Dungeons & Dragons gameplay

Beginning with the 3rd Edition, each score has a corresponding ability modifier, where Modifier = Score − 10/2, rounded down.[5] It acts as a bonus or penalty depending on a character's ability scores. This modifier is added to the appropriate dice rolls.[5][6] For example, the strength modifier would be added to the damage dealt by a sword, the dexterity modifier to Armor Class (see below) as the character's ability to dodge attacks, and the charisma modifier to an attempt to smooth-talk a merchant.

In AD&D, ability scores were "determined by rolling three 6-sided die and adding up their values".[7] This had a significant impact on character creations as "certain classes could only be taken up by characters with the right combination of statistics. As a result, players often" re-rolled characters until they ended up with the combination of ability scores they desired.[3]^:149 "A point system to ensure total player control over the character's attributes while at the same time limiting just how powerful the character could become [...] [was] formalized in the third edition".[3]^:149

There are now several methods of determining a character's initial ability scores during character creation:

• Rolling dice (3d6): This is the standard method for older editions. For each ability score, the player rolls 3d6, and adds the values, resulting in scores ranging from three to eighteen, averaging between 10 and 11.[7]
• Rolling dice (4d6, keep 3): This is the standard method since 3rd edition.[8] For each ability score, the player rolls 4d6, and adds the three highest values, resulting in scores ranging from three to eighteen, skewed towards higher numbers, averaging 12.2446, though the most probable result is 13.[9]
• Predetermined array of scores: Each player uses the same set of numbers, choosing which ability score to apply them to.[6][10]
• Point buy: In the point buy system, a player has a certain number of points to spend on ability scores, and each score has a certain point cost affixed to it, where higher scores cost more points than lower ones.[6][10]

• Comeliness (COM): In the original version of AD&D, Comeliness was introduced as a seventh ability score in the supplemental rulebook Unearthed Arcana and Oriental Adventures to differentiate between physical attractiveness and charisma. Comeliness has not appeared as an officially supported ability score since, although the second edition rules Player's Option: Skills & Powers introduced "appearance" as one of twelve subability scores.
• Sanity (SAN): An optional score suggested in the 5th Edition Dungeon Master's Guide for campaigns shaped by the constant risk of insanity. It is checked for actions like understanding the writings of raving lunatics and used for dedicatedly dealing with resisting the equally optional madness damage type, caused for example by contact with alien planes of existence (or their denizens) that defy the rules of the material plane.
• Honor (HON): Also suggested in the 5th Edition Dungeon Master's Guide, an option for campaigns shaped by a strict code of honor like East Asia–inspired ones or those with a focus on chivalry of any sort. It determines both how well the character adheres to the respective society's code and how well he understands its tenets. It may also reflect others' perception of the character's honorability. Mechanically, high (or low) honor is used in social interaction in situations in which it may be more relevant than a person's charisma or in a saving throw to resist (for example) the urge to act dishonorably. Unlike others, this ability score can not be raised by the player after character creation. Instead, the dungeon master can increase (or decrease) its value by 1 at the end of an adventure according to the player character's actions throughout it.

Armor class (AC) is a rating used to determine how difficult it is to damage a creature/character. It is based on several factors such as a creature's natural aversion to physical injury, magical enhancements, and any protective garments worn.[3][4] The dexterity ability score grants bonuses to AC.

• In the original game, armor class ranged from 9 to 0, because armor and dexterity modifiers were applied to hit rolls instead. Negative values first appeared in the Greyhawk supplement, because it first applied them directly to the Armor Class.[11]
• In editions prior to 3rd, armor class ranges from -10 to 10. Having an AC of 10 was the weakest, and a -10 being the strongest possible written AC.[12]
• In subsequent editions, armor class instead starts at 10 and increases. Extremely non-dexterous or non-moving creatures may suffer penalties that lower their armor class below 10.

In 4th edition, there are three defenses that function similarly to armor class. Fortitude is based on strength or constitution; it represents a character's endurance to pain. Reflex is based on dexterity or intelligence and can be modified by a shield; it represents a character's ability to dodge. Will is based on wisdom or charisma; it represents a character's strength of mind and resistance to mental attack. These defenses are typically lower than AC, so an attack against fortitude is usually better than an attack against AC.[6]

Hit points (HP) are a measure of a character's vitality or health; they are determined by the character's class or race, and Constitution score. Hit points are reduced whenever a character takes damage.[2][3]

In the original D&D game a character died when his/her hit point total reached 0. First edition AD&D introduced an optional rule in which a character died when his/her hit points reached -10, with beings falling unconscious at 0 HP, and creatures reduced to negative HPs continue to lose HPs due to bleeding, etc. unless they are stabilized by aid or healing (natural or magical). In third edition, this rule became part of the core rules.

In 4th Edition, death occurs when a character's hit point value is reduced to half their total expressed as a negative number.[6] For example, if a character has hit points of 52, the character is unconscious and dying at 0 hit points and death occurs when the character's hit points reach -26.

