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SURPRISE
The DM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the DM compares the Stealth checks of anyone hiding with the passive Perception score of each creature on the opposing side. Any character or monster that doesn't notice a threat is surprised at the start of the encounter. If you're surprised, you can't move or take an action on your first turn of the combat, and you can't take a reaction until that turn ends. A member of a group can be surprised even if the other members aren't.

THE ACTION FLOW
Characters and monsters act when it makes narrative sense for them to to so. The DM is responsible for tracking who has already acted within the current round, ensuring no extra or missing turn occurs. The DM also aims to alternate turns between PCs and monsters, prioritising the combatant that is central to the current scene. If there is no clear central character the DM can always ask the players who wants to go next. Players retain the ability to object the DM's chosen order, but the DM has the final say.
If there is a doubt about which of two creatures should act next, they can roll a Dexterity check to determine who goes first.

YOUR TURN
On your turn, you can move a distance up to your speed and take one action. You decide whether to move first or take your action first. Your speed — sometimes called your walking speed — is noted on your character sheet. The most common actions you can take are described in the "Actions in Combat" section later in this chapter.
The "Movement and Position" section later in this chapter gives the rules for your move.
You can forgo moving, taking an action, or doing anything at all on your turn. If you can't decide what to do on your turn, consider taking the Dodge or Ready action, as described in "Actions in Combat."

OTHER ACTIVITY IN YOUR TURN
Your turn can include a variety of flourishes that require neither your action nor your move.
You can communicate however you are able, through brief utterances and gestures, as you take your turn.
You can also interact with one object or feature of the environment for free, during either your move or your action. For example, you could open a door during your move as you stride toward a foe, or you could draw your weapon as part of the same action you use to attack.
If you want to interact with a second object, you need to use your action. Some magic items and other special objects always require an action to use, as stated in their descriptions.
The DM might require you to use an action for any of these activities when it needs special care or when it presents an unusual obstacle. For instance, the DM could reasonably expect you to use an action to open a stuck door or turn a crank to lower a drawbridge.
Here are a few examples of the sorts of thing you can do in tandem with your movement and action:
Interruptions
A character with the Combat Reflexes skill can interrupt another character's turn if:
A character that interrupts another character's turn can make a single melee attack against the other character. This attack interrupts the other character's movement or action, occurring right before the other character leaves their reach or completes their action. Doing so uses up the character's action for this round. After the action is resolved, the acting character completes their turn, and the interrupting character is left with just their movement.
A character with the Counterpsell skill can interrupt another character's turn to counterspell a spell that is being cast. They roll a spellcraft check to see if they know the spell, and can then proceed to counterspell as explained in the "Counterspelling" section. Doing so uses up the character's action for this round. After the action is resolved, the acting character completes their turn, and the interrupting character is left with just their movement.

MOVEMENT AND POSITION
In combat, characters and monsters are in constant motion, often using movement and position to gain the upper hand.
On your turn, you can move a distance up to your speed. You can use as much or as little of your speed as you like on your turn, following the rules here.
Your movement can include jumping, climbing, and swimming. These different modes of movement can be combined with walking, or they can constitute your entire move. However you're moving, you deduct the distance of each part of your move from your speed until it is used up or until you are done moving.
Breaking Up Your Move
You can break up your movement on your turn, using some of your speed before and after your action. For example, if you have a speed of 30 feet, you can move 10 feet, take your action, and then move 20 feet.
Moving between Attacks
If you take an action that includes more than one weapon attack, you can break up your movement even further by moving between those attacks. For example, a fighter who can make two attacks with the Extra Attack feature and who has a speed of 25 feet could move 10 feet, make an attack, move 15 feet, and then attack again.
Using Different Speeds
If you have more than one speed, such as your walking speed and a flying speed, you can switch back and forth between your speeds during your move. Whenever you switch, subtract the distance you've already moved from the new speed. The result determines how much farther you can move. If the result is 0 or less, you can't use the new speed during the current move.
For example, if you have a speed of 30 and a flying speed of 60 because a wizard cast the fly spell on you, you could fly 20 feet, then walk 10 feet, and then leap into the air to fly 30 feet more.
Difficult Terrain
Combat rarely takes place in bare rooms or on featureless plains. Boulder-strewn caverns, briar-choked forests, treacherous staircases — the setting of a typical fight contains difficult terrain.
Every foot of movement in difficult terrain costs 1 extra foot. This rule is true even if multiple things in a space count as difficult terrain.
Low furniture, rubble, undergrowth, steep stairs, snow, and shallow bogs are examples of difficult terrain. The space of another creature, whether hostile or not, also counts as difficult terrain.

