Does this work similar to adding power dice to an attack roll, i.e. a hero may add one by one until he has possibly reached a desired outcome?

Or does a hero have to spend fatigue and add power dice prior to the roll on a Prolonged Action?

The rulebook leaves it somewhat open for interpretation:

Immediately after placing the prolonged action order token on your
hero, roll power dice equal to your listed trait. You may
spend fatigue to add power dice to this roll, up to a maximum
total of five power dice.

The example on the same page says:

Continuing the example listed above, Tahlia chooses to spend no fatigue, so she rolls 3 power dice.

This looks to me like you would have to decide before the roll.

Opinions here?

I thought you had to spend fatigue to add that many black dice to an attack roll before the roll. Otherwise things like aim and dodge get really complicated.

It is definitely allowed to add the dice one by one for attacks, see basic rules.

Things like Aim or Dodge vs. adding dice are clarified in the current FAQ.

I don't see why you can't add dice after the intial roll, just like any roll.

Well, look at the example above - Tahlia opts to not spend fatigue before the roll - why should she do that if she could decide that afterwards (barring she has fatigue to spend) ?

I originally came away from these rules with the impression that you had to choose to spend fatigue on prolonged orders (or not) before the initial roll, but you're correct that the rules seem to be fairly vague. I wouldn't wager one way or the other about what they intended.

Big Remy said:

Because that's not a rule for "any roll," it's a special, detailed rule that specifically applies to attack rolls. You can't spend fatigue at all when rolling for encounter markers (other than prolonged orders), traps, feats, etc. We don't have a pattern, we have one unique special case.

It's possible that they wanted to turn that into a pattern, but it's also entirely plausible that they didn't. For attacks, they go into considerable detail in multiple places to specifically point out that you can do it after the roll.

In prolonged actions, they don't even bother to specify that extra dice cost exactly 1 fatigue each (though based on the example I have no doubt that was the intent, even if they screwed up the wording in the example, too).

You could argue that they didn't go into detail because we should already know how this works from attacks. You could also argue that they didn't go into detail because prolonged orders do it the "obvious" way, and attacks needed all the detail because they didn't. I choose to believe that they didn't go into detail because they've got amazingly bad editing and it doesn't say anything at all about how this rule ought to work.

Parathion said:

Right you are. Looks like your initial question would have to be added to a new FAQ as well