Mechanics for chance roll

Any advice on how to roll for a typical chance roll of pure serendipity (i.e., not linked to any skill / drive or even character), but taking into account some degree of likelihood of the event?

It’d be neat to have a system for this where GM and players can use their respective momentum / threat point to influence. Like, let’s roll to see if a patrol is coming… Any mechanics to draw from other 2d20 games on this?

Perhaps setting the bar at 10, and rolling 2d20 at difficulty 1 for a 50/50 roll, difficulty 2+ for less likely happenstances, and letting the players / GM use momentum / threat to add or remove dice to that.

Could you give some examples for such situations where you want do decide things by a roll, but not as an action, not relying on character abilities?

Things like, “a patrol is coming” is to be decided by the GM at whim or due to some dramatic necessity, mechanically usually combined with spending some Threat or leveraging a Complication rolled by the PCs some time before that.

I’m not sure why there has to be a roll in the first place. Dune 2d20 is a very strongly narratively based RPG, which is governed by dramatic directions, not so much by simulation of a fictional “reality”. That is why the GM has the Threat resource in the first place. To allow for the ups and downs of the flow of tension in the narration.

If you really want a roll the players might have an influence on, then maybe let some PCs (like a Mentat or Bene Gesserit who are well known for being prepared for anything) make a test using an appropriate Drive and maybe the Understand skill, to check the general preparedness for something developing (like a patrol showing up). On that test you can spend Momentum or Threat as usual.
Though, still, I wouldn’t use any kind of die roll at all, simply spend some Threat and things happen.

Yeah. My example wasn’t great. But I don’t think it’s a narrative vs. non narrative RPG issue though. For example, there are many things in FitD system that can be resolved with a 0 risk “chance” roll by using a tier (money, faction tier, item tier, etc.).

The real use case is this: every now and then, a player asks a question of pure externality like “is character so and so at the party tonight?”, “can I find this type of item lying around?”, “is such and such faction aware of fact XYZ?”, etc.

Fiction-wise, the GM wants to say no, but unless the question is “can elephants fly?” any good GM knows that it’s not the right way to move the action forward for the players, and most modern games have a clear way of dealing with this, either by having a consequence-based response (e.g., a flashback with cost to have such item in FitD) or a “chance roll” (e.g., a roll based on no characteristics with modulable difficulty to give a chance for an outcome).

Here, it feels to me that the answer in the spirit of the game would be to have the players use momentum to create a trait or asset that matches what they want. But I am also wondering if there a concept of chance roll that’s well defined somewhere, if not in Dune in some other 2d20? The alternative is that the GM has to be able to plainly say “no” based on fiction, even if there is a remote chance that the answer could be yes. But honestly that would be a gap in rules in my eyes.

And sorry. My reply reads more combative than what it’s meant.

I guess I’m still on my pointed question:

Is there such a thing as a « chance roll » in any other 2d20 games as far as people know?


I play mostly Star Trek Adventures as 2d20 game, but there is also not a pure “chance” mechanic. Agreeing with @FrankF, I also don’t see the need for this. Going purely by your examples I’ll try to explain how I would handle these situations as a GM:

“is character so and so at the party tonight?”
Depends on why the player asks. If they have a good idea and the NPC could realistically be at that party, then I simply say the NPC is at the party because it will make for a good story. Maybe the PC has to do a test to find out that information though.

“can I find this type of item lying around?”
Sure, spend 2 Momentum to create an Asset.

“is such and such faction aware of fact XYZ?”
Make a test to Obtain Information.

This is how the system is designed. If you are unsure as a GM whether to allow something or not you can of course just flip a coin.

I always try to answer those questions in a manner that makes the most logical sense and produces the best story.

In Conan, players can spend Fortune (which is somewhat similar to Determination) to influence the story. But that’s no chance roll either.

I’d agree its a thing each GM can sort for the needs of their group.
I rather like allowing players to throw things into the plot
“Is NPC Bob there?” “Maybe, you tell me.”

But I do also roll a dice for ‘How annoyed is this NPC’ or ‘How crowded is the shop’ etc.
Sometimes just getting a PC to roll a dice to see how lucky they are is fine too.
Another GM in the group takes a luck roll one step further, making the player roll a dice at the same time he does, then he judges the luck of the roll by how close the player was to his roll.
It does make sure that whatever the player rolls, they aren’t sure how lucky it really was.