Botch die
When failing a die roll in stressful situations, that is, if a Stress Die comes up with a 0, players usually have to roll a certain number of botch dice for their characters. The number of botch dice that have to be cast is usually not set in stone, but is assigned by the Story Guide according to the situation.
Reading the Botch Dice
Botch dice are 10-sided (just like all dice in Ars Magica). Reading them is simple: if any botch die comes up zero, a Botch has occurred. If more than one botch die is zero, this is called a "double botch," "triple botch," and so forth.
The effects of a botch are generally left up to the Story Guide.
Number of Botch Dice
Different editions of Ars Magica give different guidance on how many botch dice should be rolled under particular circumstances. These are always presented as suggestions rather than strict rules.
Earlier editions of Ars Magica generally recommended more botch dice than does ArM5.
Certain virtues and flaws modify the number of botch dice, as do some Abilities, such as Spell Mastery. The number of botch dice for magical effects is influences by the magus's bond with his familiar, the prevailing supernatural Aura, and so on.
Botch Chance Table
Ars Magica Fifth Edition contains a table showing the probability of a Botch according to the number of botch dice. The purpose of this table is simply to help players get a feel for how the chance of a botch increases with the number of botch dice. The numbers on that table are not meant to be used during play!
For those who are interested, the Botch Chance table was calculated using the binomial distribution.
References
- Botch Dice, ArM5 page 7.
Legacy Page
The history of this page before August 6, 2010 is archived at Legacy:botch_die