11 September 2022

Coriolis RPG skill check probabilities

In Coriolis the skill rolls use a pool of d6, and you count how many 6's you rolled, a 6 is considered a success. You can optionally reroll any dice that were not 6's the first time you rolled. Sometimes you can add bonus d6 dice to the reroll pool. If you roll more successes that's good, if you roll 1 success that's a 'limited' success, if you roll 3 or more it's a 'critical' success.

I wanted to model this probability as the book only shows the chance of rolling a success and one reroll, but doesn't mention if that reroll had any extra bonus dice.

With some help from a kind internet stranger here is the anydice statement to get the probabilities of rolling 1, 2..10 dice with a bonus of B extra dice on the reroll.

B:0
loop N over {1,2,3,4,5,6,7,8,9,10}{
output [count 6 in Nd{1d6:5, 6:6}]+[count 6 in Bd6]
}

Here is a table of results, for 0, 1, 2 or 3 bonus dice and showing for a limited success and critical success:

Limited successes chart













Critical successes chart

























Prayer reroll bonus rules in the Core Rule book

  • Ship Chapel (p147) "grants +1 to the prayer reroll for the whole crew"
  • Preparatory prayer (p55) "you must make time before you jump into the fray, grants +1 to rerolls to the same Icon for that session"
  • Preparatory prayer in a Chapel (p56) "you must make time before you jump into the fray, grants +2 to rerolls to the same Icon for that session"

Prayer reroll bonus rules interpretation

  • +1 any skill: The ship you crew has a Chapel 
  • +1 same icon: You made time for preparatory prayers to a specific icon
  • +2 same icon: The ship you crew has a Chapel AND You made time for preparatory prayers to a specific icon
  • +2 same icon: You made time for preparatory prayers to a specific icon in any chapel
  • +3 same icon: The ship you crew has a Chapel AND You made time for preparatory prayers to a specific icon in any Chapel

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