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Encounter Design

Exploration Encounters

Exploration entails traveling from one location to another and overcoming whatever challenges the world throws at the adventurers. These are primarily encapsulated by Exploration Challenges.
Dungeons. What constitutes a dungeon can vary widely, but so long as there’s a floor beneath their feet, walls around them, and a ceiling overhead with danger lurking around each corner they’re exploring.
Planar Travel. When a campaign gets the party beyond the realms material and into other dimensions they’ll encounter unfamiliar flora and fauna, denizens they may not even recognize as sentient beings, and wonders they’ll never forget. These journeys can be especially perilous and the powerful magic usually required for them will take adventurers far from their homes, but inspire tales that are retold for centuries.
Urban. Settlements are the primary places where social encounters occur, but can offer a number of other challenges and obstacles.
Wilderness. Most exploration roleplay happens between other types of encounters as the party makes their way through the world, whether by air, land, or sea.

Social Encounters

Whenever the adventurers are interacting nonviolently with NPCs (or maybe sometimes just a little bit violently) they are having some kind of social encounter.
Convince. A fundamental reason for the party to interact socially with NPCs is because they want something. The primary means of convincing others will be their actual roleplaying (what the adventurers say and do), and at the GM’s discretion the use of social skills like Deception, Intimidation, and Persuasion. This isn’t to suggest that other skills (like Arcana, Culture, History and so on) don’t have a role here, but unless it’s a specific situation (such as distracting a fellow mage, an aristocrat, or an historian) they are not the primary means of achieving what the party is after.
Develop. Every social encounter is an opportunity for players to make it clear who their adventurer is, what they’re about, and to discover how they are changed by the world around them and the conflicts they’ve endured. These interactions are vital in making a group feel like they have a stake in what’s going on in the campaign, and can provide narrative resources that might become powerful motivators for other important factors in the game.
Entertain. Social encounters don’t always have to have hidden motives or intended goals, and giving players the opportunity to simply exist in the campaign gives the experience a certain sense of realism. There are other stories being woven around them, not every conflict bears an imminent threat, and even for adventurers there can be pleasant lulls between lethal battles and deadly dungeon delves.
Inform. Probably the most likely reason for social encounters is to provide information to the players.
Occlude. Just as there are times when the adventurers are trying to convince someone to do something, there are occasions where adventurers will need to act so that someone does not do something by concealing important information (thus removing the impetus to act). Typically this is a matter of Deception but might also be a Stealth check or opposed Investigation check.

Combat Encounters

There are two main ways to build a combat scene:
Challenge-Based Encounter. The Narrator may set out to prepare a fun, challenging combat encounter and chooses opponents accordingly.
Story-Based Encounter. Often the story and player actions determine the nature of a conflict. There’s no guarantee that a fight is winnable: the party must deal with the consequences of their choices.

In either case, the Narrator will want to know whether a fight is likely to be trivial, unwinnable, or somewhere in between. In a challenge-based encounter, the Narrator wants to aim for a middle ground of difficulty. In a story-based encounter, the Narrator may want to signal to the adventurers when they’re about to bite off more than they can chew. It’s rarely fun when a crushing defeat or an easy victory is a surprise to everyone (including the Narrator).
To determine the likely challenge posed by a battle, compare its combat encounter difficulty and its maximum monster CR to the party’s capabilities.

Combat Encounter Difficulty

Combat encounter difficulty is evaluated by comparing the encounter CR (the total CR of all opponents) to the total character level. The ratio of these two numbers determines the challenge presented by the matchup.
Allies. If the adventurers have monster or NPC allies, add their CR × 3 to the total character level.
Elites. When calculating the encounter CR, double the CR of elite monsters.