In 5th Edition, a character is killed automatically if the damage is greater than the negative value of their maximum hit points. Otherwise, a player at 0 hit points must begin making "death saving throws", where an unmodified d20 roll resulting in 10 or above is a success, below 10 a failure. If the player gets three failures before three successes, the character is dead. If three successes are recorded, the character is stable but unconscious. A result of 1 counts as two failures, while a result of 20 is automatic success and the character regains 1 hit point. A fellow player may attempt to stabilize their companion using a medicine skill check, or use more advanced healing options.[10]

Certain situations give characters the chance to avoid special types of danger or attacks. These chances are called saving throws or saves. A saving throw is made when a character would come to harm from extraordinary means such as poisons and magical compulsions in nature.[4]

In the early editions of D&D, there are five categories of saving throws, based on the form of the potential damage:

• Paralysis, Poison, or Death Magic
• Petrification or Polymorph
• Rods, Staves, Wands – against magical devices
• Spells
• Breath Weapons – such as with dragons or gorgons

In 3rd Edition, they were reduced to three kinds of saving throw based on what aspect of the character was under threat.

• Fortitude – A Fortitude save represents physical toughness. Fortitude saves involve a character's resistance to an effect that directly attacks his health, stamina, or soul. Fortitude saves are affected by the constitution ability score.[4]
• Reflex – A Reflex save represents physical agility. Reflex saves are affected by the dexterity ability score.[4]
• Will – A Will saves involve a character's mental resistance to mental dominance, confusion, stress, and insanity. Will saves are affected by the wisdom ability score.[4]

In 4th Edition there is only one type of saving throw.[6] Saving throws are usually rolled after a character has already been affected by an attack (by hitting the character's AC or fortitude, reflex, or will defense, defenses which the 3rd Edition saves had been converted into), rolled each round to give the character a chance to shake off the effect. They are meant partly to simplify record-keeping for effects that last more than one round but less than the encounter.

In 5th Edition, saving throws are explicitly tied to the ability scores, and carry their names, resulting in six categories of saves. A saving throw is performed similarly to a skill check, with a d20 roll result added to the relevant ability modifier and, if applicable, the proficiency bonus.[10]

When a character makes an attack, a 20-sided die is rolled to determine success/failure. The result could be adjusted based on any number of possible modifiers the character or its intended target have.[4]

The number added to the die roll is actually several different modifiers combined, coming from different places. These modifiers include the character's proficiency with the specific weapon and weapons in general, the quality of the weapon (masterwork craftsmanship or magical enhancements), the modifier of the ability associated with the weapon (strength for melee weapons, and dexterity for ranged weapons), magical effects improving/hampering the character's ability to attack, and any special experience the character has fighting a certain foe.[4]

• In the early editions, the final result is compared to a table along with the target's armor class to see if the attack hits. Every general class type had its own matrix-style table, while monsters used the same matrix as the generic fighter character type.
• In AD&D 2nd Edition, if the final result equals or exceeds the attacker's THAC0 (the pre-recorded number the character needs To Hit Armor Class 0"), the attacker has successfully hit a target with armor class 0. If the target has an armor class different from zero (which is far more likely than not), the target's armor class is subtracted from the attacker's THAC0, and that number is what the attacker's roll must equal or exceed to see if the attack hits. This method was informally introduced before the publication of 2nd Edition as a shortcut for players to use.
• Since 3rd Edition, the attack hits simply if the final result is equal to or greater than the target's armor class.[13]

The combat mechanic is turn-based and operates in rounds.[4] A round is a discrete time interval (approximately 6 seconds, game-time in later editions, and approximately 1 minute in earlier editions) in which all involved parties act in the combat. The order in which parties involved in the combat act is determined by Initiative.

• In older editions, characters are allowed to move their speed and attack every round, or perform a reasonable combination of other actions.
• In 3rd and 3.5 editions, what a character can and cannot do in a given round is more codified; a character may perform one standard and one move action, two move actions or one full-round action in a round, along with any number of free actions, and a single swift or immediate action. Unlike other types of actions, immediate actions may also be taken during someone else's turn, though that counts as using the immediate action slot for the character's following turn.
• In 4th edition, a character is allotted one standard action, one move action, one minor action, and any number of free actions to be performed during his or her turn. Each action can be downgraded, such as replacing a standard action with a move action or a move action with a minor action. In addition, a character may take one opportunity action during each other character's turn, and one immediate action during any round, defined as the time between the end of the character's turn and the beginning of his next turn. Immediate and opportunity actions each have a defined trigger that allows their use, based on other characters' actions, and are categorized as reactions that are resolved after the trigger or as interrupts that are resolved before or in place of the triggering event. Neither immediate nor opportunity actions may be taken during the character's turn.[6]
• In 5th edition, a character may move up to their full allowed distance and take an action each turn, in any combination the player chooses. Some class features, spells and other circumstances allow a bonus action as well. Reactions triggered by outside factors, such as opportunity attacks, may occur on a player's turn or someone else's.[10]