The system is very simple, when the success of an action is uncertain
(and only in this case, RPG isn't Roll Playing Game) you should roll a dice
for deciding of the action result.
For a skill (or sometimes a Primary attribute) to be used successfully the roll of a D20 must fall lower than or equal to the level of the skill (or attribute).
A roll of 1 is always a success if you are familiar with the skill.
A roll of 20 is always a failure.
A roll of 20 is a critical failure if you are not familiar with the skill.
A roll of 20 and a failure on a second roll is a critical failure if you are familiar with a skill.
If the roll is 11 or more higher than your level, it's a critical failure.
If the roll is 11 or more lower than your level, it's a critical success.
A critical success is a very favorable result, and a critical failure is a catastrophical result
Sometimes an action is more difficult or easy than normal, the GM could
assign a bonus or penalty to any roll.If the penalty is -25 or more the action
is an automatic failure (have you ever tried to shoot at a rabbit when you are
bleeding in an unstable helicopter flying at 250 mph within a night fog ?).
Here is a list of common modifiers for tasks.
|Very Easy||Automatic success|
Clark is climbing a mountain, he 's got 12 in Climbing. The GM thinks it's a hard task so he assigns a skill modifier of -5 ( Clark will succeed with a roll of 7 or less). Clark roll the dice: it's 18, a critical failure! Clark, who didn't think about a rope is falling at the height of several hundred feet. All we can say is goodbye Clark...
Sometimes a character prevent another character from succeeding at a task
by opposing it directly.The character prevent the action by succeeding an
appropriate roll.For example to resist an interrogation, a character should
succeed with a roll against his Will.
To prevent a critical successful action, the opposed character should get a critical success too.
Sometimes two characters are competing each other (like a chess game,
a car race or a cooking contest). This is called a competition
roll.In this case the two characters roll under the same skill or attribute.
The winner is the character with the best success margin.If the success
margins are the same, it's a draw.
For example John and Clark are playing a chess game, they have a chess skill of 14.John rolls 6 (a difference of 8 with his skill level), and Clark rolls 10 (a difference of 4).The winner is John as he got a better success level.