Encounter challenge ratings are flexible and can allow for many different types of battles. For instance, a CR 10 encounter could consist of one CR 10 monster, two CR 5 monsters, one CR 5 leader with five CR 1 minions, and so on.
Here’s how adventurers stack up against monsters:

Easy Matchup

Medium Matchup

Hard Matchup

Deadly Matchup

Impossible Matchup

Low Level Adventurers and Low CR Monsters

Tier 0 adventurers are not extremely tough yet. They have very few hit points and spell slots, as well as limited access to area attacks. A low level party can be easily swamped by large numbers of low CR monsters.
When determining encounter CR for tier 0 or tier 1 adventurers, treat any monster with a CR below 1 as if its CR were one step higher. Thus a CR 0 monster is effectively a CR 1/8 monster when calculating encounter CR, a CR 1/2 monster is effectively a CR 1 monster, and so on. For example, a group of three 1st level adventurers (total character level 3) against two goblins (effective CR 1/2 each, encounter CR 1) is a medium challenge.

TABLE: TIER 0 AND TIER 1 EFFECTIVE ENCOUNTER CR

ACTUAL MONSTER CR EFFECTIVE CR
0 1/8
1/8 1/4
1/4 1/2
1/2 1

Party Optimization

The Combat Encounter Difficulty guidelines assume a party with a standard amount of magical treasure, a healthy but not overwhelming interest in tactics, and a balanced composition of classes that includes a spellcaster or two.
If adventurers are more interested in story immersion and character than in combat, or they possess fewer magic items than usual, then they may prefer mostly easy matchups with a few medium ones thrown in. Similarly, some party compositions, like an all-rogue party, are best suited for easy combat challenges and difficult exploration and social encounters.
If a party is composed of highly experienced players looking for a combat challenge, and they’re playing optimized adventurers of 5th level or higher, the players may relish frequent hard and deadly matchups. They may even want to try their hands at impossible matchups. Similarly, battles can be made more difficult in a campaign rich with magical treasure.

Maximum Monster CR

An encounter’s maximum monster CR is the challenge rating of the single toughest opponent in the encounter.
Adventurers are rarely able to fight a satisfying battle against a monster with a CR that’s much higher than a single adventurer’s level. Such a monster has a high chance of dropping an adventurer from full health to 0 hit points in a single hit, and its defenses and saving throw DCs may make it more deadly than expected. Even if a battle looks possible when comparing the total character level and encounter CR, it is an impossible matchup if the maximum monster CR is higher than 1.5 × the average character level.

Using Elite Monsters

An elite monster is a powerful opponent designed to provide a tough challenge to a large group of players. Often, an elite monster is a variant of another monster: a leader, champion, or even a named individual.
An elite monster has approximately twice the hit points and deals around 50% more damage than a normal monster of its CR—and it usually becomes more dangerous as the battle goes on.
An elite monster poses the same challenge as two non-elite monsters of its challenge rating.
When determining encounter CR, double the challenge rating of an elite monster. However, elite monsters have attacks, defenses, and saving throw DCs that make them suitable opponents for lower level adventurers. When determining the maximum monster CR of an encounter, use its actual CR.

Using Legendary Monsters

A legendary monster is designed to be an interesting combatant for multiple adventurers. With up to 3 legendary actions, and possibly extra bonus actions and reactions as well, it has the extra turns it needs to keep up with as many as three adventurers.
As with any other monster, a legendary monster is at its best when its CR is, at most, 1.5 × the average character level. A maximally tough legendary monster like this is a hard matchup for 3 adventurers, a medium matchup for 4 adventurers, and will probably be easy for 5 or more adventurers.
When designing a climactic, set-piece battle against a legendary monster, make sure to provide it some allies or minions if it’s facing 4 or more adventurers.

The Adventuring Day

As a rule of thumb for how many battles a party can likely handle before it needs a long rest, use a daily budget of encounter points.