BEING PRONE
Combatants often find themselves lying on the ground, either because they are knocked down or because they throw themselves down. In the game, they are prone.
You can drop prone without using any of your speed. Standing up takes more effort; doing so costs an amount of movement equal to half your speed. For example, if your speed is 30 feet, you must spend 15 feet of movement to stand up. You can't stand up if you don't have enough movement left or if your speed is 0.
To move while prone, you must crawl or use magic such as teleportation. Every foot of movement while crawling costs 1 extra foot. Crawling 1 foot in difficult terrain, therefore, costs 3 feet of movement.

MOVING AROUND OTHER CREATURES
You can move through a nonhostile creature's space. In contrast, you can move through a hostile creature's space only if the creature is at least two sizes larger or smaller than you. Remember that another creature's space is difficult terrain for you.
Whether a creature is a friend or an enemy, you can't willingly end your move in its space.
If you leave a hostile creature's reach during your move, they may be able to interrupt your turn to attack you.

FLYING MOVEMENT
Flying creatures enjoy many benefits of mobility, but they must also deal with the danger of falling. If a flying creature is knocked prone, has its speed reduced to 0, or is otherwise deprived of the ability to move, the creature falls, unless it has the ability to hover or it is being held aloft by magic, such as by the fly spell.

CREATURE SIZE
Each creature takes up a different amount of space. The Size Categories table shows how much space a creature of a particular size controls in combat. Objects sometimes use the same size categories.
Size Categories
Size Space
Tiny 2 1/2 by 2 1/2 ft
Small 5 by 5 ft
Medium 5 by 5 ft
Large 10 by 10 ft
Huge 15 by 15 ft
Gargantuan 20 by 20 ft or larger

SPACE
A creature's space is the area in feet that it effectively controls in combat, not an expression of its physical dimensions. A typical Medium creature isn't 5 feet wide, for example, but it does control a space that wide. If a Medium hobgoblin stands in a 5-foot-wide doorway, other creatures can't get through unless the hobgoblin lets them.
A creature's space also reflects the area it needs to fight effectively. For that reason, there's a limit to the number of creatures that can surround another creature in combat. Assuming Medium combatants, eight creatures can fit in a 5-foot radius around another one.
Because larger creatures take up more space, fewer of them can surround a creature. If five Large creatures crow d around a Medium or smaller one, there's little room for anyone else. In contrast, as many as twenty Medium creatures can surround a Gargantuan one.
Squeezing into a Smaller Space
A creature can squeeze through a space that is large enough for a creature one size smaller than it. Thus, a Large creature can squeeze through a passage that's only 5 feet wide. While squeezing through a space, a creature must spend 1 extra foot for every foot it moves there, and it has disadvantage on attack rolls and Dexterity saving throws. Attack rolls against the creature have advantage while it's in the smaller space.

HIDING
When you try to hide, make a Stealth check. Until you are discovered or you stop hiding, that check's total is contested by the Perception check of any creature that actively searches for signs of your presence.
You can't hide from a creature that can see you, and if you make noise (such as shouting a warning or knocking over a vase), you give away your position. An invisible creature can't be seen, so it can always try to hide. Signs of its passage might still be noticed, however, and it still has to stay quiet.
In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you. However, under certain circumstances, the Dungeon Master might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain advantage on an attack before you are seen.
Passive Perception. When you hide, there's a chance someone will notice you even if they aren't searching. To determine whether such a creature notices you, the DM compares your Stealth check with that creature's passive Perception score, which equals 10 + the creature's Perception skill.
For example, if character has a Percetion skill of 4 and has a Wisdom of 15 (a +2 modifier), he or she has a passive Perception of 16.
What Can You See? One of the main factors in determining whether you can find a hidden creature or object is how well you can see in an area, which might be lightly or heavily obscured.
Unseen Attackers and Targets
Combatants often try to escape their foes' notice by hiding, casting the invisibility spell, or lurking in darkness.
When you attack a target that you can't see, you have 50% miss chance on the attack roll. This is true whether you're guessing the target's location or you're targeting a creature you can hear but not see. If the target isn't in the location you targeted, you automatically miss, but the DM typically just says that the attack missed, not whether you guessed the target's location correctly.
When a creature can't see you, you have +5 bonus on attack rolls against it.
If you are hidden — both unseen and unheard — when you make an attack, you give away your location when the attack hits or misses.

