List of core mechanics

[Morrus]

I'd like to make a list of core mechanics with a short description. Please add any you know of!

D20 System: used in D&D 3.x and variants, this at it's basic core is a roll of d20+modifier vs. a Difficulty Class. Rolling equal or above the DC is a success.

 

[Zhaleskra]

World Tree: Use a skill (or combination of skills) + d20 vs. a threshold , playing cards for initiative. In stressful situations, regular dice become stress dice and use the sN notation. Stress dice can explode or botch, they explode on their maximum (N) and can botch on a 1. Botch dice are d6s and only ones matter, the more ones the worse the botch. Botch? Roll on botch table according to severity and add effect to calculation. No botch? Just do the calculation. Succeeding too well (>= 30 over threshold) can cause "good with some bad", just as botching can lead to "bad, with some good" results. Combat is attack v. defense, both sides rolls, ties are broken in the defender's favor.

Pretty similar to d20 with a little more detail needed.

 

[Psychman]

BRP/RuneQuest and derivatives: Roll equal to or under listed skill rating on d100. Skill level may be modified for difficulty, usually by halving/doubling or adjusting up and down by units of 25.

Notable success/failure levels (critical/fumble) vary but critical usually either 10% or 5% of skill. If 5% a "special" success also exists at 20% of skill. Fumble can be 5% of failure or just 00 on the dice.

Opposed tests again vary, but popular option is known as "blackjack" where the higher dice roll in the same success category (success/critical) wins, reflecting the improved chances for the party with the higher skill rating. Higher success category (critical vs success) trumps this.

 

[Balesir]

HârnMaster core dice mechanic: skill and other rolls are percentile based. Roll d% with any roll greater than the target level a "Failure", any roll less than or equal to the target level a "Success". Any roll ending with a 5 or 0 is "Critical", all other rolls are "Marginal".

Degree or type of success is typically determined either by the number of "degrees of success" above the "defender" (e.g. Critical Success (CS) vs. Marginal Failure (MF) = +2 degrees better) or by a 2x2 matrix table of results.

One dice mechanic I have only seen in a wargame (De Bellis Antiquitatus and derivatives), but that I think has great potential for RPG uses:

Each side in a conflict rolls a die and adds/subtracts modifiers (including a base "skill" modifier). A result greater than your opponent is a marginal win (success), but a result double that of your opponent is a complete win (success).

This has the neat feature that a negative modifier to your opponent is very different in implications than a positive one to yourself, and the absolute magnitude of the net modifiers is relevant as well as the relative magnitudes (i.e. a +5 vs a +4 is very different from a +2 vs a +1).

 

[Sword of Spirit]

Maybe we need a sub-forum for game design and theory?

 

[Ahnehnois]

Cortex: Used in Serenity, Battlestar Galactica, Cortex Generic. Roll two dice of varying size; one for ability and another for skill. If the result matches or exceeds the Difficulty, the action succeeds, otherwise it fails.

 

[howandwhy99]

Early D&D doesn't really have one core mechanic, but several are central. I think there is one very central relationship though. That's the linear progression die roll with a bell curve (or more rightly parabola) of represented results. You can find this in the first few pages of the AD&D DMG.

It uses this stepped progression in all sorts of areas besides just d20 rolls overlayed by 3d6 stats. The classes and XP charts (sort of) increase logarithmically. The world increases so too with a step ladder of challenge results by region, but each of those levels in AD&D are populated by a bell curve of challenges. So each has the balance maintained for its level, yet includes a broad variety of challenges within it.

 

[Hyper-Man]

Here is the basic Hero System mechanic from: Hero in 2 Pages

Dice Rolls
Hero System uses two kinds of dice rolls.

The first is a Success Roll . In a Success Roll, you roll under a number on 3d6 (three six-sided dice). A total of 18 is always a failure; a total of 3 is always a success. Success Rolls are displayed as X-, such as 12- for “Roll 12 or under on 3d6”. The lower you roll under, the better.

The second is an Effect Roll . In an Effect Roll, Xd6 is rolled - That is, an arbitrary number (3, 5, 8, whatever) of six-sided dice. Effect rolls may be counted in two ways:

Counting the BODY: Count the number of dice. Subtract any 1’s rolled; add +1 for any 6’s.

Counting the Total: Simply total the die roll.

1/2 d6 is half the result of a d6. For BODY, that means a roll of 4-6 is +1 and 1-3 is 0. For a Total roll, 1-2 is +1, 3-4 is +2 and 5-6 is +3.

+1 is just that - “Add +1 to the Total”. Effects of +1 adds no BODY. Counting Killing BODY Damage is the only exception.

 

[howandwhy99]

You tell a story, I tell a story, we make up that they are in conflict, and come to agreement on whose story will be included in the group's story.

I believe that's the core mechanic of most story games.

 

[CarlZog]

Alternity: Roll 1d20 ("control die") +/- one other "situation" die (d0, 1d4, 1d6, 1d8, 1d12, or 1d20) vs. an ability or skill rank. Roll less than the ability or skill rank to succeed. The lower the roll below the target number, the greater the degree of success; the higher the roll above the target, the greater the degree of failure. The task difficulty and its circumstances are wholly reflected in the choice of situation die and whether it is subtracted or added to the d20 control die, creating a range of "situation die steps" from a bonus of -1d20 to a penalty of +1d20 (or more for absurdly difficult tasks).