Rules Index


Encounter Mode

Source Core Rulebook pg. 468
When every individual action counts, you enter the encounter mode of play. In this mode, time is divided into rounds, each of which is 6 seconds of time in the game world. Every round, each participant takes a turn in an established order. During your turn, you can use actions, and depending on the details of the encounter, you might have the opportunity to use reactions and free actions on your own turn and on others’ turns.

Structure

Source Core Rulebook pg. 468
An encounter is played out in a series of rounds, during which the player characters, adversaries, and other participants in the encounter act in sequence. You roll initiative to determine this order at the start of the encounter and then play through rounds until a conclusion is reached and the encounter ends. The rules in this section assume a combat encounter—a battle—but the general structure can apply to any kind of encounter.

Step 1: Roll Initiative

Source Core Rulebook pg. 468
When the GM calls for it, you’ll roll initiative to determine your place in the initiative order, which is the sequence in which the encounter’s participants will take their turns. Rolling initiative marks the start of an encounter. More often than not, you’ll roll initiative when you enter a battle.

Typically, you’ll roll a Perception check to determine your initiative—the more aware you are of your surroundings, the more quickly you can respond. Sometimes, though, the GM might call on you to roll some other type of check. For instance, if you were Avoiding Notice during exploration (page 479), you’d roll a Stealth check. A social encounter could call for a Deception or Diplomacy check.

The GM rolls initiative for anyone other than the player characters in the encounter. If these include a number of identical creatures, the GM could roll once for the group as a whole and have them take their turns within the group in any order. However, this can make battles less predictable and more dangerous, so the GM might want to roll initiative for some or all creatures individually unless it’s too much of a burden.

Unlike a typical check, where the result is compared to a DC, the results of initiative rolls are ranked. This ranking sets the order in which the encounter’s participants act—the initiative order. The character with the highest result goes first. The second highest follows, and so on until whoever had the lowest result takes their turn last.

If your result is tied with a foe’s result, the adversary goes first. If your result is tied with another PC’s, you can decide between yourselves who goes first when you reach that place in the initiative order. After that, your places in the initiative order usually don’t change during the encounter.

Step 2: Play a Round

Source Core Rulebook pg. 468
A round begins when the participant with the highest initiative roll result starts their turn, and it ends when the one with the lowest initiative ends their turn. The process of taking a turn is detailed below. Creatures might also act outside their turns with reactions and free actions.

Step 3: Begin the Next Round

Source Core Rulebook pg. 468
Once everyone in the encounter has taken a turn, the round is over and the next one begins. Don’t roll initiative again; the new round proceeds in the same order as the previous one, repeating the cycle until the encounter ends.

Step 4: End the Encounter

Source Core Rulebook pg. 468
When your foes are defeated, some sort of truce is reached, or some other event or circumstance ends the combat, the encounter is over. You and the other participants no longer follow the initiative order, and a more free-form style of play resumes, with the game typically moving into exploration mode. Sometimes at the end of an encounter, the GM will award Experience Points to the party or you’ll find treasure to divvy up.

Turns

Source Core Rulebook pg. 468
When it’s your turn to act, you can use single actions (Single ActionSingle Action), short activities (Two ActionsTwo Actions and Three ActionsThree Actions), reactions (ReactionReaction, and free actions (Free ActionFree Action). When you’re finished, your turn ends and the character next in the initiative order begins their turn. Sometimes it’s important to note when during your turn something happens, so a turn is divided into three steps.

Step 1: Start Your Turn

Source Core Rulebook pg. 468
Many things happen automatically at the start of your turn— it’s a common point for tracking the passage of time for effects that last multiple rounds. At the start of each of your turns, take these steps in any order you choose:
  • If you created an effect lasting for a certain number of rounds, reduce the number of rounds remaining by 1. The effect ends if the duration is reduced to 0. For example, if you cast a spell that lasts 3 rounds on yourself during your first turn of a fight, it would affect you during that turn, decrease to 2 rounds of duration at the start of your second turn, decrease to 1 round of duration at the start of your third turn, and expire at the start of your fourth turn.
  • You can use 1 free action or reaction with a trigger of “Your turn begins” or something similar.
  • If you’re dying, roll a recovery check (page 459).
  • Do anything else that is specified to happen at the start of your turn.
The last step of starting your turn is always the same.
  • Regain your 3 actions and 1 reaction. If you haven’t spent your reaction from your last turn, you lose it—you can’t “save” actions or reactions from one turn to use during the next turn. If a condition prevents you from being able to act, you don’t regain any actions or your reaction. Some abilities or conditions (such as quickened and slowed) can change how many actions you regain and whether you regain your reaction. If you lose actions and gain additional actions (such as if you’re both quickened and slowed), you choose which actions to lose.