ACTIONS IN COMBAT
Improvising an Action
Your character can do things not covered by the actions in this chapter, such as breaking down doors, intimidating enemies, sensing weaknesses in magical defenses, or calling for a parley with a foe. The only limits to the actions you can attempt are your imagination and your character's ability scores.
When you describe an action not detailed elsewhere in the rules, the DM tells you whether that action is possible and what kind of roll you need to make, if any, to determine success or failure.

When you take your action on your turn, you can take one of the actions presented here, an action you gained from a skill, or an action that you improvise. When you describe an action not detailed elsewhere in the rules, the DM tells you whether that action is possible and what kind of roll you need to make, if any, to determine success or failure.
Attack
The most common action to take in combat is the Attack action, whether you are swinging a sword, firing an arrow from a bow, or brawling with your fists.
With this action, you make one melee or ranged attack. See the "Making an Attack" section for the rules that govern attacks.
Depending on your skills and the weapons you are wielding, you might be able to make more than an attack. All the attacks you can make are part of the Attack action.
Cast a Spell
Spellcasters have access to spells and can use them to great effect in combat. Each spell has a casting time, which specifies whether the caster must use an action, minutes, or even hours to cast the spell. Casting a spell is, therefore, not necessarily an action. Most spells do have a casting time of 1 action, so a spellcaster often uses his or her action in combat to cast such a spell. Some rare spells, such as feather fall or shield have a casting time of an immediate action, which means that can be cast also out of your turn, for example while you are being attacked.
Touch Spells in Combat: Many spells have a range of touch. You can automatically touch one friend or use the spell on yourself, but to touch an opponent, you must succeed on an attack roll.
Touch Attacks: Touching an opponent with a touch spell is considered to be an armed attack. Touch attacks come in two types: melee touch attacks and ranged touch attacks. You can score critical hits with either type of attack. Your opponent's AC against a touch attack does not include any armor bonus, shield bonus, or natural armor bonus. His size modifier, Dexterity modifier, and deflection bonus (if any) all apply normally.
Dash
When you take the Dash action, you gain extra movement for the current turn. The increase equals your speed, after applying any modifiers. With a speed of 30 feet, for example, you can move up to 60 feet on your turn if you dash.
Any increase or decrease to your speed changes this additional movement by the same amount. If your speed of 30 feet is reduced to 15 feet, for instance, you can move up to 30 feet this turn if you dash.
Disengage
If you take the Disengage action, your movement does not leave you vulnearble to attacks, even if you move away from an enemy.
Dodge
When you take the Dodge action, you focus entirely on avoiding attacks. Until the start of your next turn, you receive a +5 bonus to your Dodge and Reflex skill if you can see the attacker, wether it is a creature or an effect. You lose this benefit if you are incapacitated or if your speed drops to 0.
Help
You can lend your aid to another creature in the completion of a task. When you take the Help action, the creature you aid gains a +5 bonus on the next skill check it makes to perform the task you are helping with, provided that it makes the check before the start of your next turn.
Alternatively, you can aid a friendly creature in attacking a creature within 5 feet of you. You feint, distract the target, or in some other way team up to make your ally's attack more effective. If your ally attacks the target before your next turn, the first attack roll is made with a +5 bonus.
Ready
Errata
"You have until the start of your next turn to use a readied action." Player's Handbook Errata

Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn so that you can act later in the round using your reaction. First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. Examples include "If the cultist steps on the trapdoor, I'll pull the lever that opens it," and "If the goblin steps next to me, I move away."
When the trigger occurs, you can either take the action you readied right after the trigger finishes or ignore the trigger.
Search
When you take the Search action, you devote your attention to finding something. Depending on the nature of your search, the DM might have you make a Perception check or an Investigation check.
Use an Object
You normally interact with an object while doing something else, such as when you draw a sword as part of an attack. When an object requires your action for its use, you take the Use an Object action. This action is also useful when you want to interact with more than one object on your turn.

