The Order of Combat

A typical combat encounter is a clash between two sides, a flurry of weapon swings, feints, parries, footwork, and spellcasting. The game organizes the chaos of combat into a cycle of rounds and turns. A round represents about 6 seconds in the game world. During a round, each participant in a battle takes a turn. The order of turns is determined at the beginning of a combat encounter, when everyone rolls initiative. Once everyone has taken a turn, the fight continues to the next round if neither side has defeated the other. 

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 Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (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 round ends. A member of a group can be surprised even if the other members aren’t. 

Initiative

Initiative determines the order of turns during combat. When anybody decides they want to take an action that would start combat, every participant first makes a Dexterity check to determine their place in the initiative order. The DM makes one roll for an entire group of identical creatures, so each member of the group acts at the same time.

The DM ranks the combatants in order from the one with the highest Dexterity check total to the one with the lowest. This is the order (called the initiative order) in which they act during each round. The initiative order remains the same from round to round. 

If a tie occurs, the DM decides the order among tied DM-controlled creatures, and the players decide the order among their tied characters. The DM can decide the order if the tie is between a monster and a player character. Optionally, the DM can have the tied characters and monsters each roll a d20 to determine the order, highest roll going first, or it can be decided that the character with the higher Dexterity score 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.

Bonus Action

Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action. The Cunning Action feature, for example, allows a rogue to take a bonus action. You can take a bonus action only when a special ability, spell, or other feature of the game states that you can do something as a bonus action. You otherwise don’t have a bonus action to take. 

You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available. 

You choose when to take a bonus action during your turn, unless the bonus action’s timing is specified, and anything that deprives you of your ability to take actions also prevents you from taking a bonus action. 

Free Actions

Free actions are things you can do on your turn that don't cost anything.

Communicate. You can communicate however you are able, with brief utterances or gestures, during your turn.

Interact. You can interact with one object or feature of the environment for free, either during your move or as part of your action. For example, you can open a door as you move towards an enemy, or you can draw your sword as part of the same action you used to attack. If you want to interact with a second object on the same turn, you need to spend an action. The DM also may specify that you need to use an action when interacting with an object if it needs special care or when it presents an unusual obstacle. For example, the DM would require an action for you to open a jammed door, or to turn a crank to lower a drawbridge.

Reaction

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else’s.

 When you take a reaction, you can’t take another one until the start of your next turn. If the reaction interrupts another creature’s turn, that creature can continue its turn right after the reaction. 

Movement and Position

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. The rules for jumping, climbing, and swimming can be found in Chapter 8.

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 to the air to fly 30 more feet.

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, a condition described in chapter 11. 

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.

You can stand an ally up that was knocked prone using your movement on your turn. You must spend a number of feet equal to half the allies speed to stand them up. Alternatively, you can use the Help action to stand them up without using any of of your speed.

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. 

While you are prone, you have disadvantage on melee attacks and ranged attacks without the firearm or loading property. Additionally, melee attacks have advantage against you, and ranged attacks have disadvantage against you.

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, you provoke an opportunity attack, as explained later in the chapter. 

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 depending on their size. The size categories table below shows how much space a creature of a particular size controls in battle.

Tiny. 2.5 by 2.5 feet

Small. 5 by 5 feet

Medium. 5 by 5 feet

Large. 10 by 10 feet

Huge. 15 by 15 feet

Gargantuan. 20 by 20 feet, or larger

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.

Actions in Combat

When you take your action on your turn, you can take one of the actions presented here, an action you gained from your class or a special feature, or an action that you improvise. Many monsters have action options of their own in their stat blocks. 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. 

Certain features, such as the Extra Attack feature of the fighter, allow you to make more than one attack with this action. 

Cast a Spell

Spellcasters such as wizards and clerics, as well as many monsters, 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, a reaction, 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. See chapter 10 for the rules on spellcasting. 

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

You can replace an attack on your turn with disengage, or you can replace all your movement this turn with disengage. When you disengage, you do not provoke attacks of opportunity for the rest of your turn.

Dodge 

When you take the Dodge action, you focus entirely on avoiding attacks. Until the start of your next turn, any attack roll made against you has disadvantage if you can see the attacker, and you make Dexterity saving throws with advantage. 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 advantage on the next ability 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 advantage.

Hide

When you take the Hide action, you make a Dexterity (Stealth) check in an attempt to hide. Until you are discovered or you stop hiding, that check’s total is contested by the Wisdom (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, no matter what direction you approach from, even if you only pop out to make an attack. 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.

