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?

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.

  • \$\begingroup\$ @SevenSidedDie: I've expanded the answer to address it. It pretty logically follows from the original answer. \$\endgroup\$ – V2Blast Jan 12 at 20:45
  • \$\begingroup\$ The interesting thing here is that it seems like Portent basically tells you when a roll is being made. This could be very useful to see what the enemies are up to. \$\endgroup\$ – Alex319 Jan 13 at 3:20
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    \$\begingroup\$ @Alex319: Well, it might tell the player, but it doesn't necessarily tell the character anything. No metagaming! :) \$\endgroup\$ – V2Blast Jan 13 at 3:21
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    \$\begingroup\$ @V2Blast unless metagaming is welcome at your table anyways (and at some it definitely is!) \$\endgroup\$ – Rubiksmoose Jan 13 at 4:51

Wait until the DM or player asks for a roll

The portent ability can be used in place of a attack roll, saving throw or ability check. You just need to wait until the DM calls for a player to make such a roll and then substitute your portent result for their roll before they actually roll their dice. Alternately if a player calls for the DM to make such a roll you can substitute your portent result in the same manner.

Keep in mind you need to see the target in order to be able to change their roll. If enemies were searching for the party and you wish to botch their search roll results then you need to be able to see them first. Chances are you can't because you are hiding from them. If you can somehow see them and they can't see you, tell the DM that if they are going to alter their results if they try rolling perception or investigation.

  • \$\begingroup\$ This doesn’t address any of the issues after “How is this handled?”, which are the point of the question asked. \$\endgroup\$ – SevenSidedDie Jan 12 at 20:38
  • \$\begingroup\$ I thought it was implied well enough. You simply can't use a portent result unless someone has called for a suitable d20 roll. They are used in response to a call for a d20 roll or a declared d20 roll. Not when you think someone is about to make a d20 roll. \$\endgroup\$ – Allan Mills Jan 12 at 23:58
  • \$\begingroup\$ Great, put that explicitly into the answer. Leaving the point of an answer implied means it’s not clear to every reader. Changing the title to “you can’t when…” or “…unless…” may be enough, but that’s up to you. \$\endgroup\$ – SevenSidedDie Jan 13 at 17:57

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