Step 2: Act

Source Core Rulebook pg. 469
You can use actions in any order you wish during your turn, but you have to complete one action or activity before beginning another; for example, you can’t use a single action in the middle of performing a 2-action activity. What actions you can use often depend on your class features, skills, feats, and items, but there are default actions anyone can use, described in Basic Actions below. Some effects might prevent you from acting. If you can’t act, you can’t use any actions, including reactions and free actions.

If you begin a 2-action or 3-action activity on your turn, you must be able to complete it on your turn. You can’t, for example, begin to High Jump using your final action on one turn and then complete it as your first action on your next turn.

Once you have spent all 3 of your actions, your turn ends (as described in Step 3) and the next creature’s turn begins. You can, however, use only some of your actions and end your turn early. As soon as your turn ends, you lose all your remaining actions, but not your reaction or your ability to use free actions.

Step 3: End Your Turn

Source Core Rulebook pg. 469
Once you’ve done all the things you want to do with the actions you have available, you reach the end of your turn. Take the following steps in any order you choose. Play then proceeds to the next creature in the initiative order.
  • End any effects that last until the end of your turn. For example, spells with a sustained duration end at the end of your turn unless you used the Sustain a Spell action during your turn to extend them. Some effects caused by enemies might also last through a certain number of your turns, and you decrease the remaining duration by 1 during this step, ending the effect if its duration is reduced to 0.
  • If you have a persistent damage condition, you take the damage at this point. After you take the damage, you can attempt the flat check to end the persistent damage. You then attempt any saving throws for ongoing afflictions. Many other conditions change at the end of your turn, such as the frightened condition decreasing in severity. These take place after you’ve taken any persistent damage, attempted flat checks to end the persistent damage, and attempted saves against any afflictions.
  • You can use 1 free action or reaction with a trigger of “Your turn ends” or something similar.
  • Resolve anything else specified to happen at the end of your turn.

    Basic Actions

    Source Core Rulebook pg. 469
    Basic actions represent common tasks like moving around, attacking, and helping others. As such, every creature can use basic actions except in some extreme circumstances, and many of those actions are used very frequently. Most notably, you’ll use Interact, Step, Stride, and Strike a great deal. Many feats and other actions call upon you to use one of these basic actions or modify them to produce different effects. For example, a more complex action might let you Stride up to double your Speed instead of just up to your Speed, and a large number of activities include a Strike.

    Actions that are used less frequently but are still available to most creatures are presented in Specialty Basic Actions. These typically have requirements that not all characters are likely to meet, such as wielding a shield or having a burrow Speed. In addition to the actions in these two sections, the actions for spellcasting can be found on pages 302–305, and the actions for using magic items appear on pages 531–534.

    Aid Reaction

    Source Core Rulebook pg. 470
    Trigger An ally is about to use an action that requires a skill check or attack roll.
    Requirements The ally is willing to accept your aid, and you have prepared to help (see below).
    You try to help your ally with a task. To use this reaction, you must first prepare to help, usually by using an action during your turn. You must explain to the GM exactly how you’re trying to help, and they determine whether you can Aid your ally.

    When you use your Aid reaction, attempt a skill check or attack roll of a type decided by the GM. The typical DC is 20, but the GM might adjust this DC for particularly hard or easy tasks. The GM can add any relevant traits to your preparatory action or to your Aid reaction depending on the situation, or even allow you to Aid checks other than skill checks and attack rolls.

    Critical Success You grant your ally a +2 circumstance bonus to,the triggering check. If you’re a master with the check you,attempted, the bonus is +3, and if you’re legendary, it’s +4.
    Success You grant your ally a +1 circumstance bonus to the triggering check.
    Critical Failure Your ally takes a –1 circumstance penalty to the triggering check.

    Crawl Single Action

    Move
    Source Core Rulebook pg. 470
    Requirements You are prone and your Speed is at least 10 feet.
    You move 5 feet by crawling and continue to stay prone.

    Delay Free Action

    Source Core Rulebook pg. 470
    Trigger Your turn begins.
    You wait for the right moment to act. The rest of your turn doesn’t happen yet. Instead, you’re removed from the initiative order. You can return to the initiative order as a free action triggered by the end of any other creature’s turn. This permanently changes your initiative to the new position. You can’t use reactions until you return to the initiative order. If you Delay an entire round without returning to the initiative order, the actions from the Delayed turn are lost, your initiative doesn’t change, and your next turn occurs at your original position in the initiative order.