For each encounter point it possesses, a party can face one medium encounter before needing a rest. An easy battle costs half an encounter point. A hard battle costs 2 encounter points. A deadly battle costs 4 encounter points.
A low level party can face four easy battles or two medium battles before needing a long rest, and a single hard battle could drain them of resources. A high level party could expect to win through a deadly battle and still have resources to spare, though a second deadly battle might put them in a perilous situation.
This encounter budget is an estimate, and is superseded by the Narrator’s experience with a particular gaming group—some adventurers may not have the resources to meet these benchmarks, and some may blow past them. There’s no rule that says that a party needs to fight a certain number of encounters before bedtime, and the pacing of the adventuring day should be based on the desires of the players and the needs of the story.

Combat Encounter Types

One of the ways to keep combat fresh is to vary the types of battles that the players face. If a game session includes multiple combats their difficulty should be varied. A steady diet of hard encounters can be exhausting for adventurers so a few medium or easy battles should be included if the story allows for it.
The composition of battles can vary too. Some class features and attacks (like a rogue’s Sneak Attack) are very effective against a single monster, while others (like a wizard’s fireball) shine against large groups. Varied encounter composition gives everyone a turn in the spotlight and, conversely, forces everyone to improvise when their go-to moves aren’t optimal. Here are some typical combat encounter compositions.
Solo Fight. Sometimes the story dictates that the players battle a single enemy, such as a dragon. It’s possible to make this a challenging and satisfying battle, though the opponent is starting off at a disadvantage—no matter how much damage a normal monster dishes out, it’s limited by the number of turns it can take compared to a party of heroes. Legendary and especially elite monsters make the best solo opponents.
A legendary monster with a challenge rating equal to or 50% higher than average party level can provide a medium to hard battle against three or four adventurers. For a larger party, an elite monster of this challenge rating is required to provide the same challenge.
Boss and Minions. If circumstances require a big showdown with a single tough opponent, it often makes a lot of sense for this tough enemy to be accompanied by lesser monsters. An archmage or a powerful demon will never let itself be caught alone.
A tough monster with a CR equal to the average party level can keep two or three adventurers busy. For each additional adventurer, add monsters with a CR of 1/3 the adventurer’s level.
Commander and Troops. This is similar to a boss and minions battle, but the troops (not the commander) make up the bulk of the challenge. The commander may provide boosts to its allies.
A monster with a CR of up to 1/2 the average party level can match one adventurer. Each additional adventurer can handle two monsters with a CR up to 1/4 their level each.
Team vs. Team. In this type of battle the numbers of adventurers and monsters are roughly equal. Depending on the desired level of difficulty, the CR of the opposition could be between 1/3 and 1/2 average party level.
Horde. Sometimes a party finds itself wading through an army of lowly mooks. This kind of battle will be very easy for adventurers with access to area attack spells like fireball. On the other hand, it might overwhelm a party of rogues or other adventurers that specialize in damaging a single enemy.
Depending on its composition, a party might be able to deal with a force up to five times its size as long as the total CR of all enemies isn’t higher than half the total character level (remember that for tier 1 adventurers, fractional CRs are doubled!)

