Using Ability Scores

Six abilities provide a quick description of every creature’s physical and mental characteristics: Is a character muscle-bound and insightful? Brilliant and charming? Nimble and hardy? Ability scores define these qualities—a creature’s assets as well as weaknesses.
 * Strength, measuring physical power
 * Dexterity, measuring agility
 * Constitution, measuring endurance
 * Intelligence, measuring reasoning and memory
 * Wisdom, measuring perception and insight
 * Charisma, measuring force of personality

The three rolls of the game—the skill check, the ability check, the saving throw, and the attack roll—rely on the six ability scores. The book’s introduction describes the basic rule behind these rolls: roll a d20, add an ability modifier derived from one of the six ability scores, and compare the total to a target number.

Ability Scores and Modifiers Edit
Each of a creature’s abilities has a score, a number that defines the magnitude of that ability. An ability score is not just a measure of innate capabilities, but also encompasses a creature’s training and competence in activities related to that ability.

A score of 10 or 11 is the normal human average, but adventurers and many monsters are a cut above average in most abilities. A score of 18 is the highest that a person usually reaches. Adventurers can have scores as high as 20, and monsters and divine beings can have scores as high as 30.

Each ability also has a modifier, derived from the score and ranging from −5 (for an ability score of 1) to +10 (for a score of 30). The Ability Scores and Modifiers table notes the ability modifiers for the range of possible ability scores, from 1 to 30.

In OCD&D each ability score creates a primary, and a secondary ability score modifier, and while the primary modifier is the most commonly used, the secondary ability modifier comes into play in certain circumstances (described throughout).

Because ability modifiers affect almost every attack roll, ability check, and saving throw, ability modifiers come up in play more often than their associated scores. See the section on Ability Scoresfor an overview of ability scores and modifiers.

Advantage and Disadvantage Edit
Sometimes a special ability or spell tells you that you have advantage or disadvantage on an ability check, a saving throw, or an attack roll. When that happens, you roll a second d20 when you make the roll. Use the higher of the two rolls if you have advantage, and use the lower roll if you have disadvantage. For example, if you have disadvantage and roll a 17 and a 5, you use the 5. If you instead have advantage and roll those numbers, you use the 17.

If multiple situations affect a roll and each one grants advantage or imposes disadvantage on it, you don’t roll more than one additional d20. If two favorable situations grant advantage, for example, you still roll only one additional d20.

If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.

When you have advantage or disadvantage and something in the game, such as the halfling’s Lucky trait, lets you reroll the d20, you can reroll only one of the dice. You choose which one. For example, if a halfling has advantage or disadvantage on an ability check and rolls a 1 and a 13, the halfling could use the Lucky trait to reroll the 1.

You usually gain advantage or disadvantage through the use of special abilities, actions, or spells. Inspiration can also give a character advantage. The Not for resale. Permission granted to print or photocopy this document for personal use only. System Reference Document 5.1 77 GM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result.

Proficiency Bonus Edit
Characters have a proficiency bonus determined by class and level. In OCD&D there are three proficiency levels, low medium and high.

Proficiency Bonus based on level and proficiency: In some cases your level of proficiency may increase (usually from taking a feat or a class ability). If this happens just consult the table to find the new proficiency bonus based on your level.

In cases where the character is not proficent, the "proficiency bonus" is -2 regardless of level.

Monsters also have this bonus, which is incorporated in their stat blocks. The bonus is used in the rules on ability checks, saving throws, and attack rolls.

Your proficiency bonus can’t be added to a single die roll or other number more than once. For example, if two different rules say you can add your proficiency bonus to a Wisdom saving throw, you nevertheless add the bonus only once when you make the save.

Occasionally, your proficiency bonus might be multiplied or divided (doubled or halved, for example) before you apply it. For example, the rogue’s Expertise feature doubles the proficiency bonus for certain ability checks. If a circumstance suggests that your proficiency bonus applies more than once to the same roll, you still add it only once and multiply or divide it only once. If a feature or effect allows you to multiply your proficiency bonus when making an ability check that wouldn’t normally benefit from your proficiency bonus, you still don’t add the bonus to the check. Finally the "proficiency bonus" for having no proficiency in remains -2 regardless of any multiplieers or dividers that may be applied.