    When you Delay, any persistent damage or other negative effects that normally occur at the start or end of your turn occur immediately when you use the Delay action. Any beneficial effects that would end at any point during your turn also end. The GM might determine that other effects end when you Delay as well. Essentially, you can’t Delay to avoid negative consequences that would happen on your turn or to extend beneficial effects that would end on your turn.

    Drop Prone Single Action

    Move
    Source Core Rulebook pg. 470
    You fall prone

    Escape Single Action

    Attack
    Source Core Rulebook pg. 470
    You attempt to escape from being grabbed, immobilized, or restrained. Choose one creature, object, spell effect, hazard, or other impediment imposing any of those conditions on you. Attempt a check using your unarmed attack modifier against the DC of the effect. This is typically the Athletics DC of a creature grabbing you, the Thievery DC of a creature who tied you up, the spell DC for a spell effect, or the listed Escape DC of an object, hazard, or other impediment. You can attempt an Acrobatics or Athletics check instead of using your attack modifier if you choose (but this action still has the attack trait).

    Critical Success You get free and remove the grabbed, immobilized, and restrained conditions imposed by your chosen target. You can then Stride up to 5 feet.
    Success You get free and remove the grabbed, immobilized, and restrained conditions imposed by your chosen target.
    Critical Failure You don’t get free, and you can’t attempt to Escape again until your next turn.

    Interact Single Action

    Manipulate
    Source Core Rulebook pg. 470
    You use your hand or hands to manipulate an object or the terrain. You can grab an unattended or stored object, open a door, or produce some similar effect. You might have to attempt a skill check to determine if your Interact action was successful.

    Leap Single Action

    Move
    Source Core Rulebook pg. 470
    You take a careful, short jump. You can Leap up to 10 feet horizontally if your Speed is at least 15 feet, or up to 15 feet horizontally if your Speed is at least 30 feet. You land in the space where your Leap ends (meaning you can typically clear a 5-foot gap, or a 10-foot gap if your Speed is 30 feet or more).

    If you Leap vertically, you can move up to 3 feet vertically and 5 feet horizontally onto an elevated surface.

    Jumping a greater distance requires using the Athletics skill.

    Ready Two Actions

    Concentrate
    Source Core Rulebook pg. 470
    You prepare to use an action that will occur outside your turn. Choose a single action or free action you can use, and designate a trigger. Your turn then ends. If the trigger you designated occurs before the start of your next turn, you can use the chosen action as a reaction (provided you still meet the requirements to use it). You can’t Ready a free action that already has a trigger.

    If you have a multiple attack penalty and your readied action is an attack action, your readied attack takes the multiple attack penalty you had at the time you used Ready. This is one of the few times the multiple attack penalty applies when it’s not your turn.

    Release Free Action

    Manipulate
    Source Core Rulebook pg. 470
    You release something you’re holding in your hand or hands. This might mean dropping an item, removing one hand from your weapon while continuing to hold it in another hand, releasing a rope suspending a chandelier, or performing a similar action. Unlike most manipulate actions, Release does not trigger reactions that can be triggered by actions with the manipulate trait (such as Attack of Opportunity).

    If you want to prepare to Release something outside of your turn, use the Ready activity.

    Seek Single Action

    ConcentrateSecret
    Source Core Rulebook pg. 471
    You scan an area for signs of creatures or objects. If you’re looking for creatures, choose an area you’re scanning. If precision is necessary, the GM can have you select a 30-foot cone or a 15-foot burst within line of sight. You might take a penalty if you choose an area that’s far away.

    If you’re using Seek to search for objects (including secret doors and hazards), you search up to a 10-foot square adjacent to you. The GM might determine you need to Seek as an activity, taking more actions or even minutes or hours if you’re searching a particularly cluttered area.

    The GM attempts a single secret Perception check for you and compares the result to the Stealth DCs of any undetected or hidden creatures in the area or the DC to detect each object in the area (as determined by the GM or by someone Concealing the Object). A creature you detect might remain hidden, rather than becoming observed, if you’re using an imprecise sense or if an effect (such as invisibility) prevents the subject from being observed.

    Critical Success If you were searching for creatures, any undetected or hidden creature you critically succeeded against becomes observed by you. If you were searching for an object, you learn its location.
    Success If you were searching for creatures, any undetected creature you succeeded against becomes hidden from you instead of undetected, and any hidden creature you succeeded against becomes observed by you. If you were searching for an object, you learn its location or get a clue to its whereabouts, as determined by the GM.

    Sense Motive Single Action

    ConcentrateSecret
    Source Core Rulebook pg. 471
    You try to tell whether a creature’s behavior is abnormal. Choose one creature, and assess it for odd body language, signs of nervousness, and other indicators that it might be trying to deceive someone. The GM attempts a single secret Perception check for you and compares the result to the Deception DC of the creature, the DC of a spell af ecting the creature’s mental state, or another appropriate DC determined by the GM. You typically can’t try to Sense the Motive of the same creature again until the situation changes significantly.

