Monthly Archives: May 2014

How to run an ambush

Group checks and the ambush

In “How D&D Next almost made knowledge count” and in “Is it noticed? How to run alertness,” I discussed the inevitable success that comes when a group rolls to gain one success. The reverse of this phenomenon appears when a group makes a check and just one failure can drag down the effort. The designers of d20 role-playing games mostly ignore these issues.

Credit the fourth edition Dungeon & Dragons designers for introducing a group-check rule for some tasks. From a game-play perspective, I like 4E’s group-check rule because it makes some group tasks possible. From a realism perspective, I fail to understand how three stealthy party members cover the racket from the clanking dwarf and paladin. In this post, I ignore the 4E rule, which I’ve never seen applied to perception anyway.

No situation highlights the problems of group checks more than the ambush. Using the simplest interpretation of the rules, everyone in a group setting an ambush must roll to hide, giving all a chance to doom the effort with a single bad roll. When the targets of the ambush arrive, every target gets a chance to spot that worst hider.

Based on real life, you might suppose that ambushes typically work. The group setting the ambush has the advantage of planning, preparation, and surprise. They just sit out of sight until their targets arrive. Unless someone sneezes or the targets have x-ray vision, the ambush works.

Based on the game, the word “ambush” describes a imaginary event that can never happen.

In “Is it noticed?” I suggested a fix. I advised assuming that the targets of an ambush take-10 to spot it. In effect, you set the DC for the ambushers’ hide check based on the targets’ lowest take-10 to spot. While this enables one creature to set an ambush, it still fails when a group prepares an ambush and everyone must roll to hide. My method only gives a group a chance of setting an ambush if the GM either (a) requires just a single hide check from the worst hider or (b) relies on 4E’s group check rules for the attempt to hide.

In a comment, Sr. Rojo suggested a method for handling ambushes that I like better.

How to run an ambush

To run an ambush, follow these two steps:

  1. Allow the group setting the ambush to take-20 in their effort to hide.This reflects their time advantage, which lets them pick a good site and then arrange themselves for maximum concealment. When you set an ambush, you have time to work out the best hiding place you can muster.
  2. When the targets reach the ambush site, ask them to roll to spot. The DC to spot the enemy equals 20 plus the ambushers’ worst hide bonus.Unless the ambushers stink at hiding, the DC to spot the ambush may be unattainable for some targets, and will present a challenge to the rest. Unlike most group spot checks, this check presents a reasonable chance of failure. Rather than assuming the targets of the ambush take 10 on their spot check, you can let them roll, and still give the ambushers a fair chance.

As with any spot check, you can limit the check to those characters keeping watch and in position to notice. If the party wants to an ambush a company, only the few soldiers on watch get a spot check, not all 100 enemies.

Take 20 and the rules

“When you have plenty of time, you are faced with no threats or distractions, and the skill being attempted carries no penalties for failure, you can take 20.” – Pathfinder Roleplaying Game Core Rulebook, p.86

Some rules lawyers might argue that the hide attempt does not qualify for a take-20, because it carries a penalty for failure. I disagree. Unlike climbing or disabling a trap, the act of perfecting a hiding spot carries no penalty for failure. Your best hiding place may not be good enough, but that comes later.

Dungeons & Dragons fourth edition and fifth edition both lack a take-20 rule, so this method requires some latitude with the rules as written. In practice, if the players set an ambush and you tell them they automatically roll a 20 on their hide check, no one will gripe.

If the players walk into an ambush, you, as the game master, set the DC they must reach to spot the ambush. Even in a game without a take 20 rule, a DC equal to the ambushers’ worst hide bonus plus 20 makes a good target.

Next: Is it found? How to handle a search

Is it noticed? How to run alertness

Introducing the spot check

In this post, I cite “spot checks” to refer to third edition’s Spot checks, Next’s Wisdom (Perception) checks, and tests of awareness made with 4E and Pathfinder’s Perception skill.

