[RPG] How does a Divination Wizard’s Portent work when they are not sure if/what roll the target may be making


What happens if you try to use a Portent die on a roll when the target is not in fact making a roll in the first place? For example:

  1. An enemy casts a spell on my ally (from out of sight, so I can't see exactly what spell is being cast) and I try to use Portent to give my ally a high roll on their save. But it turns out that it's not a spell that allows a save in the first place.

  2. My party is hiding from enemies, and I see enemies looking around, so I try to use Portent to give my enemies a low roll on their Perception check. But it turns out they were only passively looking so were using passive perception, and not making a check at all.

  3. I see in the distance a group of bad guys casting an evil ritual. I'm too far away to make it in time to stop it, but I do have a low Portent die so I use it on them in hopes that they are using some sort of Arcana check to do the ritual and I might be able to make them botch it (of course, they may or may not be making an actual check)

How is this handled?

  • Does the die just not get used in that case? Or does it get "wasted". Do you know if it was wasted or if it actually affected a roll?
  • How specific do you have to be as to what you are using it on in cases like this? For instance, in example (2), do I have to know exactly which round the perception check is being made (and if I guess wrong it doesn't work) or can I just say "whenever they make a Perception check to try to spot us, I use the Portent die" (assuming I can see them when they make the check) Or in (3), if they were making a check but it turned out it was a Religion check instead of an Arcana check, does that mean the Portent doesn't work because I didn't say what check they were making?

Best Answer

Mechanically, the wizard doesn't need to know what the roll is for

The School of Divination wizard's Portent feature (PHB, p. 116) says:

You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. You must choose to do so before the roll, and you can replace a roll in this way only once per turn.

The feature doesn't really explain how you know that the roll is being made (or what roll is being called for), but it's simply stated that you can use Portent to replace any such qualifying roll. As a result, you can replace any such roll that meets the requirement with one of your Portent rolls, mechanically speaking.

How to justify that in the lore is up to you and your DM. The feature does say "glimpses of the future begin to press in on your awareness", so you could justify it by saying that your wizard knew/foresaw what the roll was going to be for and what the result would be, even if you don't actually see what causes the roll in that moment. As long as you or a creature you can see makes an attack roll, saving throw, or ability check, you can replace the roll with one of your Portent rolls.

Since it's dependent on actual rolls, Portent can't be "wasted" like that

The Portent feature (or rather, your ability to replace d20 rolls using Portent) is dependent on actual rolls being made, not your or your character's knowledge of those rolls. As a result, none of those cases are issues, unless your DM house-rules otherwise (in which case it's really up to them to determine how it works, given that it's a house rule).

  1. If there's no save, you don't use (or waste) your Portent roll. If you or a creature you can see is making the save, then you can choose whether or not to use Portent to replace the roll.
  2. If the enemies don't make an active Perception check, there's no roll to replace. (Whether Portent can apply to passive checks might be its own question, but I don't think it would, as there's no d20 roll to replace in the first place.)
  3. If the enemies you can see don't make an Arcana check, there's no roll to replace with Portent.

In none of the 3 cases you described is a roll being made, so no roll is being replaced by Portent. You can't "waste" the feature by applying it to a non-roll, because it only triggers when a qualifying roll is made.