust what gear the enemies are using. With HP adjustments the aim was to control how long the fight goes on for but with gear adjustments the goal is to keep the fight duration the same and instead alter the amount of damage the party take or the party's chances of damaging the enemies. This can make up for the Bless spell from the absent paladin or an application of Channel Energy from a missing cleric. Usually just changing one carefully-selected item is enough to adjust the difficulty. Choosing how to adjust gear can be more difficult than changing HP, however, because gear changes can alter far more numbers and aren't nearly as easy to do on the fly or justify in-universe. For that reason I only recommend using this if you have sufficient time to prepare.

Enemy Number

An obvious way to make an encounter harder or easier is to change the number of enemies encountered. This is easier at low levels when enemies with fractional CRs are common and much more difficult when dealing with packs of CR 5 monsters. The addition or removal of a single enemy can drastically change the difficulty of an encounter, especially when terrain and movement are considered. For this reason I don't recommend just adding or removing a member of a monster pack.

What you can do, however, is alter how long an enemy is in the fight for. This can be done through HP adjustments to just one or two combatants but can also be done by making them cowards. Having an enemy flee combat both limits the duration of the fighting and introduces the exciting possibility of chasing them down or having them go get reinforcements, effectively turning one encounter into two smaller encounters with a short break in between. This can be useful for any party composition, but don't get carried away and string together more than two encounters or you'll risk tiring your players and their characters out too quickly.

Favourable Terrain

As I've described before I like to set up encounters in arena-like spaces and rooms with lots of random set dressing to provide obstacles and cover. This makes battles more dynamic and invites players to come up with novel tactics for overcoming enemy positions. The availability of good cover (especially when fighting ranged attackers) can significantly alter the balance of an encounter.

For example, if your party's primary melee tank is missing you might rebalance an encounter by adding difficult terrain between the party or the enemies that the enemies must cross to engage the party, giving your remaining attackers an extra round to deal damage before the enemies can close to attack their squishy hides. 

Another example might be removing some cover from the enemy's side so it's easier for your ranged attackers to hit them.

If your party is missing its ranged attackers you might remove obstacles from both sides to make it easier for your melee characters to close in.

In any case, these kinds of alterations will alter both the fight length and the enemy's opportunities to do damage, thus giving great flexibility to deal with any deviation from the planned party size.

Favourable Circumstance

For non-combat encounters, how do you deal with missing someone with necessary skills? For instance, what if your best diplomat is absent? Logically you'll want to reduce the DCs of these skill-based encounters to a level such that someone who is present can succeed. The problem then is how to make it not seem artificial. The easiest way for that is to come up with some in-universe circumstance that explains why it's easier. Maybe the shopkeeper the party want to haggle with is of the same race or alignment as the player elected to do the haggling, or maybe a festival in town is distracting the city guard enough to make infiltrating the castle vault easier. Use your imagination and the possibilities are endless.

Double Rolling

Do not use this if you can avoid it because it makes the game less fun. Sometimes when all-else fails you just need to fudge it. Unlike the other techniques which are all numeric changes, this one is the GM playing games with the enemy's luck. Double rolling is exactly what it sounds like: roll two D20s for enemy skill checks, attack rolls, etc and pick the result you want. This has the potential to give the party or the enemies miraculously good luck and tip the balance in the favour of the group you want to win. Obviously this must be used sparingly as it takes a lot of the excitement out of encounters if one side always does poorly. And it's, y'know, cheating. Doing this requires no preparationat all, is not particularly suited to any party configuration, and can change from encounter to encounter if people have to leave mid-game.

Upcoming Articles

World Building: Zooming Out From Region to Realm - More basic geography and defining nation-states
At The Table: Complex Skill Checks - Dice rules for performing more complex actions