The Spot skill and its descendents rate a character’s ability to notice something while doing other things like traveling, fighting, or resting. Before Spot entered the game, unless you searched, you noticed the things the game master decided you noticed. A thief might hide from you, but their success depended on their roll to hide, not on your ability to spot.

Spot the spider

Can you see me?

When the game master simply decides what the characters perceive, the game plays fine. After all, the game master adds things to an adventure to enrich the adventure. If you let the dice say that the PCs fail to catch a scent of brimstone, or fail to spot the cloud of bats erupting from the cliffside, then the game suffers.

Nonetheless, when Spot skill entered the game, game masters and designers dutifully worked spot checks into every situation. Whenever the party opened a door or topped a hill, everyone made a new round of spot checks. At some game tables, every bit of information had to be earned with a spot check.

I will explain why you should skip many spot rolls, reserving the spot check for a small number of specific circumstances.

Passive perception and taking 10

Fourth edition attempted to rein in spot rolls by introducing passive perception. In principle, a dungeon master could skip perception rolls and use the characters’ passive perception to determine just what they notice as they explore.

“Passive perception checks help you set the scene. They tell you right away how much of the details of a room or encounter area the characters notice.” – Fourth edition Dungeon Master’s Guide p.26

Passive perception extends the mechanic of taking-10. Instead of players stating that they take 10, the game master assumes it.

Passive perception avoids putting the players on alert by asking for a roll when they see nothing. And it avoids interrupting the narrative for all those rolls.

What’s not to like?

The problem with passive perception

Passive perception forces the dungeon master to do the extra work of tracking all the passive perception scores and of setting perception DCs. Typically, this extra effort only yields a process that amounts to the DM deciding in advance what the PCs will notice. Seem familiar?

Most DMs running for regular groups know the approximate perception bonuses of the PCs. If you bother to create something interesting or something that advances the adventure, would you hide it behind a DC that prevents the group from ever seeing it? Never. Not even authors of published adventures will hide things that enrich the adventure beyond the perception of a typical party.

Secrets add fun to the game, but only when uncovered. If the players overlook the secret door, it’s just another wall. – Monte Cook, “Dungeoncraft” in Dungeon 137

But suppose a virtuous DM devises an adventure that gives keen-eyed parties a significantly different experience than unwary parties. The players still never know that their keen-senses paid off. The work of managing perception stays in the DM’s head, its effects unnoticed by the players, extra work, arguably for nothing.

If you would set the DC required to spot something within the reach of the PCs’ passive perception or take-10 value, then skip the DC. They spot it. The players will not ask you to show your work.

As a diceless method of resolving spot checks, passive perception falls short, but it still works as a way to set a difficulty class. More on that later.

The play value of rolling to spot

None of this means that you must always decide in advance what the players see. Random rolls can add an element to the game.

  • Unpredictability makes role-playing games interesting, mainly for the game master. The printed adventure cannot surprise the GM. Only the players actions and the random luck of the die add surprises to the game.
  • Randomness helps the game master keep some distance from the characters’ fates. The players should see the course of the game determined by their choices and by the luck of the die, not by the GM’s whims and mood.

Ask for spot checks (a) when success is uncertain, and (b) success hinges on keen senses in the game world.

Group perception checks almost always succeed

The outcome of group perception checks is rarely uncertain enough to merit a check.

Anytime every player can attempt a spot check, someone will succeed. Suppose a party of five adventurers, all with +0 to their check, passes something that requires a spot DC of 15, what D&D Next considers a moderate DC. If one person rolls, the chance of success is 30%. If everyone rolls, each has a 30% chance of success, which means the odds of someone succeeding grows to 83%. This supposes that no one is particularly good at spotting—everyone has a +0. One alert character pushes the chance of success closer to 90%.

When the odds of everyone missing something amounts to a rare fumble, does stopping the action to roll make sense? With some groups, absolutely. In particular, younger players love to roll, so group rolls create excitement despite the minimal chance of failure. Let them roll.