    Critical Success You determine the creature’s true intentions and get a solid idea of any mental magic affecting it.
    Success You can tell whether the creature is behaving normally, but you don’t know its exact intentions or what magic might be affecting it.
    Failure You detect what a deceptive creature wants you to believe. If they’re not being deceptive, you believe they’re behaving normally.
    Critical Failure You get a false sense of the creature’s intentions.

    Stand Single Action

    Move
    Source Core Rulebook pg. 471
    You stand up from prone.

    Step Single Action

    Move
    Source Core Rulebook pg. 471
    Requirements Your Speed is at least 10 feet.
    You carefully move 5 feet. Unlike most types of movement, Stepping doesn’t trigger reactions, such as Attacks of Opportunity, that can be triggered by move actions or upon leaving or entering a square.

    You can’t Step into difficult terrain (page 475), and you can’t Step using a Speed other than your land Speed.

    Stride Single Action

    Move
    Source Core Rulebook pg. 471
    You move up to your Speed (page 463).

    Strike Single Action

    Attack
    Source Core Rulebook pg. 471
    You attack with a weapon you’re wielding or with an unarmed attack, targeting one creature within your reach (for a melee attack) or within range (for a ranged attack). Roll the attack roll for the weapon or unarmed attack you are using, and compare the result to the target creature’s AC to determine the effect. See Attack Rolls on page 446 and Damage on page 450 for details on calculating your attack and damage rolls.

    Take Cover Single Action

    Source Core Rulebook pg. 471
    Requirements You are benefiting from cover, are near a feature that allows you to take cover, or are prone.
    You press yourself against a wall or duck behind an obstacle to take better advantage of cover (page 477). If you would have standard cover, you instead gain greater cover, which provides a +4 circumstance bonus to AC; to Reflex saves against area effects; and to Stealth checks to Hide, Sneak, or otherwise avoid detection. Otherwise, you gain the benefits of standard cover (a +2 circumstance bonus instead). This lasts until you move from your current space, use an attack action, become unconscious, or end this effect as a free action.

    Specalty Basic Actions

    Source Core Rulebook pg. 472
    These actions are useful under specific circumstances. Some require you to have a special movement type (page 463).

    Arrest a Fall Reaction

    Source Core Rulebook pg. 472
    Trigger You fall.
    Requirements You have a fly Speed.
    You attempt an Acrobatics check to slow your fall. The DC is typically 15, but it might be higher due to air turbulence or other circumstances.

    Success You fall gently, taking no damage from the fall.

    Avert Gaze Single Action

    Source Core Rulebook pg. 472
    You avert your gaze from danger. You gain a +2 circumstance bonus to saves against visual abilities that require you to look at a creature or object, such as a medusa’s petrifying gaze. Your gaze remains averted until the start of your next turn.

    Burrow Single Action

    Move
    Source Core Rulebook pg. 472
    Requirements You have a burrow Speed.
    You dig your way through dirt, sand, or a similar loose material at a rate up to your burrow Speed. You can’t burrow through rock or other substances denser than dirt unless you have an ability that allows you to do so.

    Fly Single Action

    Move
    Source Core Rulebook pg. 472
    Requirements You have a fly Speed.
    You move through the air up to your fly Speed. Moving upward (straight up or diagonally) uses the rules for moving through difficult terrain. You can move straight down 10 feet for every 5 feet of movement you spend. If you Fly to the ground, you don’t take falling damage. You can use an action to Fly 0 feet to hover in place. If you’re airborne at the end of your turn and didn’t use a Fly action this round, you fall.

    Grab an Edge Reaction

    Manipulate
    Source Core Rulebook pg. 472
    Trigger You fall from or past an edge or handhold.
    Requirements Your hands are not tied behind your back or otherwise restrained
    When you fall of or past an edge or other handhold, you can try to grab it, potentially stopping your fall. You must succeed at a Ref ex save, usually at the Climb DC. If you grab the edge or handhold, you can then Climb up using Athletics.

    Critical Success You grab the edge or handhold, whether or not you have a hand free, typically by using a suitable held item to catch yourself (catching a battle axe on a ledge, for example). You still take damage from the distance fallen so far, but you treat the fall as though it were 30 feet shorter.
    Success If you have at least one hand free, you grab the edge or handhold, stopping your fall. You still take damage from the distance fallen so far, but you treat the fall as though it were 20 feet shorter. If you have no hands free, you continue to fall as if you had failed the check.
    Critical Failure You continue to fall, and if you’ve fallen 20 feet or more before you use this reaction, you take 10 bludgeoning damage from the impact for every 20 feet fallen.