MAKING AN ATTACK
Whether you're striking with a melee weapon, firing a weapon at range, or making an attack roll as part of a spell, an attack has a simple structure.
  1. Choose a target. Pick a target within your attack's range: a creature, an object, or a location.
  2. Determine modifiers. The DM determines whether the target has cover and whether you have any bonus or malus against the target. In addition, spells, special abilities, and other effects can apply penalties or bonuses to your attack roll.
  3. Resolve the attack. You make the attack roll. On a hit, you roll damage, unless the particular attack has rules that specify otherwise. Some attacks cause special effects in addition to or instead of damage.
If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making a roll against AC or Reflex or Fortitude or Will, you're making an attack.
Attack Rolls
When you make an attack, your attack roll determines whether the attack hits or misses. To make an attack roll, roll a d20 and add the appropriate skill modifiers. If the total of the roll plus modifiers equals or exceeds the target's Armor Class (AC), Reflex, Fortitude or Will, the attack hits.
Modifiers to the Roll
When a character makes an attack roll, the two most common modifiers to the roll are an ability modifier and the character's skill in the weapon used to make the attack. When a monster makes an attack roll, it uses whatever modifier is provided in its stat block.
Ability Modifier. The ability modifier used for a melee weapon attack is Strength, and the ability modifier used for a ranged weapon attack is Dexterity. Weapons that have the finesse or thrown property break this rule.
Some spells also require an attack roll. With melee weapons, when you use them two-handed, you add 1.5 times your strength modifier, rounded down. While useing off-hand weapons, you only add half your strength or dexterity modifier, rounded down.
Rolling 1 or 20
Sometimes fate blesses or curses a combatant, causing the novice to hit and the veteran to miss.
If the d20 roll for an attack is a 20, the attack hits regardless of any modifiers or the target's defence. In addition, the attack is a critical hit, as explained later in this chapter.
If the d20 roll for an attack is a 1, the attack misses regardless of any modifiers or the target's AC.
Unseen Attackers and Targets
Combatants often try to escape their foes' notice by hiding, casting the invisibility spell, or lurking in darkness.
When you attack a target that you can't see, you have -5 on the attack roll. This is true whether you're guessing the target's location or you're targeting a creature you can hear but not see. If the target isn't in the location you targeted, you automatically miss, but the DM typically just says that the attack missed, not whether you guessed the target's location correctly.
When a creature can't see you, you have a +5 bonus on attack rolls against it.
If you are hidden — both unseen and unheard — when you make an attack, you give away your location when the attack hits or misses.
Ranged Attacks
When you make a ranged attack, you fire a bow or a crossbow, hurl a handaxe, or otherwise send projectiles to strike a foe at a distance. A monster might shoot spines from its tail. Many spells also involve making a ranged attack.
Range
You can make ranged attacks only against targets within a specified range.
If a ranged attack, such as one made with a spell, has a single range, you can't attack a target beyond this range.
Some ranged attacks, such as those made with a longbow or a shortbow, have two ranges. The smaller number is the normal range, and the larger number is the long range. Your attack roll has -5 malus when your target is beyond normal range, and you can't attack a target beyond the long range.
Ranged Attacks in Close Combat
Aiming a ranged attack is more difficult when a foe is next to you. When you make a ranged attack with a weapon, a spell, or some other means, if you are within 5 feet of a hostile creature who can see you and who isn't incapacitated you leave room for receiving an attack. If a creature decides to attack you this way, they use their action for this round.
Melee Attacks
Used in hand-to-hand combat, a melee attack allows you to attack a foe within your reach. A melee attack typically uses a handheld weapon such as a sword, a warhammer, or an axe. A typical monster makes a melee attack when it strikes with its claws, horns, teeth, tentacles, or other body part. A few spells also involve making a melee attack.
Most creatures have a 5-foot reach and can thus attack targets within 5 feet of them when making a melee attack. Certain creatures (typically those larger than Medium) have melee attacks with a greater reach than 5 feet, as noted in their descriptions.
Instead of using a weapon to make a melee weapon attack, you can use an unarmed strike: a punch, kick, head-butt, or similar forceful blow (none of which count as weapons). On a hit, unless you have the unarmed combat skill,an unarmed strike deals bludgeoning damage equal to 1 + your Strength modifier.
Two-Weapon Fighting
When you take the Attack action and attack with a melee weapon that you're holding in the main hand, you can also attack with a different light melee weapon that you're holding in the off-hand. You only add half your ability modifier to the damage of the off-hand attack rounded down, unless that modifier is negative, in which case you add it all.
If either weapon has the thrown property, you can throw the weapon, instead of making a melee attack with it.
Contests in Combat
Battle often involves pitting your prowess against that of your foe. Such a challenge is represented by a contest. This section includes the most common contests that require an action in combat: grappling and shoving a creature. The DM can use these contests as models for improvising others.
Grappling
When you want to grab a creature or wrestle with it, you can use the Attack action to make a special melee attack, a grapple. If you're able to make multiple attacks with the Attack action, this attack replaces one of them.
The target of your grapple must be no more than one size larger than you, and it must be within your reach. Using at least one free hand, you try to seize the target by making a grapple check, an Athletics check contested by the target's Athletics or Acrobatics check (the target chooses the ability to use). If you succeed, the target is grappled. The condition specifies the things that end it, and you can release the target whenever you like (no action required).
Escaping a Grapple.
A grappled creature can use its action to escape. To do so, it must succeed on an Athletics or Acrobatics check contested by your Athletics check.
Moving a Grappled Creature.
When you move, you can drag or carry the grappled creature with you, but your speed is halved, unless the creature is two or more sizes smaller than you.
Shoving a Creature
Using the Attack action, you can make a special melee attack to shove a creature, either to knock it prone or push it away from you. If you're able to make multiple attacks with the Attack action, this attack replaces one of them.
The target of your shove must be no more than one size larger than you, and it must be within your reach. You make an Athletics check contested by the target's Athletics or Acrobatics check (the target chooses the ability to use). If you win the contest, you either knock the target prone or push it 5 feet away from you.