“Listen or Spot checks can get repetitive and dull if players have to make them over and over, especially when it usually only takes one success out of the whole group to succeed, making their success typically a foregone conclusion. Think twice before asking for such checks. They’re interesting when the PCs are trying to find a hiding or invisible foe, but get dull fast when they’re walking through the woods and you ask for them for every hour of travel.” – Monte Cook, “Dungeoncraft” in Dungeon 137

For most groups, you can consider any ordinary group perception check an automatic success. Skip the pointless activity, tell them what they see, and move on.

When you devise adventures, never mistake a group perception task difficulty for a challenge. On the rare occasions a group fails to spot something, they fumbled. This certainty is not a bad thing. In most cases you want the players to spot the “hidden” things in your adventure, either because these interesting things enrich the adventure, or because they advance the plot.

Hard checks change the equation. These checks impose DCs so high that only one or two members of the party can even hope to succeed. That’s the water elemental stirring the reeds under the bridge, or the key glimmering below the school of silvery fish. In these cases, allow a roll. You must be comfortable with the likelihood that no one will spot the ambush or the key.

If your players have become accustomed to calling for group perception checks, you can tell them not to waste their time, or you can let them have their fun, knowing that their success is virtually certain.

Individual perception checks may merit a roll

Of course, many spot checks can only be attempted by a character or two. This gives you a chance to add an element of uncertainty, and gives your players a potential reward for investing in perception.

Sometimes a spot task may be limited to the characters…

  • leading the party in marching order.
  • with darkvision or another requisite ability
  • spending an action the heat of battle to look
  • with applicable talents such as the ability to spot traps or arcane phenomena
  • taking the role of lookout

The D&D Next exploration system turns some of these limitations into specific rules: “When a character chooses to keep watch as an exploration task, the character makes a Wisdom (Perception) check to detect hidden creatures and an Intelligence (Search) check to detect hidden objects (such as traps and secret doors) as the group travels during the current exploration turn.”

D&D Next writes this as a rule, but it applies to other games too. In many situations, only a few members of the party can make perception checks. Their skills pay here. Keeping watch is a task akin to mapping or tracking.

“Don’t be afraid, in some cases, to only allow one or two characters to make the check. It’s with in your prerogative to rule that most of the party is preoccupied in other activities while one character is more or less ‘keeping watch.’ This isn’t covered in the rules, but in a case-by-case basis, you can decide that only a character who’s trying to listen or keep an eye out has a chance of making a check.” – Monte Cook, “Dungeoncraft” in Dungeon 137

Group perception checks guarantee success, so individual checks like these represent a chance for players who invested in perception skills to reap benefits.

Even if only one or two characters can possibly notice something, you might ask all the players to make the roll, and then only consider the checks from those able to notice. This avoids giving clues about, say, the location of the breeze coming from the unseen exit.

Favor search over spot

Before you ask for a spot check, consider whether a search makes more sense. In most cases, this comes down to the circumstances, see “Choosing which type of perception check fits a situation.” Sometimes, you may be tempted to give someone a chance to spot something hidden, but hypothetically visible to spot. Favor making the players search. Searching plays better than spotting for a couple of reasons:

  • Searching engages the characters in action, forcing them closer for a look.
  • Searching invites the players to make decisions about when, where, and how to search, and how much time to risk.

If someone steps into a room, aces a die roll, and sees the key at the bottom of the fountain and the odd scratches on the floor behind the chest, you have replaced the interaction and decision making demanded by a search with an abstract roll.

Hiding and sneaking

When one creature attempts to hide from others, do not ask for spot or listen checks. Instead, use passive perception or take-10 scores to set the DC to sneak or hide. Pit the active creature’s stealth check versus the highest applicable take-10 score. In the case when a group could roll to spot, this method makes hiding possible, because group perception checks virtually always succeed.