Combat Encounter Complications

There are many ways to vary combat encounters other than altering the number of combatants. Unique details of terrain, goals, and enemy strategies create story, add vividness, and unlock tactical options.
Alternate Goals. When an encounter isn’t a battle of attrition, the outcome is determined more by story and circumstance than by encounter guidelines and challenge rating. In a fight featuring a complex trap or other goal, the party is trying to perform some noncombat task while surviving an enemy onslaught.
Ranged Attackers. Ranged attackers, like archers and spellcasters, do best when they’re difficult to reach. Intelligent ranged attackers will arrange to fight behind a barrier, such as a wall or a melee bodyguard.
Shifting Alliances. Instead of two, a battle might be composed of three or more factions. The two weakest sides might form a temporary alliance in order to prevent the stronger side from reaching victory—but betrayal is likely.
Terrain and Hazards. Every conflict is set somewhere, and a vividly described location enhances a scene on a visceral and tactical level. A battlefield with high ground, obstacles, and difficult terrain allows both sides to seek advantage. Usable objects beg adventurers to interact with them.
Choke points like doors are tactically useful—so much so that they can come to dominate a battle, causing gridlock. When there’s a strategically important choke point like a door, it can be good to add an alternate route so that clever attackers can outflank defenders. As choke points go, bridges can be more fun than doors (creatures can be pushed off bridges).
Hazards like steep cliffs and lava pools can be treated like a combatant, boosting the encounter CR of the fight. See Encounter Elements for common combat hazards like frigid water, lava, and yellow mold.
Waves. When reinforcements appear halfway through a fight the overall combat is easier than if both groups had appeared together, but harder than two successive battles with a chance to rest in between. This technique can be used to calibrate the difficulty of a battle and to increase tension as the fight goes on. A second group might notice and respond to a conflict, or it might be scheduled to arrive as part of a regular patrol. Possibly an enemy rings an alarm bell or runs to call for reinforcements, and the second wave doesn’t arrive if the messenger is stopped.

Failure in a Combat Encounter

When preparing a combat encounter— especially a challenging one—it helps to consider what failure might look like. Not every battle is a fight to the death with no quarter given, and while failure may lead to consequences and further difficulties for the adventurers, it doesn’t need to be bad news for the players..
The Narrator probably has an idea of what will occur if the adventurers are triumphant in a battle. But if the adventurers lose, what happens next?

Elite Monsters and Failure

A battle against an elite monster can be one of the riskiest and most taxing combat challenges. In such a battle, consider alternatives to total victory or crushing defeat.
If a party manages to reduce an elite monster to half its hit points, they’ve already done very well. They’ve dealt enough damage to defeat a normal monster of its type. Their reward, of course, is that the monster starts hitting twice as hard. The battle becomes more dangerous just when the party may have used up its best resources—which heightens the tension, and not coincidentally, the danger of the encounter.
When adventurers are down to their last few hit points and spells, and an elite monster is bloodied but not beaten, consider whether the monster really wants to fight to the death. An intelligent creature may be ready to retreat or be amenable to a truce, perhaps even offering treasure if the party will leave it alone. After all, it’s been beaten half to death itself and it could probably use a rest! The adventurers may have earned its grudging respect, and it might want them alive as captives or even allies. There are many ways that a valiant but unsuccessful battle against an elite monster can lead to a partial victory.

Encounter Elements

The world can be a dangerous place and the environment might pose a deadly threat all by itself. In addition to their inherent danger, encounter elements offer ways to enhance the perils of exploration challenges or combat to make both more satisfying.

Acid

A creature that touches acid takes 5 (2d4) acid damage. When a creature first enters into an area of acid or starts its turn there, it takes 10 (4d4) ongoing acid damage. A creature submerged in acid takes 25 (10d4) ongoing acid damage. This damage persists for 3 rounds after the creature leaves the acid. A creature ends all ongoing damage from mundane acid by using its action to wipe away the corrosive liquid.

Brown Mold

Brown mold subsists on heat, drawing away warmth from the environment and creatures around it. Most patches of brown mold have only a 10-foot radius, but the temperature in a 30-foot radius around it is unnaturally cold.
When a creature moves within 5 feet of the brown mold for the first time on a turn or starts its turn there, it makes a DC 12 Constitution saving throw, taking 22 (4d10) cold damage on a failure, or half damage on a success.
Brown mold is not only immune to fire damage but rapidly grows when exposed to flames. When any source of fire happens within 5 feet of a patch of brown mold, the brown mold rapidly expands to surround it in a 10-foot radius. However, any amount of cold damage instantly destroys a patch of brown mold.