    Mount Single Action

    Move
    Source Core Rulebook pg. 472
    Requirements You are adjacent to a creature that is at least one size larger than you and is willing to be your mount.
    You move onto the creature and ride it. If you’re already mounted, you can instead use this action to dismount, moving of the mount into a space adjacent to it.

    Point Out Single Action

    AuditoryManipulateVisual
    Source Core Rulebook pg. 472
    Requirements A creature is undetected by one or more of your allies but isn’t undetected by you.
    You indicate a creature that you can see to one or more allies, gesturing in a direction and describing the distance verbally. That creature is hidden to your allies, rather than undetected (page 466). This works only for allies who can see you and are in a position where they could potentially detect the target. If your allies can’t hear or understand you, they must succeed at a Perception check against the creature’s Stealth DC or they misunderstand and believe the target is in a different location.

    Raise a Shield Single Action

    Source Core Rulebook pg. 472
    Requirements You are wielding a shield.
    You position your shield to protect yourself. When you have Raised a Shield, you gain its listed circumstance bonus to AC. Your shield remains raised until the start of your next turn.

    Activities in Encounters

    Source Core Rulebook pg. 472
    Activities that take longer than a turn can’t normally be performed during an encounter. Spells with a casting time of 1 minute or more are a common example of this, as are several skill actions. When you commit to an activity during your turn in an encounter, you commit to spending all of the actions it requires. If the activity gets interrupted partway through, you lose all of the actions you would have spent on that activity. Activities are described in full on page 461.

    Reactions in Encounters

    Source Core Rulebook pg. 472
    Your reactions let you respond immediately to what’s happening around you. The GM determines whether you can use reactions before your first turn begins, depending on the situation in which the encounter happens.

    Once your first turn begins, you gain your actions and reaction. You can use 1 reaction per round. You can use a reaction on anyone’s turn (including your own), but only when its trigger occurs. If you don’t use your reaction, you lose it at the start of your next turn, though you typically then gain a reaction at the start of that turn.

    Some reactions are specifically meant to be used in combat and can change how the battle plays out drastically. One example of such a reaction is Attack of Opportunity, which fighters gain at 1st level.

    Attack of Opportunity Reaction

    Source Core Rulebook pg. 142
    Trigger A creature within your reach uses a manipulate action or a move action, makes a ranged attack, or leaves a square during a move action it’s using.
    You lash out at a foe that leaves an opening. Make a melee Strike against the triggering creature. If your attack is a critical hit and the trigger was a manipulate action, you disrupt that action. This Strike doesn’t count toward your multiple attack penalty, and your multiple attack penalty doesn’t apply to this Strike.This reaction lets you make a melee Strike if a creature within reach uses a manipulate or move action, makes a ranged attack, or leaves a square during a move action. The Triggering Moves diagram on page 474 illustrates examples of movements that might trigger an Attack of Opportunity from a creature without reach and one with reach.

    You’ll notice this reaction allows you to use a modified basic action, a Strike. This follows the rules on subordinate actions found on page 462. Because your Attack of Opportunity takes place outside of your turn, the attack roll doesn’t incur a multiple attack penalty.

    Movement in Encounters

    Source Core Rulebook pg. 473
    Your movement during encounter mode depends on the actions and other abilities you use. Whether you Stride, Step, Swim, or Climb, the maximum distance you can move is based on your Speed. Certain feats or magic items can grant you other movement types, allowing you to swiftly burrow, climb, fly, or swim (page 463).

    When the rules refer to a “movement cost” or “spending movement,” they are describing how many feet of your Speed you must use to move from one point to another. Normally, movement costs 5 feet per square when you’re moving on a grid, or it costs the number of feet you move if you’re not using a grid. However, sometimes it’s harder to move a certain distance due to difficult terrain (page 475) or other factors. In such a case, you might have to spend a different amount of movement to move from one place to another. For example, a form of movement might require 10 feet of movement to move 1 square, and moving through some types of terrain costs an extra 5 feet of movement per square.

    Grid Movement

    Source Core Rulebook pg. 473
    If an encounter involves combat, it’s often a good idea to track the movement and relative position of the participants using a Pathfinder Flip-Mat, Flip-Tiles, or some other form of grid to display the terrain, and miniatures to represent the combatants. When a character moves on a grid, every 1-inch square of the play area is 5 feet across in the game world. Hence, a creature moving in a straight line spends 5 feet of its movement for every map square traveled.

