Dungeons & Dragons game mechanics

In the 3rd edition Dungeons & Dragons role-playing game, game mechanics and die rolls determine much of what happens.

Ability scores
All characters have six basic statistics:
 * Strength (STR): Strength is a measure of muscle, endurance and stamina combined. Strength affects the ability of characters to lift and carry weights and make effective melee attacks.
 * Dexterity (DEX): Dexterity encompasses a number of physical attributes including hand-eye coordination, agility, reflexes, fine motor skills, balance and speed of movement; a high dexterity score indicates superiority in all these attributes. Dexterity affects characters with regard to initiative in attack, the projection of missiles from hand or other means, and in defensive measures. Dexterity is the ability most influenced by outside influences (such as armor).
 * Constitution (CON) Constitution is a term which encompasses the character's physique, toughness, health and resistance to disease and poison. The higher a character's Constitution, the more hit points that character will have. Unlike the other ability scores, which knock the character unconscious when they hit 0, having 0 Constitution is fatal.
 * Intelligence (INT) Intelligence is similar to IQ, but also includes mnemonic ability, reasoning and learning ability outside those measured by the written word. Intelligence dictates the number of languages a character can learn and the number of spells a Wizard may know.
 * Wisdom (WIS) Wisdom is a composite term for the characters enlightenment, judgement, wile, willpower and intuitiveness.
 * Charisma (CHA) Charisma is the measure of the character's combined physical attractiveness, persuasiveness, and personal magnetism. A generally non-beautiful character can have a very high charisma due to strong measures of the other two aspects of charisma.

An ability score is a natural number, with a value of 10 or 11 representing average ability.

3.0 and 3.5 editions
Each score has a modifier (mod) associated with it that is equal to half of X−10 (where X is the ability's score), rounding down. So, for example, an ability score of eight, two lower than ten, would mean a modifier of −1, while an ability score of 17, 7 above ten, means a modifier of +3 (7 = 3 × 2 + 1). This modifier is added to the appropriate dice rolls. For example, the strength mod would be added to the damage dealt by a sword, the dexterity mod to Armor Class (see below) as the character's ability to dodge attacks, and the charisma mod to an attempt to smooth-talk a merchant.

There are creatures that lack certain ability scores (undead, for example, have no constitution). These are called nonabilities and affect how that creature is treated by certain spells and effects. The aforementioned undead, for example, are immune to almost anything that requires a Fortitude save, unless it can also affect objects. This is not the same as having a score of zero.

Determining ability scores
There are several methods of determining a character’s initial ability scores during character creation:


 * Rolling dice (3d6): This is the standard method for some pre-3.0 editions. For each ability score, the player rolls 3d6, and adds the values, resulting in scores ranging from three to eighteen, averaging around 10.
 * Rolling dice (4d6k3): This is the standard method for 3.0 and 3.5 editions. 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


 * Predetermined array of scores: Less random, but inflexible.
 * Point buy: In the point buy system, a player has a certain number of points to spend on their ability scores. The more powerful the characters are intended to be, the more points will be available to the players. (Characters are usually more powerful for a more difficult game.) Possible ability scores range from eight to eighteen, and each score has a certain point cost affixed to it, where higher scores tend to cost more points per level than lower ones. This method is used in Dungeons & Dragons Online to avoid imbalanced characters getting an unfair advantage over other players.

Special qualities

 * Darkvision: This refers to the ability of a creature to see in the dark. It allows the creature to discern shapes (as in normal, daylight vision) but only in shades of grey. Darkvision was introduced in the 3.0 edition of the game to replace infravision, which had become seen by some designers of the game as too logically inconsistent to continue using as-is.
 * Infravision: The predecessor of darkvision, in pre-3.0 editions of the game, this allowed some races to see in darkness by discerning the heat signatures left behind by other creatures.

Combat
The combat mechanic is turn-based and operates in rounds. A round is a discrete time interval in which all involved parties act in the combat. The order in which parties involved in the combat act is determined by Initiative.

Armor Class
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.
 * In editions of the game prior to 3.0, Armor Class starts at 10 and decreases, and so having a lower armor class is better.
 * In 3.0 and 3.5 editions, armor class instead starts at 10 and increases.

Hit points
Hit points (HP) are a measure of a characters vitality or health; they are determined by the character's class (certain occupations breed hardier people) or race, and Constitution score. Hit points are reduced whenever a character takes damage.

Saving Throws
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.

Pre-d20 System
In pre-d20 System editions of D&D, there are five categories of saving throws:
 * '''Poison, Death Magic
 * Paralyzation, Petrification, or Polymorph
 * Rod, Staff, Wand
 * Spells
 * Breath Weapon

3rd Edition
There are three kinds of Saving Throws:
 * Fortitude: A Fortitude save involves a character's resistance to an effect that directly attacks his health, stamina, or soul. This includes resisting poison, shrugging off the worst of a flesh to stone spell, and ignoring the horrible stench that surrounds a ghast.
 * Reflex: A Reflex save involves a character's ability to move out of the way of an incoming object or spell effect as well as his ability to leave an area in a short amount of time. This includes the character's ability to dodge falling rocks and his ability to escape the worst of a Fireball spell.
 * Will: A Will save involves a character's mental resistance to mental dominance, confusion, stress, and insanity. This includes the character's ability to resist a charm person spell, see through an illusion, and to resist supernatural fear.

