Dungeons & Dragons game mechanics

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


 * ability scores, the most basic statistics of a character
 * special qualities, what innately superhuman characteristics a character has
 * armor class, how well-protected a character is against physical attack
 * hit points, how much punishment a character can take before going unconscious or dying
 * saving throws, a character's defenses against nonphysical or area attacks
 * attack rolls and attacks, how effectively a character can damage another character
 * skills, how competent a character is in in various areas of expertise
 * feats, what special advantages a character has through natural aptitude or training

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.

Additional:
 * Comeliness In the original version of AD&D Comeliness was introduced as a 7th Ability Score/Stat in the supplemental rulebook "Unearthed Arcana" to differentiate between physical attractiveness and Charisma. Though the reasons behind its introduction were valid, due to the oft-abused practice of players automatically throwing their lowest score into what was considered to be an arguable 'useless' stat, Comeliness disappeared with the 2nd Edition to never reappear since.
 * Psionics Psionic Ability, Potential, or Strength Points (also known as PSPs) were arguably another Ability Score that was only enjoyed by those extraordinarily rare and lucky characters that successfully rolled for them, given their other stats. Many extraplanar beings (like Gods, Devils, and Archons) were psionically endowed by default in earlier editions of the game - however not all gaming campaigns and Dungeon Masters allow the use of Psionics due to its potentially disbalancing nature.

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 (3=(17-10)/2, rounded down). 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 both Ultravision and Infravision, which had become seen by some designers of the game as too logically inconsistent to continue using as-is.
 * Ultravision: The predecessor of Darkvision, in pre-3.0 editions of the game, loosely based on the premise of the ultra-violet spectrum, was essentially identical to Darkvision in all but name only. This attribute was usually only reserved for those races that lived exclusively in the dark or underground, such as the Drow (Dark Elves).
 * Infravision: Another predecessor of Darkvision, in pre-3.0 editions of the game, which was loosely based on the premise of the infra-red spectrum. It allowed some races to see in darkness by discerning the heat signatures left behind by other creatures. However, under the game rules description it was described as seeing in total darkness just as one would outdoors on a clear night under a bright full moon. This attribute was present in many demi-human races that lived above ground - such as the Elves (non Drow).

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. Often in the early editions this meant that an Armor Class of -10 indicted either intangibility (such as with incorporeal or ethereal creatures), or invulnerability.
 * In 3.0 and 3.5 editions, armor class instead starts at 10 and increases. Extremely non-dextrous or non-moving creatures may suffer penalties that lower their armor class below 10.

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. Typically beings fall unconscious at 0 HP. Living creatures reduced to negative HPs continue to lose additional HPs due to bleeding, etc. unless they are stabilized by chance or healing (natural or magical). At -10 HP a being is officially dead.

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 the pre-d20 System editions of D&D, there are five categories of saving throws:
 * '''Paralysis, Poison, or Death Magic
 * Petrification or Polymorph
 * Rods, Staves, Wands (magical devices)
 * Spells
 * Breath Weapons (such as with dragons or gorgons)

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 the 1st edition of the game, 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" or "creatures" pre se used the same as the generic fighter character type.
 * In the 2nd edition of the game, 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.
 * In 3.0 and 3.5 editions, the attack hits if the final result is equal to or greater than the target's Armor Class. Plain and simple.

Actions
The combat mechanic is turn-based and operates in rounds. A round is a discrete time interval (approximately 6 seconds, game-time) 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 2nd Edition of the game and continuing to the current 3rd Edition, has many skills that characters may train in. In the 2nd Edition these were broken down into Weapon and Non-Weapon Proficiencies. In the 3rd they are all simply referred to as "Skills", not to be confused with "Feats", below. 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 difficulty 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
A feat is an advantage, often some special option for the character (such as a special combat maneuver) or some modification to game options and the mechanics involved. Feats can be contrasted with skills, which were also introduced in the same edition, in that using a feat does not require the particular success/fail roll that skills do. Instead of possessing a certain rank at a skill, a character either possesses a feat or does not.

Many feats, especially the most powerful ones, require certain prerequisites (such as related feats or minimum ability scores) in order to select that feat. Some feats provide continual effects, while others, typically ones that have some cost to use or can be used to a variable degree, must be declared before use.

Feat types: Ambush, Bardic Music, Ceremony, Combat form, Epic, Exalted, Divine, General, Heritage, Item Creation, Metamagic, Metapsionic, Psionic, Reserve, Tactical, Weapon Style, Wild, Vile