Time to use this account for the purpose I actually made it for.
I came up with this idea while thinking about how many Roll to Dodge GM's implement skills and difficulty by adding or subtracting to the result of the dice. I've never liked this idea because it's tricky to fit rolls like 7 or -1 into the RTD rules in a consistent way.
So I came up with these rules that change the chances that the player will get a particular roll, rather than changing the roll itself.
Rules:
Single dice are interpreted according to normal Roll to Dodge rules.
All dice are d6.
However, the number and "type" of dice rolled is modified by skills, difficulty and other context, similar to Cogent's "challenge level" mechanic.
Each action that is rolled for (i.e. not a free action) uses at least one die - exactly one normal die corresponding to the one die in normal RTD, plus possible bonus or penalty dice.
There is always one, and only one, normal die for an action.
If the GM rules that an action is more difficult than usual because of extra difficulty, negative status effects, or other conditions at the GM's discretion, an amount of penalty dice are added to the group of dice being rolled for that action. (I should probably call them something different, because they represent harmful conditions in-game, rather than being penalties applied to a player for punishment. Though the GM could do that, certainly.)
If the GM rules that a character has an advantage at performing an action due to character skills, helpful status effects, or other conditions at the GM's discretion, an amount of bonus dice are added to the group of dice being rolled for that action.
The group of dice is then interpreted as follows:
1. The number of penalty and bonus dice are counted and each pair of penalty and bonus dice "cancel" each other out, and each pair is removed form the group, essentially subtracting the smaller group from the larger. For example, if an action required 3 penalty dice, one normal die, and 2 bonus dice, the resulting group would be:
1 normal die and 1 penalty die (3 penalty dice - 2 bonus dice = 1 penalty die.)
2. Every remaining die in the group is rolled.
If there is only a single die, its roll obviously is the one that counts towards the action, and is interpreted with normal RTD rules.
If there is more than one die, the roll that counts is the lowest roll if the extra (non-normal) dice are penalty dice, and it is the highest roll if the extra dice are bonus dice.
Various examples:
- 2 penalty dice, plus the one normal die, are rolled. The penalty dice rolled 3 and 4, and the normal die rolled 5. The roll that counts towards the action is 3 because the lowest roll counts if there are penalty dice.
- Same as above except the normal die rolled 2. The role that counts is the normal die's 2 because penalty dice can't replace the normal die with a higher roll.
- 2 bonus dice, plus the normal die, are rolled. The normal die rolled a 1, but the bonus dice rolled 2 and 5. The 5 counts because the highest roll counts if there are bonus dice.
So, what are your thoughts on this system, as players and GM's? Ease of use? Balance? Any other comments?
EDIT: made description of the normal die more clear.