Actions and Reactions

In my previous post I listed modular, simple and elegant, and promoting rulings not rules as my goals for a skill system. I still think they're great goals, but quite abstract. At a more concrete level I want a system where

• a player making a character can write down (or roll up) a short list like "sailor, dirty tricks, goblin lore" and proceed to play, 

• a character A having a skill "riding" does not mean that character B is hopeless at staying on a horse,

• skills and combat are separate systems, but that allows skill use during combat, i.e., for grappling,

• skills and classes are separate systems, but that allows characters to pick up skills as one of the benefits of being a particular class,

• it can be be a light-weight addition to a D&D ruleset such as BX / Labyrinth Lord or OD&D / Swords & Wizardry.  

So here is my attempt (commentary follows afterward). It uses dice steps with a dice progression d3 -> d4 -> d6 -> d8 -> d10 -> d12 -> d14 (sorry) -> d16 -> d20, etc.

Basic Rules

When characters attempt an action whose success is uncertain, or to react in a way that will save themselves or prevent another’s action, the success or failure of the attempt is determined by an action check. First the player describes what the character is trying to do. The GM will consider which ability is most likely to help the character succeed (the governing ability) and whether any of the character’s skills would make the character significantly better at accomplishing the action (a relevant skill). The GM then considers how hard the action would be to perform, and assigns it a difficulty rating to reflect that. Finally, the player rolls one or more action dice, and if the result (the highest die rolled) is equal to or higher than the difficulty rating, then the action succeeds.

Yes, you do need to check to fly
standing up.

Action die: Characters have a base action die which is d8 at level 1 and improves at higher levels and for some classes. The die step is adjusted up or down by the modifier of the character’s governing attribute. Finally, the die step is adjusted upward by 1 if the character is an expert in a relevant skill or by 2 if the character is a master in a relevant skill.

Action die size = (base action die) +  (governing attribute bonus steps) + (governing skill mastery steps)

Governing ability: see ability scores for a description of each ability's applications.

Roll strength!

Relevant skill: the GM should construe skills broadly. Example: a hunting skill would be useful for successfully hiding outdoors, if that is a hunting method the character might know.

Number of action dice: characters without a relevant skill in the action, or attempting an action for which there is no governing skill, roll 1 die. Characters with a relevant skill roll 2 dice.

Difficulty rating: the standard difficulty rating is 8, which reflects a challenging but not impossible action. Most actions the characters undertake should be like that! An extremely unlikely action's difficulty can be adjusted upwards to 9 or even 10, but the GM should make these adjustments infrequently. Extra preparation on the part of the character, advantageous circumstances, or help from another character can reduce the difficulty rating to 7 or even 6. Actions that would be difficulty 5 or less should normally be treated as automatically successful.

Result: the highest number rolled on any action die is the result of the attempt. The GM gauges success or failure by the result, and ignores any other numbers rolled.

Success: if the result is at least as high as the difficulty rating, then the action succeeds. Another check is not necessary unless the situation changes dramatically.

Partial success: a result 1 to 2 less than the difficulty rating indicates success, but with some complication. The character succeeds in the action, but the success inconveniences the character somehow. The GM determines the exact complication that the character faces. Example: Bianca attempts to jump onto a ledge across a chasm and rolls a partial success. Her feet slip, but she grabs the ledge with her hands. Next round she must pull herself up.

Failure: a result of 3 or more less than the difficulty rating indicates that the action was totally unsuccessful. Another check may not be attempted unless the situation changes dramatically.

Reactions: many RPGs have saving throws to avoid or mitigate perils that the character faces. The action and reaction system can replace saving throws. When the GM would call for a saving throw, she should describe the danger to the players and ask what their characters are doing to avoid the danger. Based on each response, she should resolve the character’s action to avoid the danger. A successful reaction save may not prevent damage entirely.

Opposed rolls: when one character opposes the action of another character, as in arm-wrestling or hiding and tracking, they make opposed rolls. The GM determines the action roll for each, as above, and then both make rolls. The character with the higher result succeeds. If both results are the same, the contest deadlocks or both fail, as determined by the GM. If a character suffers a critical failure, that character suffers some additional adverse consequence beyond failure. Likewise, if a character achieves a critical success, that character’s success is exceptionally large.

