The 3d20 system is the role-playing game system

Role-playing game system

A role-playing game system is a set of game mechanics used in a role-playing game to determine the outcome of a character's in-game actions...

 used in Neuroshima

Neuroshima

Neuroshima is a Polish tabletop roleplaying system inspired by such films and games as Mad Max, Fallout, The Matrix, Terminator and Deadlands: Hell on Earth. It is currently available only in Polish...

and Monastyr

Monastyr

Monastyr is a Polish role-playing game set in a dark fantasy world of Dominium.Its setting features a fantastic equivalent of the Age of Enlightenment. Most often, the game plays in a cloak and dagger mood and involves plotting, intrigue, but also struggle in the name of honour. The game has been...

. Like the d20 System

D20 System

The d20 System is a role-playing game system published in 2000 by Wizards of the Coast originally developed for the third edition of Dungeons & Dragons...

, it uses twenty-sided dice

Dice

A die is a small throwable object with multiple resting positions, used for generating random numbers...

, but unlike that system it most typically uses three.

Core mechanic

1. name the skill to be tested and the difficulty level
2. roll three twenty sided dice
   Dice
   A die is a small throwable object with multiple resting positions, used for generating random numbers...
   
   
3. compare all three separate results with the given attribute
   Attribute (role-playing games)
   An attribute is a piece of data that describes to what extent a fictional character in a role-playing game possesses a specific natural, in-born characteristic common to all characters in the game. That piece of data is usually an abstract number or, in some cases, a set of dice...
   
   
4. if at least two of the three results are lower than the attribute modified by the difficulty level, test is successful.

Details

When a test is required, the Gamemaster

Gamemaster

A gamemaster is a person who acts as an organizer, officiant for questions regarding rules, arbitrator, and moderator for a multiplayer game...

, names the skill which is going to be tested (or a raw attribute

Attribute (role-playing games)

An attribute is a piece of data that describes to what extent a fictional character in a role-playing game possesses a specific natural, in-born characteristic common to all characters in the game. That piece of data is usually an abstract number or, in some cases, a set of dice...

, if no skill is available for the activity the character

Player character

A player character or playable character is a character in a video game or role playing game who is controlled or controllable by a player, and is typically a protagonist of the story told in the course of the game. A player character is a persona of the player who controls it. Player characters...

 is trying to perform). He also sets a difficulty level for the test, which modifies the attribute value (reducing or improving it). Then, the character's skill level is taken into account - if the character does not have any skill levels in the given skill, (in case of Neuroshima

Neuroshima

Neuroshima is a Polish tabletop roleplaying system inspired by such films and games as Mad Max, Fallout, The Matrix, Terminator and Deadlands: Hell on Earth. It is currently available only in Polish...

) the difficulty level is raised by one, or (in case of Monastyr

Monastyr

Monastyr is a Polish role-playing game set in a dark fantasy world of Dominium.Its setting features a fantastic equivalent of the Age of Enlightenment. Most often, the game plays in a cloak and dagger mood and involves plotting, intrigue, but also struggle in the name of honour. The game has been...

), all the three rolls (not two) have to be lower than the tested attribute. Otherwise, the player can subtract a total of his character's skill levels in that skill from any of the three dice rolls, each separately.

Difficulty levels

Difficulty level	Attribute modifier	Difficulty level	Attribute modifier	Difficulty level	Attribute modifier
Easy	+ 2	Problematic	- 2	Very difficult	- 8
Average	0	Difficult	- 5	Extremely difficult	- 11

Special rules

• Suwak ("Slider") is a special rule of this game system. It says that when a character has at least four 4 levels in a skill, each time that skill is tested, the difficulty level is automatically lowered by one; if their skill level is 8 or 12, then difficulty is lowered by two or three levels respectively. It's supposed to depict the fact that the more trained a character becomes, the easier those things they trained seem to them.
• Lucky 1 - each time when making a test roll a player rolls "1" on any dice, he is lucky and manages to perform easily; in the terms of mechanics, the test is treated as if the difficulty level was lower by one. Notice: if the player rolls two "1's", the test is automatically successful.