Attacking
When a character makes an attack, a 20-sided die is rolled and a certain number is added to determine success/failure.

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 (superior craftsmanship or magical enhancements), the modifier of the ability associated with the weapon (strength for melee, or close-quarters, 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.

In 3.0 and 3.5 editions
If the dice roll, plus all applicable modifiers, is higher than the defender's armor class (see above), then the attacker hits the defender and can proceed to the next step, determining damage.

If the attacker hits the defender, he proceeds to determine damage. A certain die is rolled, depending on the weapon being used; the more powerful the weapon, the more damage it is capable of doing, and the higher (number of sides and/or number of dice) its damage die will be, for a higher possible damage roll. To this damage roll, modifiers are added, including strength bonus (melee weapons only), weapon quality, and magic affecting the attacker. The damage roll, plus all applicable modifiers, is deducted from the defender's hit points (see below).

Should a character roll a natural 20 on a die roll, the hit is a critical threat. He rolls again, and, if this next roll shows a hit, he has scored a critical hit (crit for short) and deals extra damage, depending on the weapon (anywhere from twice the damage to four times the damage). If the player misses after a threat (roll a natural 1 or total attack roll is less than target's Armor Class), it will count as a normal hit without multipliers. For some weapons, the player need not roll a natural 20 to score a threat; a 19 to 20 or a 17 to 20 will do. If the player misses after any threat less than a natural 20, the whole attempt is a miss. A roll of a natural 1 is always a miss, while a natural 20 is always a hit regardless of bonuses or penalties.

Threatened Area and Attacks of Opportunity
When a character is considered armed, he has physical influence and an amount of control over the nearby area. This area is called the threatened area. The threatened area is determined by the character's reach with the weapon he is using. Most weapons use the creature's natural reach based on his size, but some weapons, such as polearms, are long enough that they extend the character's reach and allow the character to threaten more area. Characters who gain more reach by being larger than normal threaten all area from the spot they are standing on to the fullest extent of their reach. Characters who gain a reach advantage by using a weapon with longer reach, however, usually threaten the area at the fullest extent of their reach and slightly before it, and do not threaten the area immediately in front of them (this happens with most polearms, such as longspears, glaives, and halberds; a spiked chain is special in that it has the reach of a polearm but still threatens the immediate area).

A character can only make a melee attack on a target that is inside of his threatened area. This means that, for example, a medium-sized creature who is using a longsword of appropriate size threatens only the squares adjacent to him and is therefore limited to targets adjacent to him when making a melee attack, but a medium-sized character who is using a longspear of appropriate size threatens the second square away from him in all directions and cannot make a melee attack on a creature in an adjacent square.

If an opponent performs an action that lets his guard down within a character's threatened area, this is said to provoke an Attack of Opportunity. There is a listing in the Players Handbook of the actions that provoke an Attack of Opportunity, and special combat actions often mention in the explanation of their mechanics whether or not the action provokes an Attack of Opportunity. Examples of actions that provoke an Attack of Opportunity are standing up from a prone position, initiating a grapple, casting a spell, and using a move action to move through threatened area.

A character using a ranged weapon does not threaten the area within range of his ranged weapon.

An Attack of Opportunity is a free attack that is taken immediately, and likely out of turn (in the middle of another character's action). Regardless of how many attacks a character has performed in a round, he may always take at least one Attack of Opportunity in a combat round. A character is limited to a single Attack of Opportunity in any given combat round unless special circumstances apply, such as possession of the Combat Reflexes feat, which allows a character to take a number of additional Attacks of Opportunity in a round equal to his Dexterity modifier, if positive.

"Attack of Opportunity" is commonly shortened to "Attack of Op."

(The Opportunist class ability of the Rogue character class allows the Rogue to take an Attack of Opportunity against a creature in his threatened area who has just taken damage from a successful attack.)

In 3.0 and 3.5 editions
Actions are ordered by descending Initiative. On a participant's turn, given no special circumstances (which happen more frequently in higher-level combat), the most he can do is to perform an action that is as long as a full-round action. Any participant can always opt to do nothing at all. By standard rules, Initiative is rolled only once at the very beginning of the combat, and that Initiative order determines the order that all participants will act in every round of combat until the combat is over. Previous editions of Dungeons & Dragons had Initiative rerolled every round. A common house rule is to roll Initiative again every round to redetermine the order of actions in any given round. The combat is considered to end when there are no more combat actions to be taken (e.g. when the opposing side is defeated or has fled, or if some event halts the combat).

Physical dimensions in a combat are almost always divided into distances of 5 feet; most game mechanics that involve distance operate in divisions of five feet, such as a the space a creature takes up and how far he can reach.

