Designing a Roll Under System
(or, I Don't Generally Design Pass/Fail Systems, But When I Do...)
Conversation over on the 'Sky the other day about roll over systems (D&D) vs roll under systems (Cairn). I tend to prefer roll over mechanics for reasons that can be best summed up as "vibes". But one part about roll under mechanics that never quite clicks for me is that many of them are fixed target numbers regardless of the difficulty of the situation. Those that don't tend to get messy quickly. So I started thinking about how I could make something work that has the simplicity of a personal, fixed, roll under target number but also doesn't fall apart the second you adjust for difficulty. So here we go:
You have Stats. These are fixed numbers out of 20.
You have Traits. These are personal qualities that describe you.
When you attempt a challenge, compare your relevant Traits with the Traits of the challenge.
*If you have equal Traits, roll a d20 and succeed if you roll under your Stat
*If you have 1 more Trait, roll with advantage
*If you have 1 less, roll with disadvantage
*If you have 2+ more Traits than the challenge, the attempt succeeds automatically
*If you have 2+ fewer, the action is impossible
There it is. That's the system.
Okay, an example? Sure.
You want to kick open a door. The door is Locked, Sturdy, and Heavy. You are Athletic and Well Built. You would roll your Stat at disadvantage.
But! What if you have room to Take a Running Start? Are you Willing to Make a Lot of Noise? Perhaps you can gain a situational Trait for this challenge that might make things easier.
Example the second:
You want to sneak past a guard. The guard is Dutiful and Alert. The hallway is Well Lit. You are Stealthy and wearing Soft Shoes.
You could cause a Distraction. You could do something to the torches so the hall is no longer Well Lit.
I'm probably not going to make a game around this (I'm working on two other systems already), so I release this into the wild. Go and make something with this engine if you like. If only I could think of a snappy name for it.