    Because moving diagonally covers more ground, you count that movement differently. The first square of diagonal movement you make in a turn counts as 5 feet, but the second counts as 10 feet, and your count thereafter alternates between the two. For example, as you move across 4 squares diagonally, you would count 5 feet, then 10, then 5, and then 10, for a total of 30 feet. You track your total diagonal movement across all your movement during your turn, but reset your count at the end of your turn.

    Size, Space, and Reach

    Source Core Rulebook pg. 473
    Creatures and objects of different sizes occupy different amounts of space. The sizes and the spaces they each take up on a grid are listed in Table 9–1: Size and Reach (page 474). Table 9–1 also lists the typical reach for creatures of each size, for both tall creatures (most bipeds) and long creatures (most quadrupeds). See page 455 for more about reach.

    The Space entry lists how many feet on a side a creature’s space is, so a Large creature fills a 10-foot-by-10-foot space (4 squares on the grid). Sometimes part of a creature extends beyond its space, such as if a giant octopus is grabbing you with its tentacles. In that case, the GM will usually allow attacking the extended portion, even if you can’t reach the main creature. A Small or larger creature or object takes up at least 1 square on a grid, and creatures of these sizes can’t usually share spaces except in situations like a character riding a mount. Rules for moving through other creatures’ spaces appear below.

    Table 9-1: Size and Reach

    SizeSpaceReach (Tall)Reach (Long)
    TinyLess than 5 feet0 feet0 feet
    Small5 feet5 feet5 feet
    Medium5 feet5 feet5 feet
    Large10 feet10 feet5 feet
    Huge15 feet15 feet10 feet
    Gargantuan20 feet or more20 feet15 feet


    Multiple Tiny creatures can occupy the same square. At least four can fit in a single square, though the GM might determine that even more can fit. Tiny creatures can occupy a space occupied by a larger creature as well, and if their reach is 0 feet, they must do so in order to attack.

    Move Actions that Trigger Reactions

    Source Core Rulebook pg. 474
    Some reactions and free actions are triggered by a creature using an action with the move trait. The most notable example is Attack of Opportunity. Actions with the move trait can trigger reactions or free actions throughout the course of the distance traveled. Each time you exit a square (or move 5 feet if not using a grid) within a creature’s reach, your movement triggers those reactions and free actions (although no more than once per move action for a given reacting creature). If you use a move action but don’t move out of a square, the trigger instead happens at the end of that action or ability.

    Some actions, such as Step, specifically state they don’t trigger reactions or free actions based on movement.

    Moving Through a Creature's Space

    Source Core Rulebook pg. 474
    You can move through the space of a willing creature. If you want to move through an unwilling creature’s space, you can Tumble Through that creature’s space using Acrobatics. You can’t end your turn in a square occupied by another creature, though you can end a move action in its square provided that you immediately use another move action to leave that square. If two creatures end up in the same square by accident, the GM determines which one is forced out of the square (or whether one falls prone).

    Prone and Incapacitated Creatures

    Source Core Rulebook pg. 474
    You can share a space with a prone creature if that creature is willing, unconscious, or dead and if it is your size or smaller. The GM might allow you to climb atop the corpse or unconscious body of a larger creature in some situations. A prone creature can’t stand up while someone else occupies its space, but it can Crawl to a space where it’s able to stand, or it can attempt to Shove the other creature out of the way.

    Creatures of Different Sizes

    Source Core Rulebook pg. 475
    In most cases, you can move through the space of a creature at least three sizes larger than you (Table 9-1). This means a Medium creature can move through the space of a Gargantuan creature and a Small creature can move through the space of a Huge creature. Likewise, a bigger creature can move through the space of a creature three sizes smaller than itself or smaller. You still can’t end your movement in a space occupied by a creature.

    Tiny creatures are an exception. They can move through creatures’ spaces and can even end their movement there.

    Objects

    Source Core Rulebook pg. 475
    Because objects aren’t as mobile as creatures are, they’re more likely to fill a space. This means you can’t always move through their spaces like you might move through a space occupied by a creature. You might be able to occupy the same square as a statue of your size, but not a wide column. The GM determines whether you can move into an object’s square normally, whether special rules apply, or if you are unable to move into the square at all.

    Forced Movement

    Source Core Rulebook pg. 475
    When an effect forces you to move, or if you start falling, the distance you move is defined by the effect that moved you, not by your Speed. Because you’re not acting to move, this doesn’t trigger reactions that are triggered by movement.

    If forced movement would move you into a space you can’t occupy—because objects are in the way or because you lack the movement type needed to reach it, for example—you stop moving in the last space you can occupy. Usually the creature or effect forcing the movement chooses the path the victim takes. If you’re pushed or pulled, you can usually be moved through hazardous terrain, pushed off a ledge, or the like. Abilities that reposition you in some other way can’t put you in such dangerous places unless they specify otherwise. In all cases, the GM makes the final call if there’s doubt on where forced movement can move a creature.