In combat, if someone chooses to look for a hiding creature, they can spend an action and roll versus the hiding creature’s check. In Pathfinder and 3E, active looking takes a move action. In 4E, active looking takes a standard action.

The same system works for ambushes. If someone hides to ambush, they roll to hide. Later, when the ambush springs, compare the hide check against the highest passive perception or take-10 score of the targets.

While this procedure may not follow your game’s written rules, it makes sense because the targets of the ambush are busy traveling and, by default, taking 10 on perception.

Five questions to ask before calling for a Spot check

The game master almost always asks players to make spot checks, except when players take an action in combat to look for something.

As a game master, before you ask for a check, consider these five questions:

  1. Is something sneaking or hiding? Skip the spot check. Instead, use the party’s best take-10 (passive perception) scores to set the DC for the hide or sneak attempt.
  2. Can the thing to spot be noticed from the character’s vantage? If not, wait for the players to search.
  3. Does noticing something fall within the take-10 value of the most perceptive PC? Do not roll. Something is noticed.
  4. Does everyone in the party have a chance to notice something? Do not roll. Something is noticed.
  5. Are only one or two characters in position to notice something? Ask for a perception check.

Next: How to run an ambush

Dead in Thay Player’s Handout

I’m interrupting my series of advice on observation and perception to present a player’s handout that anyone running the Dead in Thay Encounters season will need last week.

Dead in Thay features teams of adventures raiding the sprawling Doomvault dungeon compound. The adventure stands as a great idea for an Encounters season, because multiple parties can simultaneously raid as they seek and destroy Szass Tam’s Phylactery Vault. Each week, groups can reform and stage forays into the complex. This premise delivers the fun of multi-group play, while avoiding the usual Encounters issues caused by a changing cast of players.

As much as I like the concept, Dead in Thay presents players with a daunting amount of background information that they must understand. During my first session, as I tried to explain how the Doomvault operates, and as my players struggled to digest a fraction of it, I realized that the adventure screams for a player’s handout.

So I created one.

You can read the content of the handout at the end of this post. You can download a PDF version of the handout here.

Next: We return to our regularly scheduled posts on observation and perception at the game table.

Dead in Thay Player’s Handout

The Doomvault

You begin in an unmapped Gatehouse with teleportation circles that provide access to the Doomvault.

The Doomvault hides a Phylactery Vault containing the souls of the liches who serve the Thayan leader, Szass Tam. Groups assaulting the Bloodgate slew the lich Tarul Var, one of these undead servants. Tarul Var may have reformed in the Doomvault, near his phylactery. He poses a deadly threat. In the Doomvault, you must gain access to the Phylactery Vault and destroy it. As you explore, seize opportunities to destroy the Red Wizards’ monstrous creations.

Dread warriors patrol the Doomvault. After one round, even from a distance, Tarul Var can take control of any dread warrior not accompanied by other Red Wizards. Not only does this alert the lich to your presence, but he can also cast spells through the dread warrior.

Your ally, the paladin Isteval, has lent each party a circlet of limited telepathy, which enables you to communicate with the other parties inside the Doomvault.

The Doomvault consists of 9 sectors, each subdivided into 4 zones. To begin, each party may choose to enter a zone through the black gates mapped in areas 1, 23, 33, 38, 49, 61, and 77.

Glyph Keys

Glyph keys are crystal pendants on bronze chains, which open magical gates in the Doomvault. Glyph keys can be attuned to the zones in the Doomvault complex.

Syranna gives each party one glyph key attuned to the zone they choose to enter first.

Somewhere in each zone is a Contact Stone marked by a circle of magic glyphs. Someone at a contact zone holding a glyph key can speak to Syranna in the Gatehouse.

You can attune a glyph key to a zone in one of two ways:

  • Copy an attunement from one key to another. A different creature must hold each key, and then one of the holders must spend an action to make a successful Intelligence (Arcana) check.
  • Bring a glyph key to a Contact Stone, where Syranna can attune the key to the zone where the stone is located.

A glyph key can be attuned to more than one zone.