DEFENDING AGAINST ATTACKS
In this game, the players roll all the dice. That means whenever your character is targeted by a weapon, a spell, or any harmful effect, you roll to defend yourself. The DM never rolls against your defences — instead, you roll to avoid or resist the attack.
  1. Determine the threat. When an enemy targets you, the DM tells you which defence is being challenged: AC (to avoid a weapon strike), Reflex (to dodge area effects), Fortitude (to resist physical harm), or Will (to resist mental effects).
  2. Apply modifiers. The DM tells you if there are any bonuses or penalties to the roll from conditions, spells, cover, or other effects.
  3. Resolve the defence. You roll a d20 and add your defence bonus. If your total equals or exceeds the attacker’s bonus (or a fixed difficulty), you successfully resist the attack. Otherwise, the attack hits you and its effects apply.
If you're being directly targeted by any harmful effect that would normally require the DM to roll against your defences, you roll instead.
Defence Rolls
There are four main defences in the game: Each defence has a fixed bonus determined by your character's stats, items, and abilities. Unlike skill rolls, no skill modifier is added to defence rolls unless a specific trait says so.
Touch Attacks: Some attacks disregard armor, including shields and natural armor. In these cases, the attacker makes a touch attack roll (either ranged or melee). When you are the target of a touch attack, your AC doesn't include any armor bonus, shield bonus, or natural armor bonus. All other modifiers, such as your size modifier, Dexterity modifier, and deflection bonus (if any) apply normally.


Critical Hits and Fumbles
If you roll a 1 on a defence roll, the attack is a critical hit. This may cause additional effects, such as increased damage, status conditions, or extra consequences depending on the source of the attack.
If you roll a 20 on a defence roll, it is a critical fumble for the attacker. You avoid the attack completely, and may gain additional benefits such as causing the attacker to stumble, drop a weapon, or suffer some disadvantage — at the DM's discretion.