Crowd

Throngs of humanoids are difficult terrain, and a creature surrounded by a crowd has disadvantage on hearing- and sight-based checks to perceive outside of it.
In addition, making attacks in a crowd risks collateral damage and the wrath of the throng. When a creature attacks from within a crowd or attacks a target within a crowd, on a miss by 10 or more the attack hits a crowd member and the creature makes a Deception, Intimidation, or Persuasion check (DC 13 + 2 per previous check) to convince the crowd not to attack it. On a failure, the crowd transforms into a commoner mob and attacks, fighting until the creature is reduced to 0 hit points or the commoner mob is bloodied.

Darkness

Darkness comes in two varieties: magical and nonmagical. In nonmagical darkness, creatures with darkvision can see out to the range specified by that trait as if it were dim light. In magical darkness, all vision is blocked. Creatures without darkvision cannot see in mundane or magical darkness. In addition, a frightened creature unable to see because of magical darkness is rattled.

Dense Smoke

Creatures and objects in an area of dense smoke are heavily obscured. When a creature that needs to breathe starts its turn in an area of dense smoke, if it is not holding its breath it makes a Constitution saving throw (DC 10 + 1 per round previous turn in the dense smoke, maximum DC 20) or it begins to suffocate. A creature that covers its mouth and nose with a damp cloth has advantage on this save. Finally, smell-based checks to perceive or track creatures that have spent more than 1 round in an area of dense smoke have advantage until the creature finishes a long rest or takes at least 10 minutes to clean the smoke from itself.

Extreme Cold

At the end of every hour a creature is exposed to temperatures at or below 0° Fahrenheit (–18° Celsius), it makes a DC 10 Constitution saving throw or suffers a level of fatigue. Resistance to cold damage, immunity to cold damage, or wearing cold weather gear grants an automatic success on this save. Creatures native to an extreme cold environment also automatically succeed on their saving throw.
Saving throws made against effects or spells that deal cold damage have disadvantage.

Extreme Heat

At the end of every hour a creature is exposed to temperatures at or above 100° Fahrenheit (38° Celsius), it makes a Constitution saving throw (DC 4 + 1 per hour spent in extreme heat) or suffers a level of fatigue. Resistance to fire damage, immunity to fire damage, or keeping a light pack (less than half carrying capacity) grants an automatic success on this save, whereas a creature wearing medium armor, heavy armor, or heavy clothing has disadvantage. Creatures native to an extreme heat environment also automatically succeed on their saving throw.
Saving throws made against effects or spells that deal fire damage have disadvantage.

Falling

The quickest way to severe harm (or even death) is from falling. Whether from a rooftop, cliff’s edge, treetop, or flying mount, falling can deal a devastating amount of damage. When a creature falls, it takes 1d6 bludgeoning damage for every 10 feet it falls (maximum 20d6) and lands prone.
A creature that falls into water takes half damage, or no damage if it dives with a successful Athletics check (DC equal to the distance it falls divided by 5).

Fire

An area of fire sheds bright light to 10 feet beyond its edges and dim light an additional 10 feet. A creature that touches fire takes 7 (2d6) ongoing fire damage. A creature may end ongoing damage from mundane fire by spending an action to extinguish the flames. Smoke and heat shimmer lightly obscure anything within or on the other side of an area of fire.

Frigid Water

After being in frigid water for a number of minutes equal to its Constitution score, a creature makes a DC 10 Constitution saving throw at the end of each minute or it suffers a level of fatigue. Resistance or immunity to cold damage grants an automatic success on this save. Creatures native to an extreme cold environment also automatically succeed on their saving throw.

Green Slime

This sticky, vibrantly green, slopping slime clings to and mercilessly eats away at flesh, plants, and even metal.
Green slime covers a 5-foot square area or larger, though rarely greater in size than a 20-foot radius. Although it is alive and able to sense with blindsight to a range of 30 feet, green slime has no Intelligence or other ability scores. When green slime senses movement underneath it, it drops towards the ground. A creature in the green slime’s area makes a DC 10 Dexterity saving throw, becoming slimed on a failure.
A slimed creature takes 5 (1d10) ongoing acid damage until the green slime is scraped off with an action. Green slime is destroyed by sunlight, any feature, spell, or trait that cures disease, or any amount of cold, fire, or radiant damage. Wood or metal exposed to green slime instead takes 11 (2d10) acid damage.