White and Black Gates

The Doomvault includes two types of magical gates.

White gates create walls of force that bar passage. To open a white gate, you must carry a glyph key attuned to one of the zones bordering the gate.

Black gates enable teleportation to other black gates in the Doomvault. Black gates follow these rules:

  • To enter a black gate, you must hold a key attuned to the zone where the gate is located.
  • To teleport using a black gate, you enter the gate and think of your destination.
  • Anyone who enters a black gate may teleport to the Gatehouse.
  • Anyone who enters a black gate may teleport to the Seclusion Crypt, a demiplane only accessible by your characters, which offers you a place to rest and recover.
  • To teleport from the black gate to a black gate in another zone, you must have a glyph key attuned to the destination zone.

You can teleport from the gatehouse to black gates in the complex using a glyph key attuned to the destination zone.

With either type of gate, someone holding a properly attuned key can stand in the gate and hold it open so others can pass. With black gates, the person holding the key decides on the destination.

The Seclusion Crypt

The Seclusion Crypt appears as an empty chamber, isolated in time and space. While time passes in this demiplane, no time passes in the world. This magic causes you to age one month for each hour spent in the crypt. Each time after the first time a character visits the crypt, the character’s hit point maximum drops by 5 until the character can complete a long rest outside the crypt.

Secrecy, metagaming, and perception checks

When players roll their own perception checks, they learn something from the number on the die roll. Players with bad rolls know that their search may have missed something; players with great rolls may trust the game master’s report that they found nothing.

As a game master, you can make perception checks in secret, but players hate this. Some of the fun of the game comes from rolling dice. If the GM rolls for your character, you start to feel a loss of ownership. You feel like a bysander watching the game rather than participating.

Who should roll perceptions checks?

Clear box for dice rolling

Clear box for dice rolling

Many players take pride in running their character without relying on any metagame information. These players can roll, obviously blow their check, and press ahead knowing that if a trap awaits, they missed it. If you have such players at your table, let them roll their own checks. Still, even for these players, knowing the rolls can rob the adventure of some sense of peril and mystery.

Some players take the unearned information that comes from the number on the die and they use it to make choices. For them, remind them that their characters don’t know they blew a search check, so the characters lack any reason to repeat the search. If they keep searching anyway, roll the second check for them, out of their view. And if you simply ignore the second roll, no one will know.

Roll substitution

If you want a game that emphasizes a sense of challenge and risk—or you have a table of unrepentant metagamers, I suggest an occasional roll substitution.

Tell the players, “Whenever you make a perception check, I will secretly roll a d6 and a d20. If I roll a 1 on the d6, the information I tell you will be based on my d20 roll rather than on yours.”

With this approach, most of the players’ rolls still apply, so players remain connected with the game. The visible roll gives the players a fair sense of how their characters performed, just as you might have a sense of your performance on a real-world test. But players can never feel certain that a 19 on the die means they found everything to find. And when someone rolls a 1, but sees a glimmer on the horizon, it may be more than a mirage.


If you only ask for perception checks when something can be noticed, the checks will put players on alert. Once or twice a session, when nothing can be found, you should call on players to make a Spot or Perception check. No matter what the roll, frown, shake your head, and tell them nothing. Not only will this unnerve the players, but it trains them to avoid assuming that they must have missed something.

Next: Is it noticed? How to run alertness

Choosing which type of perception check fits a situation

Both fourth edition Dungeons & Dragons and Pathfinder apply a single Perception skill to all observation tasks. This cuts any confusion about which skill applies. Both D&D Next and third edition split the single skill into two or three.

3E D&D check 4E & Pathfinder check D&D Next check
Search Perception Intelligence (Search)
Spot Perception Wisdom (Perception)
Listen Perception Wisdom (Perception)

Magnification specs

For more on the advantages of multiple observation skills, see “A short history of perception in Dungeons & Dragons.”