COVER
Walls, trees, creatures, and other obstacles can provide cover during combat, making a target more difficult to harm. A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.
There are three degrees of cover. If a target is behind multiple sources of cover, only the most protective degree of cover applies; the degrees aren't added together. For example, if a target is behind a creature that gives half cover and a tree trunk that gives three-quarters cover, the target has three-quarters cover.
A target with half cover has a +2 bonus to AC and Reflexes. A target has half cover if an obstacle blocks at least half of its body. The obstacle might be a low wall, a large piece of furniture, a narrow tree trunk, or a creature, whether that creature is an enemy or a friend.
A target with three-quarters cover has a +5 bonus to AC and Reflexes. A target has three-quarters cover if about three-quarters of it is covered by an obstacle. The obstacle might be a portcullis, an arrow slit, or a thick tree trunk.
A target with total cover can't be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.

DAMAGE AND HEALING
Injury and the risk of death are constant companions of those who explore the world. The thrust of a sword, a well-placed arrow, or a blast of flame from a fireball spell all have the potential to damage, or even kill, the hardiest of creatures.
Hit Points
Hit points represent a combination of physical and mental durability, the will to live, and luck. Creatures with more hit points are more difficult to kill. Those with fewer hit points are more fragile.
A creature's current hit points (usually just called hit points) can be any number from the creature's hit point maximum down to 0. This number changes frequently as a creature takes damage or receives healing.
Whenever a creature takes damage, that damage is subtracted from its hit points. The loss of hit points has no effect on a creature's capabilities until the creature drops to 0 hit points.
Describing the Effects of Damage
Dungeon Masters describe hit point loss in different ways. When your current hit point total is half or more of your hit point maximum, you typically show no signs of injury. When you drop below half your hit point maximum, you show signs of wear, such as cuts and bruises. An attack that reduces you to 0 hit points strikes you directly, leaving a bleeding injury or other trauma, or it simply knocks you unconscious.
Damage Rolls
Each weapon, spell, and harmful monster ability specifies the damage it deals. You roll the damage die or dice, add any modifiers, and apply the damage to your target. Magic weapons, special abilities, and other factors can grant a bonus to damage.
When attacking with a weapon, you use your Strength modifier to determine the bonus damage. A spell tells you which dice to roll for damage and whether to add any modifiers.
If a spell or other effect deals damage to more than one target at the same time, roll the damage once for all of them. For example, when a wizard casts fireball or a cleric casts flame strike, the spell's damage is rolled once for all creatures caught in the blast.
Critical Hits: When you make an attack roll and get a natural 20 (the d20 shows 20), you hit regardless of your target's Armor Class, and you have scored a threat. The hit might be a critical hit (or “crit”). To find out if it's a critical hit, you immediately make a critical roll—another attack roll with all the same modifiers as the attack roll you just made. If the critical roll also results in a hit against the target's AC, your original hit is a critical hit. (The critical roll just needs to hit to give you a crit. It doesn't need to come up 20 again.) If the critical roll is a miss, then your hit is just a regular hit.
A critical hit means that you roll your damage more than once, with all your usual bonuses, and add the rolls together. Unless otherwise specified, the threat range for a critical hit on an attack roll is 20, and the multiplier is x2.
Exception: Extra damage over and above a weapon's normal damage is not multiplied when you score a critical hit.
Increased Threat Range: Sometimes your threat range is greater than 20. That is, you can score a threat on a lower number. In such cases, a roll of lower than 20 is not an automatic hit. Any attack roll that doesn't result in a hit is not a threat.
Increased Critical Multiplier: Some weapons deal better than double damage on a critical hit.
Spells and Critical Hits: A spell that requires an attack roll can score a critical hit. A spell attack that requires no attack roll cannot score a critical hit.
Damage Types
Different attacks, damaging spells, and other harmful effects deal different types of damage. Damage types have no rules of their own, but other rules, such as damage resistance, rely on the types.
The damage types follow, with examples to help a DM assign a damage type to a new effect.
Acid. The corrosive spray of a black dragon's breath and the dissolving enzymes secreted by a black pudding deal acid damage.
Bludgeoning. Blunt force attacks — hammers, falling, constriction, and the like — deal bludgeoning damage.
Cold. The infernal chill radiating from an ice devil's spear and the frigid blast of a white dragon's breath deal cold damage.
Fire. Red dragons breathe fire, and many spells conjure flames to deal fire damage.
Force. Force is pure magical energy focused into a damaging form. Most effects that deal force damage are spells, including magic missile and spiritual weapon.
Lightning. A lightning bolt spell and a blue dragon's breath deal lightning damage.
Negative energy. Negative energy damage withers matter and even the soul.
Piercing. Puncturing and impaling attacks, including spears and monsters' bites, deal piercing damage.
Positive energy. Positive energy damage, sears the flesh like fire and overloads the spirit with power.
Slashing. Swords, axes, and monsters' claws deal slashing damage.
Sonic. A concussive burst of sound deals sonic damage.
Energy Resistance and Vulnerability
Some creatures and objects are exceedingly difficult or unusually easy to hurt with certain types of damage.
