I acknowledge that a terse core book means that sometimes, the mechanics might not settle into place the first time on reading. Or the second. However, with doubt come questions, and with questions comes the opportunity to put together a fuller response.
On the Discord, Guybrush asked:
Could someone please confirm whether or not someone can receive multiple step-ups or step-downs if multiple circumstances are given? e.g., d4 could be stepped up twice to a d8.
Now, as it happens, a part of this answer ties into the excellent four-part Dee Sanction Actual Play posted by Alun Rees, so stick with me!
The GM may increase or ease a Challenge’s difficulty because of environment, preparation, or enemy potency. But, broadly speaking, that step change — whether Advantage or Disadvantage — relates to one of each thing.
For example, if an Agent has fine tools and spent a week planning, that’s preparation – the GM can give one step up. It’s dark and stormy – so, the GM can give one step down from the environment. Prep and assistance – well, in that instance, maybe two steps up.
However, the GM should consider whether, if there are two steps up, is it worth rolling? Are they sufficiently prepared that it would be too easy to warrant a challenge?
The same goes for bad stuff. Lose all your die to steps down—it means a Call to Fail. But, maybe, that amount of Disadvantage should make the task impossible.
The bit that nudged me from watching the Actual Plays was this — Abilities DO NOT usually add Steps. The possession of Abilities makes things possible — which is why an Agent has a few, and generally, none will duplicate across a team.
The section of the Core Rules on page 22 — Step-Up and Step-Down — provides notes about the sources of advantages and disadvantages (as above, including prep, environment, and potency of a foe) and highlights that without an Ability, the GM can judge a task impossible.
The dice mechanic of the game already makes Agents capable — on a D6, they have a 66% chance of success.
A Challenge to fake a document for someone with Intellectuall D6 and Counterfeit does not roll a D8; it rolls a D6. Without Counterfeit, it wouldn’t be possible; or, perhaps, the GM might allow it with a Step-Down or make it a Call to Fail and leave the player to decide whether to risk success at the cost of certain peril, or accept outright failure.
That last option isn’t called out in the book, but a GM has the right to consider it. An impossible thing might be achieved at some considerable cost — generally more than just a Hit; something tangible that escalates the threat would be far preferable. In that instance, the GM offers a Call to Fail, outlines the nature of the peril and allows the player — and probably the Table — to make or deny that Call.