Heavy Precipitation

Heavy snowfall makes an area lightly obscured, and Perception checks relying on sight are made with disadvantage. Heavy rain has the same effects, also affecting Perception checks that rely on hearing and extinguishing any open flames.

High Gravity

The ranges of ranged weapons are halved, as are all jump distances. When a creature makes its first attack in a round using a weapon that does not have the dual-wielding property, it makes a DC 12 Athletics check or subtracts 1d4 from its attack rolls for 1 round. Falling damage is treated as twice the distance in the area and there is no maximum amount of damage that can be taken from a fall. For every hour spent in the area, a creature not acclimated to it makes a Constitution saving throw (DC 8 + the number of hours spent in the area) or gain a level of fatigue (maximum 4 levels of fatigue).

Lava

A creature that touches lava takes 16 (3d10) ongoing fire damage. When a creature first enters into an area of lava or starts its turn there, it takes 33 (6d10) ongoing fire damage. A creature submerged in lava takes 55 (10d10) ongoing fire damage. This damage persists for 4 rounds after the creature leaves the lava. A creature ends all ongoing damage from lava by using its action to wipe away the molten rock.

Low Gravity

The ranges of ranged weapons are doubled, as are all jump distances. Falling damage is treated as half the distance in the area. In addition, damage from bludgeoning weapons is reduced by half.

Magnetized Ore

Magnetized ore wreaks havoc on the use of compasses or any natural sense of direction, making both useless within 500 feet.
While within 50 feet of magnetized ore, a creature wearing heavy armor made from metal or attacking with a metal weapon has disadvantage on its attack rolls, Strength and Dexterity checks, and saving throws made against fatigue.

Memory Crystals

Recognizing a memory crystal for what it is requires a DC 20 Arcana check. When a creature with prepared spells is within 30 feet of a memory crystal, at the start of its turn it must make a DC 15 spellcasting ability check or lose one randomly determined prepared spell.
When destroyed (DC 17 Strength check, AC 7, 2 hit points) a memory crystal explodes with dangerous magic in a 10-foot radius. Each creature in the area makes a DC 20 Charisma saving throw, taking 14 (4d6) psychic damage on a failed save, or half as much damage on a successful one.
An area filled with memory crystals requires a creature to succeed on a DC 8 Acrobatics check at the end of each of its turns to avoid breaking any of the dangerous gemstones.

Miring Ground

Sludge, tar, or sufficiently deep and sticky mud can provide real danger to creatures caught in them.
Miring ground is difficult terrain. In addition, when a creature starts its turn in miring ground, it begins to sink and makes an Athletics check (DC 12 + 2 per round spent in the area) to continue moving. On a failure, its Speed is reduced by 10 feet. When this reduces a creature’s Speed to 5 feet or less it begins sinking 1 foot deeper into the miring ground at the end of each of its turns. A sinking creature can be freed with an Athletics check equal to the DC of its last failed check against the miring ground. A sinking creature that becomes submerged begins suffocating if it is unable to hold its breath. Any creature trying to aid a sinking creature must have a solid surface to stand on or a fly speed, but can use ropes or similar means to do so at a distance.

Poisonous Plants

Spotting the telltale signs of vegetation dangerous to touch requires a DC 15 Nature check. Poisonous plants can be as sparse as a few shrubs or as pervasive as fields of harmful groundcover.
When a creature starts its turn within the area or enters the area for the first time on a turn, it makes a DC 10 Constitution saving throw, taking 3 (1d6) poison damage on a failure, or half damage on
a success.