You can also be discovered by someone when they aren't searching. If their passive perception is higher than your stealth check, then they can see you.

If you succeed on your stealth check, you gain certain benefits, as described in the “Unseen Attackers and Targets” section later in this chapter. 

Ready

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 your reaction right after the trigger finishes or ignore the trigger. Remember that you can take only one reaction per round.

 When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell’s magic requires concentration (explained in chapter 10). If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missile with your reaction, your concentration might be broken. 

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 Wisdom (Perception) check or an Intelligence (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 advantage or disadvantage 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 an attack roll, you're making an attack.

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 disadvantage 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 advantage 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 disadvantage 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, you have disadvantage on the attack roll if you are within 5 feet of a hostile creature who can see you and who isn’t incapacitated.

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.

When you are unarmed, you can fight in melee by making an unarmed strike, which deals 1 damage + your strength modifier (minimum 1 damage).

Opportunity Attacks 

In a fight, everyone is constantly watching for enemies to drop their guard. You can rarely move heedlessly past your foes without putting yourself in danger; doing so provokes an opportunity attack. 

You can make an opportunity attack when a hostile creature that you can see moves out of your reach. You can make one melee weapon attack against that creature. The attack interrupts the provoking creature’s movement, occurring right before the creature leaves your reach. 

You can also make an opportunity attack when a hostile creature that you can see within your range makes an attack against another creature. You can make one melee weapon attack against the creature.

To make an opportunity attack, you must spend your reaction to do so.

Opportunity attacks do not trigger other opportunity attacks. For example, if your ally moves out of reach of a goblin that is within your reach, and the goblin makes an attack of opportunity on your ally, the goblin does not provoke an attack of opportunity from you because his attack that he just made was an opportunity attack.

You can avoid provoking an opportunity attack by Disengaging, as explained earlier in the chapter. You also don’t provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction. For example, you don’t provoke an opportunity attack if an explosion hurls you out of a foe’s reach or if gravity causes you to fall past an enemy. 

Two-Weapon Fighting 

When you take the Attack action and attack with a light melee weapon that you’re holding in one hand, you can use a bonus action to attack with a different light melee weapon that you’re holding in the other hand. You don’t add your ability modifier to the damage of the bonus attack, unless that modifier is negative. If either weapon has the thrown property, you can throw the weapon, instead of making a melee attack with it.

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 of a size that you can grapple, based on your Strength score (shown in the chart below), and it must be within your reach. Using at least one free hand, you try to seize the target by making a grapple check, a Strength (Athletics) check contested by the target’s Strength (Athletics) or Dexterity (Acrobatics) check (the target chooses the ability to use). If you succeed, you subject the target to the grappled condition. The condition specifies the things that end it, and you can release the target whenever you like (no action required). 

If the target is willing to be grappled, then you do not need to roll and the grapple succeeds automatically, even if the creature is of a size that you cannot grapple, however your speed is still affected by the size of the creature.

Escaping a Grapple. A grappled creature can use its action to escape. To do so, it must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check contested by your Strength (Athletics) check.

You can also aid another creature that is grappled. You can use an action to make a Strength (Athletics) check to pry the grappled creature out of the grapplers clenches, contested by the grapplers Strength (Athletics) check. You can alternatively use the Help action to give the grappled creature advantage on their next action they use to try to escape.

Moving a Grappled Creature. When you move while grappling another creature, you can drag or carry the grappled creature with you, but depending on the size of the creature and your strength score, your speed may be reduced. Use the Strength Chart below to determine.

If you have multiple targets grappled at once, you combine their sizes to determine the penalty to your speed. Two tiny creatures equals a small creature, two small creatures equal a medium creature, two medium creatures equal a large creature, two large creatures equal a huge creature, and two huge creatures equal a gargantuan creature. 

For example, if you were grappling two medium creatures, you would calculate your speed penalty as if you were grappling one large creature, and if you were grappling two large creatures, you would calculate your speed penalty as if you were grappling a huge creature. If you were grappling a medium creature and a small creature, you would still treat it as if you were grappling one medium creature, and if you were grappling a large creature and a medium creature, you would still treat it as if you were grappling one large creature.

Some speeds, such as flying speeds from certain effects or abilities, may be ineligible to use for carrying/dragging another creature at the DM's discretion.

