When a roll is rerolled, how does it interact with other roll-manipulation features (like the Lucky feat)?

Question

A 14th level Monk has a Diamond Soul.

Whenever you make a saving throw and fail, you can spend 1 ki point to reroll it and take the second result.

A 9th level Fighter has Indomitable.

You can reroll a saving throw that you fail. If you do so, you must use the new roll.

The Lucky feat states that:

You have 3 luck points. Whenever you make an attack roll, an ability check, or a saving throw, you can spend one luck point to roll an additional d20. You can choose to spend one of your luck points after you roll the die, but before the outcome is determined.

So, if a Fighter or a Monk re-rolls their Saving Throw, does that mean they cannot then use Lucky? Or is the wording just meant to say you don't pick one of the 2 values, but instead just the new one?

As an example:

Fighter rolls a WIS Throw, rolls 1 and DM informs him he failed the save. Fighter uses Indomitable and rerolls, getting a 10. Before the DM tells him whether he succeeded or not, can the Fighter decide to roll an additional Luck die, or must he take that 2nd Indomitable roll?

Answer 1

You can spend Luck on the first roll or the re-roll, or both.

Read the rules carefully. You "spend one of your luck points after you roll the die, but before the outcome is determined". So you use Luck before you have failed the saving throw.

Diamond Soul lets you spend a ki point to reroll whenever you make a saving throw and fail. That's after the outcome is determined. The same goes for Indomitable.

So if you use a Luck point, you get to roll one additional die to determine the outcome of the roll. If you then don't succeed on the saving throw, you've "made a saving throw and failed". So then you can use Diamond Soul or Indomitable to re-roll. If you want, you can use Luck on the re-roll too, before the outcome of that is determined.

Note that if you roll a Lucky die, you can choose to ignore it. It's not a "re-roll" so you don't have to keep it.

Example: Fighter rolls a Wisdom Saving Throw, rolls 1, and decides not to use Luck because they have Indomitable. The DM informs them the save failed. The Fighter uses Indomitable and re-rolls, getting a 10. Before the DM tells them whether they succeeded or not, the Fighter can decide to roll an additional Luck die.

Answer 2

You should be able to use Lucky to manipulate any roll as long as the end result is unknown to you.

...within the feature's limits.

A 9th level Fighter has Indomitable:

You can reroll a saving throw that you fail. If you do so, you must use the new roll.

With my emphasis above, a new roll means it's a separate roll from the failed one so the phases of rolling should repeat. That means you should be able to use Lucky since the result of this new roll is undetermined again.

The wording on the Diamond Soul is different but I can see the meaning going both ways.

• You must use the second result so you can't manipulate the roll anymore.

• You must use the second result but between rerolling and determining said result you may use Lucky to manipulate it.

  Because Lucky manipulates a roll, not the result, should be the second point.)

Seems a bit based on the DM's understanding of the exact words on these features.

My understanding: Whether it is before or after using other features, as long as the end result is unknown, you can choose to spend a Lucky point to roll an additional die and choose which die to use for that roll.

My opinion: Using Lucky after using one of those features actually diminishes its power as you could've had the effect of Lucky all along. It's just saving the Lucky point until the last moment of desperation in case you can succeed without it. That sounds to me like actual last second luck which makes it more realistically awesome. That said I don't see why it wouldn't be allowed.