In this guide, I sometimes refer to the perception tasks as Search, Spot, and Listen. In your game, apply the skill or check that fits the task.

Choosing which type of check fits a situation

D&D Next offers two types of observation checks, Intelligence (Search) and Wisdom (Perception), raising questions about which applies to a situation.

Spot and alertness checks

Wisdom (Perception) could have almost been called Alertness as these checks cover general awareness. When choosing whether to make these checks, consider the following observations:

  • Characters usually make Wisdom (Perception) or Spot checks to notice something while they’re busy doing something else: traveling, fighting, and so on.
  • Characters usually make Wisdom (Perception) or Spot checks because the game master calls for the check. The characters are busy, but the game master wants to determine if they notice something unusual. Characters make Wisdom (Perception) rolls when they look but don’t touch.
  • Wisdom (Perception) and Spot match with Tarzan’s alertness.
  • Wisdom (Perception) checks show keen senses too, but this typically only applies in one situation: Characters listening at a door make Wisdom (Perception) checks.

Search checks

Intelligence (Search) checks apply when characters spend time to examine and investigate.

Characters make Intelligence (Search) checks when players call for the check by asking to search.

Intelligence (Search) matches with Sherlock Holmes’ use of intellect of observe.

If you spend a moment to scan the surrounding trees, or press your ear to a door to hear what might lurk beyond, you’re relying on Wisdom (Perception) rather than Intelligence (Search). As a rule, if you’re not positive that Intelligence is the right choice, then Wisdom is the ability to use.” – D&D Next playtest rules

Listen checks

Third edition included a Listen skill as a nod D&D’s long tradition of characters putting their ears to doors. Aside for listening at doors, Listen skill frequently overlaps with Spot. When characters might both see and hear something like the monsters sneaking close to ambush, just roll to spot. Allowing characters to use both Listen and Spot to notice one thing makes stealth too difficult and adds excessive die rolling. Reserve Listen for cases where nothing can possibly be seen.

Next: Secrecy, metagaming, and perception checks

Game masters guides fail to give perception enough attention

In the early days of Dungeons & Dragons, perception worked by a simple system: To find hidden objects, players said where they wanted to look, and the dungeon master said if something was there. This method has advantages: It rewards player skill and ingenuity and allows the players to engage with the game world. The features of a location become more than fluff to be glossed over in favor of a search check.

The Hack & Slash blog makes a case that the say-where-you-look method should be the only method.

For all these advantages, the say-where-you-look method suffers a few limitations:

  • It leads to tedium as players spell out how their characters probe, sift, and break down every object the game master mentions.
  • The characters in the game world (and the game master) have a better image of the location than the players, which can lead to oversights and confusion.
  • Some secrets require keen senses in the game world to spot, such as the secret door that, even in original D&D, required a roll to notice.

Game masters guides: long on mood music, short on observation

In “A short history of perception in Dungeons & Dragons,” I recapped how D&D added various perception checks to fix these limitations. But the added checks introduced new issues.

I checked.

I checked.

As perception checks invaded the process of spotting and finding, questions arose. Does the DM decide to make a check or the players? Who gets to roll? If everyone rolls, how do I deal with the almost inevitable success, and should I even bother calling for a check? How can I prevent all the rolls from slowing the game? How can I prevent checks from nullifying player skill and ingenuity, and from making the details of the game world irrelevant?

When I scoured the web for advice on running search and perception tasks, I found no shortage of game masters with such questions. But when I referenced a pile of published advice on running a game, I found scant advice. My fat gamemastery tomes include more advice about mood music and snacks at the game table than about perception. Clearly, the writers of dungeon master’s guides operate on intuition and experience and they never consider these questions—or they cannot answer them.

In my next series of posts, I aim to to better. I suggest ways to avoid long recitals of places to look, and to avoid pointless die rolling. My advice for handling player observation and perception favors player ingenuity and choice over rote and chance, while accepting that sometimes observation depends on a character’s skill.

Next: Choosing which type of perception check fits a situation