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 a size that you are allowed to shove as shown in the Strength Chart above, and it must be within your reach. You make a Strength (Athletics) check contested by the target’s Strength (Athletics) or Dexterity (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. 

Disarming a Creature

A creature can use a weapon attack to knock a weapon or another item from a target’s grasp. The attacker makes an attack roll contested by the target’s Strength (Athletics) check or Dexterity (Acrobatics) check. If the attacker wins the contest, the attack causes no damage or other ill effect, but the defender drops the item. The attacker has disadvantage on its attack roll if the target is holding the item with two or more hands.

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 threequarters cover, the target has three-quarters cover. 

A target with half cover has a +2 bonus to AC and Dexterity saving throws. 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 Dexterity saving throws. A target has threequarters 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

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 add your ability modifier—the same modifier used for the attack roll— to the 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 score a critical hit, you roll the damage dice of the attack twice, and then add any relevant modifiers like normal. If the attack involves other damage dice, such as from the rogue’s Sneak Attack feature or paladin smite, you double those as well.

Damage 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 halved against it. If a creature or an object has vulnerability to a damage type, damage of that type is doubled against it.

Resistance and then vulnerability are applied after all other modifiers to damage. For example, if a creature has resistance to bludgeoning damage and is hit by an attack that deals 25 bludgeoning damage, and the creature is also within a magical aura that reduces all damage by 5, then the 25 damage is first reduced by 5 and then halved, so the creature would take 10 damage. 

Multiple instances of resistance or vulnerability that affect the same damage type count as only one instance. For example, if a creature has resistance to fire damage as well as resistance to all nonmagical damage, the damage of a nonmagical fire is reduced by half against the creature, not reduced by three-quarters. This does not apply with features like Evasion or Uncanny Dodge that specify a creature only suffers half damage, if a Rogue uses Uncanny Dodge to halve the damage of a an attack that they also have resistance to, they reduce the damage by three-quarters.

When damage is reduced to an amount that is not a whole number, the damage is rounded down unless otherwise stated by an ability or feature.

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 cleric 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, the cleric dies. 

Critical State

If damage reduces you to 0 hit points and fails to kill you, you enter the critical state. In the critical state, your walking speed is halved. At the start of each of your turns, you roll a death save, and then you may use either your action, bonus action, or move. If you use an action, you gain two levels of exhaustion. if you use a bonus action, you gain one level of exhaustion. If you use your reaction, you gain one level of exhaustion. You cannot benefit from any natural or magical climbing, swimming, or flying speeds you may have. You also cannot benefit from temporary hit points, and attack rolls against you have advantage.

You remain in the critical state until you regain at least 1 hit point. If you regain 1 hit point during your turn while in the critical state, you exit the critical state at the end of your turn, unless the hit point was regained from rolling a natural 20 on a death saving throw, in which case you exit the critical state at the start of your turn.

Death Saving Throws 

Whenever you start your turn with 0 hit points, you 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 successes and failures are reset when a creature is stabilized or when it regains at least one hit point.

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 from a single source 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 a creature in the critical state 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 in the critical state. If the creature takes any damage, they stop being stable and must start making death saving throws again. 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, rather than having it go into the critical state and make death saving throws. 

Mighty villains and special nonplayer characters are common exceptions; the DM might have them 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 or when the DM says the creature dies. 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

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. 

The creature must be at least one size category larger than you, it must be willing, and it must have the proper anatomy to serve as a mount. A creature without the proper anatomy, such as a humanoid, cannot serve as a mount.

If an effect moves your mount against its will while you’re on it, you must succeed on a DC 10 Strength or Dexterity (Animal Handling) check, 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 check. 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, and you may take your turns at the same time. 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. When you control the mount, the mount uses their own action and movement.

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 making a melee weapon attack while fully submerged under water, a creature that doesn’t have a swimming speed (either natural or granted by magic) has disadvantage on the attack roll unless the weapon is a dagger, javelin, shortsword, spear, or trident. 

A ranged weapon attack made while underwater automatically misses a target beyond the weapon’s normal range. Even against a target within normal range, the attack roll has disadvantage unless the weapon is a crossbow, a net, or a weapon that is thrown like a javelin (including a spear, trident, or dart). A firearm ranged weapon automatically misfires if it is shot underwater, regardless of its normal misfire score.

Creatures and objects that are fully immersed in water have resistance to fire damage.