Open-Ended Die Rolls
Die rolls where some results indicate making more die rolls to achieve the final result.
Dice are used in many games to create randomness. The range provided by the dice does however give a fixed interval of which results can be achieved before the roll is made. This can be avoided by letting certain results, e.g. a 6 on a 6-sided die, signify that additional dice should be rolled to create the random value. This makes the upper bound (since added dice are typically used to increase the result) of the die roll open-ended.
The D6 System by West End Games has one wild die for damage rolls and checks against skills or attributes. When a 6 is rolled on the wild die, another wild die is rolled to generate the result, and this can potentially continue for ever.
The first edition of Warhammer Fantasy Roleplay used Open-Ended Die Rolls for damage but required an additional success with a character's weapon skill to unlock the open-endedness if a 6 was rolled. This made it more probably for skilled fighters to do exceptional damage than unskilled ones.
Using the pattern
The two main design choices regarding Open-Ended Die Rolls is what results trigger additional dice rolls and which rolls and dice the mechanic affects. The most common solution is that the highest result, i.e. a 6 on a D6 and a 20 on a D20, activates new rolls but adding more result increase the frequency with which the pattern manifests itself and the minimum can be used to create fumbles or critical failures. For cases where many dice are rolled initially, limiting the open-ended mechanic to one die is a way to not make the pattern occur too often (e.g. allowing additional die on any 6 on a 3D6 roll gives a 42% chance that at least one more die will need to be rolled). Open-Ended Die Rolls are most typically used for rolls against Attributes or Skills in Tabletop Roleplaying Games, and can be limited to Player Characters to make them exceptional compared to other Characters.
A specific issue with Open-Ended Die Rolls is that simple additions of extra dice have the effect that some values may not be possible to generate. For example, a Open-Ended Die Roll with a single D6 that triggers on a 6 can produce values between 1 and 5, 7 and 11, etc. but not 6, 12, 18, etc. This can be mitigated by modifying the result of each extra die with a -1 but this does make calculations more cumbersome to do mentally.
A weaker form of Open-Ended Die Rolls can be created by putting constraints on how many times dices can be added; this provides an upper bound but still achieves the effect of having some results be rarer and more exceptional.
An alternative to Open-Ended Die Rolls is Critical Results.
Open-Ended Die Rolls allow for luck or misfortune to manifest itself in the game world through gameplay mechanics. This can however also be done through Critical Results.
The adding of Open-Ended Die Rolls can tax players mathematical abilities, especially if fixes have been inserted to give result intervals without holes.
Open-Ended Die Rolls can produce Exceptional Events and by this can let players hope for Luck; mirroring this, the pattern makes Dice rolls have less Predictable Consequences. When the work to produce and calculate the final value becomes non-trivial, the pattern can produce Exercise.
Can Be Instantiated By
Can Be Modulated By
Possible Closure Effects
Potentially Conflicting With
New pattern created in this wiki.
- Wikipedia entry for the D6 system.