    Terrain

    Source Core Rulebook pg. 475
    Several types of terrain can complicate your movement by slowing you down, damaging you, or endangering you.

    Difficult Terrain

    Source Core Rulebook pg. 475
    Difficult terrain is any terrain that impedes your movement, ranging from particularly rough or unstable surfaces to thick ground cover and countless other impediments. Moving into a square of difficult terrain (or moving 5 feet into or within an area of difficult terrain, if you’re not using a grid) costs an extra 5 feet of movement. Moving into a square of greater difficult terrain instead costs 10 additional feet of movement. This additional cost is not increased when moving diagonally. You can’t Step into difficult terrain.

    Movement you make while you are jumping ignores the terrain you’re jumping over. Some abilities (such as flight or being incorporeal) allow you to avoid the movement reduction from some types of difficult terrain. Certain other abilities let you ignore difficult terrain on foot; such an ability also allows you to move through greater difficult terrain at the normal movement cost as for difficult terrain, though it wouldn’t let you ignore greater difficult terrain unless the ability specifies otherwise.

    Hazardous Terrain

    Source Core Rulebook pg. 476
    Hazardous terrain damages you whenever you move through it. An acid pool and a pit of burning embers are both examples of hazardous terrain. The amount and type of damage depend on the specific hazardous terrain.

    Narrow Surfaces

    Source Core Rulebook pg. 476
    A narrow surface is so precariously thin that you need to Balance (see Acrobatics) or risk falling. Even on a success, you are flat-footed on a narrow surface. Each time you are hit by an attack or fail a save on a narrow surface, you must succeed at a Reflex save (with the same DC as the Acrobatics check to Balance) or fall.

    Uneven Ground

    Source Core Rulebook pg. 476
    Uneven ground is an area unsteady enough that you need to Balance (see Acrobatics) or risk falling prone and possibly injuring yourself, depending on the specifics of the uneven ground. You are flat-footed on uneven ground. Each time you are hit by an attack or fail a save on uneven ground, you must succeed at a Reflex save (with the same DC as the Acrobatics check to Balance) or fall prone.

    Inclines

    Source Core Rulebook pg. 476
    An incline is an area so steep that you need to Climb using the Athletics skill in order to progress upward. You’re flat-footed when Climbing an incline.

    Flanking

    Source Core Rulebook pg. 476
    When you and an ally are flanking a foe, it has a harder time defending against you. A creature is flat-footed (taking a –2 circumstance penalty to AC) to creatures that are flanking it.

    To flank a foe, you and your ally must be on opposites sides or corners of the creature. A line drawn between the center of your space and the center of your ally’s space must pass through opposite sides or opposite corners of the foe’s space. Additionally, both you and the ally have to be able to act, must be wielding melee weapons or able to make an unarmed attack, can’t be under any effects that prevent you from attacking, and must have the enemy within reach. If you are wielding a reach weapon, you use your reach with that weapon for this purpose.

    Cover

    Source Core Rulebook pg. 477
    When you’re behind an obstacle that could block weapons, guard you against explosions, and make you harder to detect, you’re behind cover. Standard cover gives you a +2 circumstance bonus to AC, to Reflex saves against area effects, and to Stealth checks to Hide, Sneak, or otherwise avoid detection. You can increase this to greater cover using the Take Cover basic action, increasing the circumstance bonus to +4. If cover is especially light, typically when it’s provided by a creature, you have lesser cover, which grants a +1 circumstance bonus to AC. A creature with standard cover or greater cover can attempt to use Stealth to Hide, but lesser cover isn’t sufficient.

    Cover is relative, so you might simultaneously have cover against one creature and not another. Cover applies only if your path to the target is partially blocked. If a creature is entirely behind a wall or the like, you don’t have line of effect and typically can’t target it at all.

    Usually, the GM can quickly decide whether your target has cover. If you’re uncertain or need to be more precise, draw a line from the center of your space to the center of the target’s space. If that line passes through any terrain or object that would block the effect, the target has standard cover (or greater cover if the obstruction is extreme or the target has Taken Cover). If the line passes through a creature instead, the target has lesser cover. When measuring cover against an area effect, draw the line from the effect’s point of origin to the center of the creature’s space.

    Cover and Large Creatures

    Source Core Rulebook pg. 477
    If a creature between you and a target is two or more sizes larger than both you and your target, that creature’s space blocks the effect enough to provide standard cover instead of lesser cover. The GM might determine that a creature doesn’t gain cover from terrain that it’s significantly larger than. For example, a Huge dragon probably wouldn’t receive any benefit from being behind a 1-foot-wide pillar.

