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Monday, 7 May 2018

D12 System Dev Diary 1

What's all this about?

This work is directly inspired by both Evil Hat's Fate Core and John Harper's excellent Blades in the Dark. Indirectly by a 30+ year history of analogue and computer gaming. I was looking for something to use for an open world FRPG and although I love both Blades and Fate, neither was quite the right fit for the feel of the game I want to run. So what started as a Fate/Blades hack has become something rather more. This version  unashamedly uses a bucketload of d12's because they give the results curve a nice shape and they roll nicely.

I wanted to retain player agency so similarly to Blades only the players roll dice in most circumstances. There's going to be all manner of conflict in this game and so I wanted to generate a feel of dynamism which I'm hoping to do with advantages.

Taking action

There is no need to make an action test if:
  • an action has no reasonable chance of failure
  • failure would not produce an interesting  complication 
  • failure would not move the story forward
  • failure does not add dramatic tension
In any of these cases the action should be narrated as having succeeded without rolling dice. Otherwise, an action test is required
  • Build a dice pool
  • Split the pool into action and reaction dice
  • If you act first the roll action dice and check the result
  • If you need to make a reaction roll those dice and check the result

Building your pool

  • Start with a number of dice equal to your ability.
  • If your aptitude applies add 1D
  • Use an advantage to add 1D
  • If the action is above your ability then subtract 1D
  • For each complication subtract 1D
  • When an opponent has the advantage subtract 1D
  • Physical actions add 1D and have a minimum pool of 1D
If the action is directly opposed then split your pool into action and reaction dice.

You will usually have a choice of whether to act or react first but sometimes circumstances will dictate who acts first.

Rolling the dice

Roll all your (re) action dice. Highest number counts.

If your highest result is:
  • 1-3 you flub your action in the worst possible way and probably give your opponent the advantage.
  • 4-6 things are not going your way. you fail to achieve the outcome you wanted.
  • 7-9 glass half full. you managed to do it but at a cost.
  • 10-11 done deal. your action plays out exactly the way to wanted.
  • 12 stylish. success with flair, increased effect, start a chain or +1 advantage.
If your top result is 10-12 then for every extra 10-12 result you get you gain +1 advantage.


Advantages come in two flavours, immediate and perpetual.

Immediate advantages are usually the result of action test rolls and can be spent on the task at hand only. They can not be carried over to new tasks, although they may be carried over to different types of actions that are part of the same task where appropriate.

Immediate advantage is lost when:
  • The task at hand has finished (complete or otherwise)
  • It is spent on actions to accomplish the task at hand.
  • When it is squandered (a 4-6 max result)

  • When it is taken from you (a 1-3 max result)
Perpetual advantages are usually gained from equipment, training, secret knowledge, magic or other means. They can be used on multiple tasks and often on multiple actions in a task.

Using your advantage

Advantages can only be applied to actions following the action that generated them. 

They can be used before the roll for +1D each
They can be used after the roll to buy up a result on 1D, e.g. turning a 1-3 result into a 4-6 result etc.
If you buy up to a 12 result then that result does not generate advantage but may be used for flair, increased effect or to start a chain.

That's it for D12 Dev Diary 1, next up some worked examples and a touch of world building.

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