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Ars Arcana Blog: Split Die Pools / Multiple Actions



Split Die Pools / Multiple Actions
Travis Joseph Rodgers

The Dungeon Chatter system uses a d20 base roll with a modifier of XD6. So a roll at "minus 3" means that you're rolling 1d20 minus 3d6. A "10" is always a success, a negative number is always a critical failure, and a 20 is always a critical success.

I've just introduced rules for split die pools. I've done it with the following three rules:

Rule 1. Skill Required
Your relevant skill must be above 0. A zero represents familiarity but lack of skill, so if you're only familiar with something, you can't try to trade off skill for speed/frequency.

Rule 2. Buy Frequency /Spend Skill
You can double your actions (from 1 to 2) by rolling each check at two less than your total pool.
So, if you have a +3, you can roll two +1 actions (+3 - 2 = +1).
If you have a +2, you can roll two +0 actions.
If you have a +1, you can roll two -1 actions.
You cannot roll two actions if you have below a +1 (see rule 1).

Rule 3. The Process is Iterative
So, if you have a +3, you can make two +1 rolls. But since for each +1 roll, you can make two -1 rolls, you could translate your +3 into:
a single +3 roll
one +1 roll and two -1 rolls
four -1 rolls

With those rules in mind, I started thinking about when it made sense to split your die pool. Would it always or never make sense?

Here's the breakdown:
One at +3 vs. two at +1
97% Success% 93%
3% Fail% 7%
48% Single Crit% 41%
0% Single Crit Fail% 0%
0% Two Success% 53%
0% Two Crit% 5%
A +3 roll gives an exceptionally good chance of success and a good shot at a critical. It's "safe" in that a check will never critically fail.

The two +1 rolls drop the success chance and the odds that the roll will result in a critical, but it opens up the possibility of two successes and a slim shot at two criticals.

The +3 is probably best for foes with lots of armor, while the +1 is probably best for multiple foes or foes with light armor. Confession: I really like this aspect of the system.
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