Full-Round Actions
Unless special circumstances apply, a participant in combat has a full-round action to work with. Many actions are considered to take up the entirety of a participant's turn, such as taking multiple attacks on an opponent as his Base Attack Bonus allows, performing a coup de grace, running as fast as he can, or, if the character is a Sorcerer, to cast a spell that is enhanced by a Metamagic Feat.

The full-round action can also be divided into one move/move-equivalent action and one standard action.

The standard action can be considered the focus of the round's action, and the move/move-equivalent action is most commonly the setup to make the standard action possible or more effective. For this reason, the standard action can be thought of as meaningfully longer than the move/move-equivalent action (which is why a round cannot be split up into two standard actions, but a character can take full-round actions that are equivalent to two individual move/move-equivalent actions, such as drawing a weapon and moving in one round, or reloading a light crossbow and quaffing a potion).

Standard Actions
A standard action is usually the most effortful action taken in a round if the full-round action is divided. It is common, especially in lower-level combat, for a participant in combat to take only a standard action and intentionally forego all other actions he is entitled to for the round, whereas a move/move-equivalent action is most commonly followed by a standard action.

Examples of a standard action are making a single attack, casting a spell with a casting time of "1 action," and imbibing a magical potion. Because a character can always opt to do less than he is potentially able, he may replace his standard action with a move action, allowing him to take two move/move-equivalent actions as his activity for the round.

Move/Move-Equivalent Actions
During a move action, a participant in the combat can move a distance up to twice his base movement speed, with respect to special circumstances. When moving through another participant's threatened area, however, a moving character can provoke an Attack of Opportunity. There are special forms of movement that can be carried out on a move action as well, such as use of the Climb, Jump, Swim, and Tumble skills.

Also, if a character has the Spring Attack feat, he may make a move action, followed by a standard attack (a standard action used to make a single attack), and then take yet another move action after the standard attack, provided that the total distance he moves is not more than he could move in a single move action.

Instead of taking a move action, a character can choose instead to take a move-equivalent action. As the name implies, a move-equivalent action is considered to take up the same amount of time as a move action, provided that the character is not taking a move action while doing so. Examples of move-equivalent actions include standing up from a prone position, drawing a weapon, and reloading a light crossbow.

(A character with the Spring Attack feat cannot replace one of his move actions with a move-equivalent action.)

Free Actions
A free action is an action that takes so little time and effort to perform that it doesn't count against the character's allotted actions for the round. Examples of a free action include shouting battle orders, casting a spell enhanced with the Quicken Spell metamagic feat, and taking a five-foot step.

The five-foot step is one of the most popular free actions taken in a round. A character can take a five-foot step provided that he does not perform a move action in the same round. A five-foot step does not provoke an Attack of Opportunity like a move action can, which makes it an excellent action to take when surrounded by opponents.

A character can take any number of free actions in a round, provided that he does not perform the same free action twice, e.g. a character cannot take more than one five-foot step in a single round. (This rule, like most rules of the game, can be broken by special circumstances. For example, a character with the Multispell feat (an epic feat) can cast more than one Quickened Spell per round, which amounts to taking the same free action more than once in a round.)

Skills
Dungeons and Dragons, starting with the third edition of the game and continuing to present, has many skills that characters may train in. Characters gain skill points for buying skill ranks based on class, level, and intelligence. Some skills can only be taken by certain classes, such as Read Lips or Animal Empathy. These skills are called exclusive skills. Others can be used even if the character has no ranks in that skill (i.e., is not trained in that skill).

A skill check is always a d20 roll, with bonuses from the number of skill ranks, the skill's key ability, and any miscellaneous modifiers (from spells or racial abilities, for instance). Sometimes, a skill check may be aided by favorable circumstances (such as you brandishing a weapon while using Intimidate) or hampered by unfavorable circumstances (such as using improvised tools to pick a lock).

An example of a skill is Search, which is Intelligence-based; an example of a miscellaneous modifier which could be applied to search is the +5 competence bonus for a character wearing the "Goggles of Minute Seeing". Other skills include Diplomacy (CHA), Escape Artist (DEX), Swim (STR), various Knowledge skills (like Knowledge (Arcana) or Knowledge (Local)) (INT), Spot (WIS), and Concentration (CON).

A "check" is successful when the roll is higher than or equal to the difficultly class (DC) of the task. Usually, the Dungeon Master sets the DC. Sometimes the DC is set by the result of something else's check, this is an "opposed check". An example of an opposed check is spot against hide: the character is trying to see something else that is hidden.

Feats
Feats were introduced in the third edition of Dungeons and Dragons.

A feat is an ability that is learned and then used whenever it is befitting. You don't buy feats; you learn them as you progress in levels. If you don't have a feat or don't meet the prerequisites for a feat, you can't use it.

Feats are divided into several types, such as Metamagic and General. These types tell you which classes would be best suited for using a specific feat, for example, Metamagic feats work best when used by spellcasters, such as wizards.