If a creature or an object has resistance to a damage type, damage of that type is reduced against it by the amount of resistance. If a creature or an object has vulnerability to a damage type, damage of that type is increased by 50% against it.
Resistance and then vulnerability are applied after all other modifiers to damage. For example, a creature has resistance 10 to fire damage and is hit by an attack that deals 25 fire damage. The creature is also within a magical aura that reduces all damage by 5. The 25 damage is first reduced by 5 and then reduced by 10, so the creature takes 10 damage.
If Multiple instances of resistance or vulnerability that affect the same damage type, only the higher is applied.
Damage Reduction
A creature with damage reduction (DR) ignores a set amount of damage from most physical attacks, except for specific vulnerabilities. It still takes full damage from energy attacks, spells, and supernatural abilities.
DR is bypassed by certain types of weapons (e.g., piercing, bludgeoning, or slashing) or materials (e.g., silver, adamantine, or cold iron). Magic weapons can overcome some creatures' DR. Some creatures are vulnerable to weapons with specific alignments (chaotic, evil, good, or lawful). If DR has a dash (–), no weapon bypasses it. Some creatures require weapons with multiple properties to overcome their DR. DR negates most special effects tied to an attack but does not block energy damage, touch attacks, or certain poisons and diseases. If a creature has multiple DR sources, only the best applies in a given situation.
Healing
Unless it results in death, damage isn't permanent. Even death is reversible through powerful magic. Rest can restore a creature's hit points and magical methods such as a cure wounds spell can remove damage in an instant.
When a creature receives healing of any kind, hit points regained are added to its current hit points. A creature's hit points can't exceed its hit point maximum, so any hit points regained in excess of this number are lost.
A creature that has died can't regain hit points until magic such as the revivify spell has restored it to life.
Dropping to 0 Hit Points
When you drop to 0 hit points, you either die outright or fall unconscious, as explained in the following sections.
Instant Death
Massive damage can kill you instantly. When damage reduces you to 0 hit points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum.
For example, a character with a maximum of 12 hit points currently has 6 hit points. If she takes 18 damage from an attack, she is reduced to 0 hit points, but 12 damage remains. Because the remaining damage equals her hit point maximum, she dies.
Falling Unconscious
If damage reduces you to 0 hit points and fails to kill you, you fall unconscious. This unconsciousness ends if you regain any hit points.
Death Saving Throws
Whenever you start your turn with 0 hit points, you must make a special saving throw, called a death saving throw, to determine whether you creep closer to death or hang onto life. Unlike other saving throws, this one isn't tied to any ability score. You are in the hands of fate now, aided only by spells and features that improve your chances of succeeding on a saving throw.
Roll a d20. If the roll is 10 or higher, you succeed. Otherwise, you fail. A success or failure has no effect by itself. On your third success, you become stable (see below). On your third failure, you die. The successes and failures don't need to be consecutive; keep track of both until you collect three of a kind. The number of both is reset to zero when you regain any hit points or become stable.
Rolling 1 or 20. When you make a death saving throw and roll a 1 on the d20, it counts as two failures. If you roll a 20 on the d20, you regain 1 hit point.
Damage at 0 Hit Points. If you take any damage while you have 0 hit points, you suffer a death saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death.
Stabilizing a Creature
The best way to save a creature with 0 hit points is to heal it. If healing is unavailable, the creature can at least be stabilized so that it isn't killed by a failed death saving throw.
You can use your action to administer first aid to an unconscious creature and attempt to stabilize it, which requires a successful DC 10 Wisdom (Medicine) check.
A stable creature doesn't make death saving throws, even though it has 0 hit points, but it does remain unconscious. The creature stops being stable, and must start making death saving throws again, if it takes any damage. A stable creature that isn't healed regains 1 hit point after 1d4 hours.
Monsters and Death
Most DMs have a monster die the instant it drops to 0 hit points. Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.
Knocking a Creature Out
Sometimes an attacker wants to incapacitate a foe, rather than deal a killing blow. When an attacker reduces a creature to 0 hit points with a melee attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls unconscious and is stable.
Temporary Hit Points
Some spells and special abilities confer temporary hit points to a creature. Temporary hit points aren't actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.
When you have temporary hit points and take damage, the temporary hit points are lost first, and any leftover damage carries over to your normal hit points. For example, if you have 5 temporary hit points and take 7 damage, you lose the temporary hit points and then take 2 damage.
Because temporary hit points are separate from your actual hit points, they can exceed your hit point maximum. A character can, therefore, be at full hit points and receive temporary hit points.
Healing can't restore temporary hit points, and they can't be added together. If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones. For example, if a spell grants you 12 temporary hit points when you already have 10, you can have 12 or 10, not 22.
If you have 0 hit points, receiving temporary hit points doesn't restore you to consciousness or stabilize you. They can still absorb damage directed at you while you're in that state, but only true healing can save you.
Unless a feature that grants you temporary hit points has a duration, they last until they're depleted or you finish a long rest.