Rushing Liquid

Standing in rushing liquid halves the speed of a creature moving against the current and doubles the speed of creatures moving with it. At the start of each of its turns, a creature in knee-high rushing liquid makes an Acrobatics or Athletics check to keep its footing. On a failure, it is knocked prone and moves a number of feet in the direction of the current equal to the amount it failed the check by (rounded up to the nearest 5 feet). The check is DC 11 if the rushing liquid is knee-high, DC 14 if waist-high, DC 17 if chest-high, and DC 20 if the creature’s feet cannot touch the bottom. A creature moving with the current has disadvantage on this check. A creature driven into a solid object by the current (such as a rock) takes damage as if it had fallen a number of feet equal to the distance it was moved by the current (minimum 1d6 bludgeoning, piercing, or slashing damage). Standing up from prone in rushing liquid requires an Acrobatics or Athletics check with a DC equal to the DC to keep footing. A creature that loses its footing is considered underwater (see below) until it regains its footing.

Strong Winds

Ranged weapon attacks and Perception checks that rely on hearing have disadvantage in high winds. In addition, it extinguishes any open flames, disperses fogs and smoke, and forces any flying creature to land before the end of its turn or fall.

Underwater

A creature that cannot breathe water begins to suffocate underwater once it cannot hold its breath. In addition, creatures without swim speeds have disadvantage on attacks made using any weapon other than a dagger, dueling dagger, javelin, shortsword, spear, or trident. Ranged weapon attacks automatically miss beyond their normal range underwater, and bludgeoning and fire damage are halved. A creature that takes damage while holding its breath underwater must succeed on a concentration check or immediately begin suffocating as if its breath had run out.

Vacuum

An area of vacuum has no air, so creatures that need to breathe must use another source of air or begin to suffocate once they cannot hold their breath. In addition, the area carries no sound, so hearing-based checks made to perceive automatically fail and spells with vocalized components cannot be cast. A creature with its own air supply may cast spells with vocalized components, but still cannot hear. Vacuum is also utterly chilling, dealing 11 (3d6) cold damage to a creature at the start of each of its turns in the area.

Webs

Whether created by massive insects or swarms of smaller creatures, these sticky strands ensnare and capture creatures that fall afoul of them. An area of webs is difficult terrain, and when a creature starts its turn within the area or enters the area for the first time on a turn, it makes a DC 12 Dexterity saving throw or becomes restrained. Restrained creatures can use an action to make a DC 12 Acrobatics or Athletics check, escaping on a success.
A 10-foot cube of webs has AC 10, 15 hit points, vulnerability to fire, and immunity to bludgeoning, piercing, and psychic damage.

Yellow Mold

This sickeningly yellow mold only grows in dark places and is extremely sensitive to movement nearby.
Yellow mold covers a 10-foot radius area. When a creature moves within 30 feet of a patch of yellow mold, at the start of its turn spores are released and it makes a DC 15 Constitution saving throw. On a failure, the creature takes 11 (2d10) ongoing poison damage and becomes poisoned for 1 minute, continuing to take ongoing damage until it is no longer poisoned. At the end of each of its turns, the poisoned creature can repeat the saving throw, ending the effect on itself on a success.
Yellow mold is destroyed by sunlight or any amount of fire damage.

Combining Combat Encounters and Exploration Challenges

When battle breaks out in the middle of an exploration challenge as long as one complicates the other, to calculate the encounter CR add the challenge rating of each together just like multiple monsters..