Group actions: in some circumstances, a group of characters is attempting an action in which the entire group will either succeed or fail as a whole but more skilled characters might be able to help the less skilled. In this case, the group's attempt is resolved by having the character with the lowest action die and and other single character (chosen by the players) both make action checks. If neither fails, then the group has succeeded; if one fails, then the group has achieved a partial success; and if both fail, then the group has failed.

Examples

Cedrick the warrior attempts to a lift a gate that has crashed down behind the party. He has 16 strength so adjusts his d8 action die to a d12. "Hey, I have endurance skill. That should be relevant shouldn't it, because it'll help me strain to lift the gate?" asks Henry, Cedrick's player. "Sure," says the GM. Henry rolls 2d12 and gets a 1 and a 9. "Standard difficulty, right?" "Yup." Cedrick succeeds with a result of 9.

Warwolf, Cedrick, and Gesaine have been chained together by the ankles by bugbear slavers. While the bugbears are marching the characters down a forest path, Gesaine distracts the bugbears with her ventriloquism. As the bugbears investigate the suspicious noises behind them, the three characters attempt to run off. The GM calls for a group action check using dexterity. None of the characters have relevant skills, and while Cedrick and Gesaine both have dexterity 15, a plus one step modifier, Warwolf has dexterity 10. Gesaine's player rolls a d10, getting a 6, while Warwolf's player rolls a d8 and gets a 3.  One failure and one non-failure means that the group has partially succeeded. The GM rules that the characters make it to the tree line before one of the bugbears makes a hue and cry. All of the slavers begin to chase the characters and have almost caught them, but then the characters slide down a cliff to the bottom of a 50' crevice, remarkably not hurting themselves in doing so. Bugbear heads stare down at them from the top of the cliff.

Commentary

The basic system has three free parameters: the base action die size, the standard difficulty rating, and the number of dice a skilled character rolls. The current system is based on fiddling around with these parameters for a couple of hours. The numbers above represent a world in which level 1 adventurers are relatively competent even when unskilled and quickly grow to succeed more often than not. A level 1 thief with a 14 dex and skill at sneaking would succeed at moving silently at least partially 75% of the time (action die d10, 2 rolls, need 6+ for partial success so 50% chance on each die). That may be too generous; maybe a 8+ standard difficulty rating would be better.

One nice aspect of the system is how skills interact with its other components: partial success, ability modifiers, opposed rolls, and group actions.

First, skills are reliable. A character attempting an action for which she does not have an attribute bonus and who also has no relevant skill will succeed completely in 12.5% of her attempts, and partially in 25% of her attempts. If she has a relevant skill, she will succeed completely in 24% of her attempts and partially in 38% of her attempts. Total failure becomes much less likely.

Second, skills complement a character's strengths. Raw ability only gets a character so far. A character free-climbing a wall with 10 strength has a 62.5% of failure. A stronger character with 15 strength reduces her chance of failure to 50%, or by 12.5%, and even higher strength 16 reduces her chance of failure to about 42%, or by 8%. Add climbing skills to the mix, and moving from 10 strength to 15, and 15 to 16, decreases failure from about 39% to 25%. Attributes and skills are both important in ways that I find satisfying.

Skills are also especially important with opposed rolls. If two otherwise identical characters face each other in an opposed roll but one is skilled, the skilled character succeeds 75% of the time, so being skilled are very useful in opposed rolls. On the other hand, a naturally talented character can through luck overcome a skilled but less talented character. For example, character A has 11 str and is skilled at wrestling, while character B has 15 str but no skill. 1/5 of the time character B will roll a 9 or 10 and win, but the remaining 4/5 of the time both characters are equally likely to roll 1 through 8 on each of their action dice, in which case character A has an 75% chance of winning. Overall, character A has a 60% chance (4/5 * 3/4).

Finally, skills also play the natural role in group actions of making a big difference for the team. Having a skill makes it much less likely that a character will fail a check outright, so having a skilled character involved in the group check makes it likely that that group will partially succeed at least, as is likely if the characters are helping each other accomplish the task.