MOUNTED COMBAT
A knight charging into battle on a warhorse, a wizard casting spells from the back of a griffon, or a cleric soaring through the sky on a pegasus all enjoy the benefits of speed and mobility that a mount can provide.
A willing creature that is at least one size larger than you and that has an appropriate anatomy can serve as a mount, using the following rules.
Mounting and Dismounting
Once during your move, you can mount a creature that is within 5 feet of you or dismount. Doing so costs an amount of movement equal to half your speed. For example, if your speed is 30 feet, you must spend 15 feet of movement to mount a horse. Therefore, you can't mount it if you don't have 15 feet of movement left or if your speed is 0.
If an effect moves your mount against its will while you're on it, you must succeed on a DC 10 Dexterity saving throw or fall off the mount, landing prone in a space within 5 feet of it. If you're knocked prone while mounted, you must make the same saving throw.
If your mount is knocked prone, you can use your reaction to dismount it as it falls and land on your feet. Otherwise, you are dismounted and fall prone in a space within 5 feet it.
Controlling a Mount
While you're mounted, you have two options. You can either control the mount or allow it to act independently. Intelligent creatures, such as dragons, act independently.
You can control a mount only if it has been trained to accept a rider. Domesticated horses, donkeys, and similar creatures are assumed to have such training. The initiative of a controlled mount changes to match yours when you mount it. It moves as you direct it, and it has only three action options: Dash, Disengage, and Dodge. A controlled mount can move and act even on the turn that you mount it.
An independent mount retains its place in the initiative order. Bearing a rider puts no restrictions on the actions the mount can take, and it moves and acts as it wishes. It might flee from combat, rush to attack and devour a badly injured foe, or otherwise act against your wishes.
In either case, if the mount provokes an opportunity attack while you're on it, the attacker can target you or the mount.

UNDERWATER COMBAT
When adventurers pursue sahuagin back to their undersea homes, fight off sharks in an ancient shipwreck, or find themselves in a flooded dungeon room, they must fight in a challenging environment. Underwater the following rules apply.
When making a melee weapon attack, a creature that doesn't have a swimming speed (either natural or granted by magic) has a -2 malus on the attack roll and deals half damage unless the weapon is deals piercing damage.
A ranged weapon attack automatically misses a target beyond the weapon's normal range. Even against a target within normal range, the attack roll has -2 malus on th attack roll unless the weapon is a crossbow, a net, or a weapon that is thrown like a javelin (including a spear, trident, or dart).
Creatures and objects that are fully immersed in water have resistance 20 to fire damage.