    Special Circumstances

    Source Core Rulebook pg. 477
    Your GM might allow you to overcome your target’s cover in some situations. If you’re right next to an arrow slit, you can shoot without penalty, but you have greater cover against someone shooting back at you from far away. Your GM might let you reduce or negate cover by leaning around a corner to shoot or the like. This usually takes an action to set up, and the GM might measure cover from an edge or corner of your space instead of your center.

    Special Battles

    Source Core Rulebook pg. 477
    Sometimes fights occur while the characters are atop mounts or when the PCs take to the sky or seas.

    Mounted Combat

    Source Core Rulebook pg. 478
    You can ride some creatures into combat. As noted in the Mount specialty basic action (page 472), your mount needs to be at least one size larger than you and willing. Your mount acts on your initiative. You must use the Command an Animal action to get your mount to spend its actions. If you don’t, the animal wastes its actions. If you have the Ride general feat, you succeed automatically when you Command an Animal that’s your mount.

    For example, if you are mounted on a horse and you make three attacks, your horse would remain stationary since you didn’t command it. If you instead spent your first action to Command an Animal and succeeded, you could get your mount to Stride. You could spend your next action to attack or to command the horse to attack, but not both.

    Mounted Attacks

    Source Core Rulebook pg. 478
    You and your mount fight as a unit. Consequently, you share a multiple attack penalty. For example, if you Strike and then Command an Animal to have your mount Strike, your mount’s attack takes a –5 multiple attack penalty.

    You occupy every square of your mount’s space for the purpose of making your attacks. If you were Medium and on a Large mount, you could attack a creature on one side of your mount, then attack on the opposite side with your next action. If you have a longer reach, the distance depends partly on the size of your mount. On a Medium or smaller mount, use your normal reach. On a Large or Huge mount, you can attack any square adjacent to the mount if you have 5- or 10-foot reach, or any square within 10 feet of the mount (including diagonally) if you have 15-foot reach.

    Mounted Defenses

    Source Core Rulebook pg. 478
    When you’re mounted, attackers can target either you or your mount. Anything that affects multiple creatures (such as an area) affects both of you as long as you’re both in the area. You are in an attacker’s reach or range if any square of your mount is within reach or range. Because your mount is larger than you and you share its space, you have lesser cover against attacks targeting you when you’re mounted if the mount would be in the way.

    Because you can’t move your body as freely while you’re riding a mount, you take a –2 circumstance penalty to Reflex saves while mounted. Additionally, the only move action you can use is the Mount action to dismount.

    Aerial Combat

    Source Core Rulebook pg. 478
    Many monsters can fly, and PCs can use spells and items to gain the ability to fly. Flying creatures have to use the Fly action (page 472) to move through the air. Performing an especially tricky maneuver—such as trying to reverse course 180 degrees or fly through a narrow gap—might require using Acrobatics to Maneuver in Flight. Creatures might fall from the sky, using the falling rules. At the GM’s discretion, some ground-based actions might not work in the air. For instance, a flying creature couldn’t Leap.

    Aquatic Combat

    Source Core Rulebook pg. 478
    Use these rules for battles in water or underwater:
    • You’re flat-footed unless you have a swim Speed.
    • You gain resistance 5 to acid and fire.
    • You take a –2 circumstance penalty to melee slashing or bludgeoning attacks that pass through water.
    • Ranged attacks that deal bludgeoning or slashing damage automatically miss if the attacker or target is underwater, and piercing ranged attacks made by an underwater creature or against an underwater target have their range increments halved.
    • You can’t cast fire spells or use actions with the fire trait underwater.
    • At the GM’s discretion, some ground-based actions might not work underwater or while floating.

    Drowning and Suffocation

    Source Core Rulebook pg. 478
    You can hold your breath for a number of rounds equal to 5 + your Constitution modifier. Reduce your remaining air by 1 round at the end of each of your turns, or by 2 if you attacked or cast any spells that turn. You also lose 1 round worth of air each time you are critically hit or critically fail a save against a damaging effect. If you speak (including casting spells with verbal components or activating items with command components) you lose all remaining air.

    When you run out of air, you fall unconscious and start suffocating. You can’t recover from being unconscious and must attempt a DC 20 Fortitude save at the end of each of your turns. On a failure, you take 1d10 damage, and on a critical failure, you die. On each check after the first, the DC increases by 5 and the damage by 1d10; these increases are cumulative. Once your access to air is restored, you stop suffocating and are no longer unconscious (unless you’re at 0 Hit Points).