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.

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 pre-3.0 editions of the game, the final result is compared to a table along with the target's Armor class to see if the attack hits.
 * In 3.0 and 3.5 editions, the attack hits if this final result is equal to or greater than the target's Armor Class.

Actions
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.


 * In pre-3.0 editions of the game, characters are allow to move their speed and attack every round, or perform a reasonable combination of other actions.
 * In 3.0 and 3.5 editions, what a character can and cannot do in a given round is more codified; a character may perform one full-round action, one standard and one move action, or two move actions 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.

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.