The players use two d12 Duality Dice as their primary dice for action resolution, but as the GM, you’ll use one d20. This creates a less predictable outcome for your rolls, while the players will have more reliable results. You’re just as likely to roll abysmally high or low as you are to roll a middling number, whereas rolling two d12s creates a more stable bell curve of results. When you succeed, it creates a new and exciting challenge, and when you fail, it is a relief and a boon for the players. The swingy nature of the d20’s results helps facilitate a variety of outcomes during a session.

Making GM Rolls

When an adversary attacks a PC, you roll to determine the outcome. This follows a similar process to PC action rolls, except you use a d20 instead of two d12s:

Step 1: Calculate the Attack Roll

Roll your d20 and add the adversary’s attack bonus (along with any other dice, such as an additional d20 for advantage).

Step 2 : Determine if the Attack Hits

If the roll result meets or beats the target PC’s Evasion, the attack succeeds and hits the target. Otherwise, the attack fails and doesn’t hit.

Step 3: On a Hit, Roll for Damage

On a success, roll the appropriate damage dice to determine how much damage the attack deals.

If you ever want to increase the chances an adversary will succeed or fail, you can increase or decrease their attack modifier.

GM Critical Successes

PCs aren’t the only characters who can roll a critical success—their adversaries can too! Whenever you roll a 20 on the d20, your roll automatically succeeds.

If you critically succeed on an attack roll, you also deal extra damage. Start with the highest possible value the damage dice can roll, and then make a damage roll as usual, adding it to that value. For example, if the damage dice are 2d8+2 and you critically succeed on the roll, you would automatically deal 16 damage. You then roll the dice and get a 5 and a 7. So you add 16+5+7 for 28, plus 2 for the modifier, for a total of 30 damage.

A critical success on a reaction roll does not have any added benefit for an adversary.