TABLE: CHALLENGE RATINGS AND EXPERIENCE POINTS

CHALLENGE RATING EXPERIENCE POINTS
0 0 or 10
1/8 25
1/4 50
1/2 100
1 200
2 450
3 700
4 1,100
5 1,800
6 2,300
7 2,900
8 3,900
9 5,000
10 5,900
11 7,200
12 8,400
13 10,000
14 11,500
15 13,000
16 15,000
17 18,000
18 20,000
19 22,000
20 25,000
21 33,000
22 41,000
23 50,000
24 62,000
25 75,000
26 90,000
27 105,000
28 120,000
29 135,000
30 155,000

Challenge Rating

The difficulty of a fight against a monster, besting an exploration challenge, or overcoming an encounter element in either is measured by challenge rating, or CR. A challenge rating helps guide the Narrator in choosing appropriate challenges for a group of adventurers and denotes the amount of experience points to be rewarded afterward.
For a short, easy-to-remember summary of these rules, judge a potential encounter by asking the following questions:

TABLE: ENCOUNTER CR FOR DIFFERENT PARTY SIZES

CHARACTER LEVEL 1ST 2ND 3RD 4TH 5TH 6TH 7TH 8TH 9TH 10TH 11TH 12TH 13TH 14TH 15TH 16TH 17TH 18TH 19TH 20TH
Maximum Monster CR 1 3 4 6 7 9 10 12 13 15 16 18 19 21 22 24 25 27 28 30
Easy battle for 2 adventurers 1/4 1/2 1 1 2 2 2 3 3 3 4 4 4 4 5 5 5 6 6 6
Medium battle for 2 1/2 1 2 3 3 4 5 5 6 7 7 8 9 9 10 11 11 12 13 13
Hard battle for 2 3/4 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Deadly battle for 2 1 3 4 5 7 8 9 11 12 13 15 16 17 18 20 21 22 24 25 26
Easy battle for 3 adventurers 1/2 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10
Medium battle for 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Hard battle for 3 1 1/2 3 5 6 8 9 11 12 14 15 17 18 20 21 23 24 26 27 29 30
Deadly battle for 3 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Easy battle for 4 adventurers 3/4 1 2 3 3 4 4 5 6 6 7 8 8 9 10 10 11 12 12 13
Medium battle for 4 1 3 4 5 7 8 9 11 12 13 15 16 17 18 20 21 22 24 25 26
Hard battle for 4 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Deadly battle for 4 3 5 8 11 13 16 18 21 24 26 29 32 34 37 40 42 45 48 50 53
Easy battle for 5 adventurers 1 2 2 3 4 5 6 6 7 8 9 10 10 11 12 13 14 14 15 16
Medium battle for 5 1 1/2 3 5 7 8 10 12 13 15 17 18 20 21 23 25 26 28 30 31 33
Hard battle for 5 2 5 8 10 13 15 18 20 23 25 28 30 33 35 38 40 43 45 48 50
Deadly battle for 5 3 7 10 13 17 20 23 26 30 33 36 40 43 46 50 53 56 59 63 66
Easy battle for 6+ adventurers 1 2 3 4 5 6 7 8 9 10 11 12 12 13 14 15 16 17 18 19
Medium battle for 6+ 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Hard battle for 6+ 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60
Deadly battle for 6+ 4 8 12 16 20 24 28 32 36 40 44 48 51 55 59 63 67 71 75 80

Challenge Rating Increase

The challenge rating of a combat encounter or exploration challenge can be increased when an encounter element is included so long as it poses an active threat—a cage match near a volcanic pit is more dramatic, but no more dangerous than usual.

TABLE: ENCOUNTER ELEMENT CHALLENGE RATINGS

ENCOUNTER ELEMENT CR INCREASE
Acid +2
Brown mold +2
Crowd +1
Darkness +1/2
Dense smoke +1
Extreme cold +1
Extreme heat +1
Falling +1 per 30 feet (maximum +4)
Fire +2
Frigid water +1
Green slime +1
Heavy precipitation +1/2
High gravity +2
Lava +4
Low gravity –1
Magnetized ore +1/2
Memory crystals +1/2
Miring Ground +3
Poisonous plants +1
Rushing liquid +2
Strong winds +1/2
Underwater +1
Vacuum +3
Webs +1/2
Yellow mold +2