Dark Coast dice pool

Dark Coast dice pool

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Mon Oct 24 16:05:49 2011   by   Torben
I'm working on a homebrew RPG called "Dark Coast".  You can find it at http://www.diku.dk/~torbenm/DarkCoast/.

Dark Coast uses a rather unusual dice-pool system.  As usual, ability (talent level) is measure as a number of dice, but unlike other systems, so is difficulty (challenge level).  The system is fairly simple: At talent level T and challenge level C, you roll T+1+C d6s, drop the T lowest and take the now lowest as the result.  Equivalently, you can drop the C highest and take the now highest as the result -- you get the same number either way.  The resulting number (between 1 and 6) is interpreted as a degree of success, with 1-3 being various degrees of failure and 4-6 being degrees of success.

With fixed C, the success chance increases with higher T and is exactly 50% if T=C.  But apart from the symmetric case, analysing probabilities by hand is not easy: Though you can find a closed formula for the probability of Nth-lowest of M dice being at least K, this is rather complex, so it is easier to use Troll.

In Troll, you can simply write

min largest (C+1) (T+1+C)d6

where T is the talent level and C is the challenge level. There is no operator in Troll for dropping the T lowest dice, so I instead keep the C+1 largest, which is the same when the total is T+1+C.  Equivalently, you can write

max least (T+1) (T+1+C)d6

which drops the C largest dice and takes the largest of the remaining.

If T>C, the first option is faster and if T<C, the second is faster: least and largest use time that increases quickly with the size of their first arguments, so you want to keep this small.

I have added the above as one of the predefined examples on the Troll page, so you can try it out.
Mon Dec 15 21:24:44 2014   by   Daniel
Hi Torben,

May you post some rolls examples of Dark Coast Mechanic? I don't understand whell...there are 2 dice pools in a single roll? One for Talent other for Chalange?
Tue Dec 16 11:44:22 2014   by   Torben
There is only one pool, but the number of dice is determined both by the Talent T and the Challenge rating C.  Let us say that a character with Talent 3 is attempting a task with Challenge rating 2.  We now roll T+1+C = 3+1+2 = 6 dice.  Let us say that the result of this roll is 1 3 3 5 5 6.  You now remove the T (i.e, 3) lowest and C (i.e, 2) highest results, leaving a result of 5.

Results of 1-3 are failures and 4-6 are successes, so this is a success.  With bonus effect even, as 4 is a normal success, 5 is a good success and 6 is an exceptional success.  Similarly, 3 is a normal failure, 2 is a bad failure and 1 is a horrible failure.

Another example: A character with Talent 1 is up against an opponent with Talent 3.  The Talent of the opponent is used as Challenge rating, so we roll T+1+C = 1+1+3 = 5 dice.  The result is 1 2 3 6 6.  You remove the 1 lowest and 3 highest results, leaving a 2.  So this is a bad failure.

A third example: A character with Talent 0 is attempting a task with Challenge level 0.  So we roll 0+1+0 = 1 die.  The result is a 4, so the character achieves a normal success.

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