Can a character use a luck point to affect a roll that was replaced by Portent?

Question

When a divination wizard character uses their Portent ability:

Starting at 2nd level when you choose this school, glimpses of the future begin to press in on your awareness. When you finish a long rest, roll two d20s and record the numbers rolled. 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.

... to replace a roll, can a player with the Lucky Feat:

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. You choose which of the d20s is used for the attack roll, ability check, or saving throw.

You can also spend one luck point when an attack roll is made against you. Roll a d20, and then choose whether the attack uses the attackers roll or yours.

If more than one creature spends a luck point to influence the outcome of a roll, the points cancel each other out; no additional dice are rolled.

... use the Luck Roll to replace the result? Or does the Portent trump all rolls and simply give you the final outcome?

This question spun off from discussion on this question.

Some relevant points:

Portent trumps Advantage/Disasgvantage.

Mike Mearls tends to believe that luck can triumph in some cases, but admits this is his opinion, and further seems to conflate the question with Halfling Luck.

I would suggest reading the linked discussion before formulating an answer. There's some good thought there.

Answer 1

Portent overrides Lucky

Lucky allows you to choose which of two dice to use as the roll.

Whenever you make an attack roll, an ability check, or a saving throw... You choose which of the d20s is used for the attack roll, ability check, or saving throw.

Portent replaces the roll wholesale.

You can replace any attack roll, saving throw, or ability check

So lucky allows you to choose which toss of the die to use for your roll. Unbenownst to the lucky roller, portent replaces the roll entirely regardless of which die toss was selected as the roll.

Answer 2

I think that RAW is unclear about it, so I'll present my reading on it, from a few different points of view. By the end, I present my point on a more flavorish style, rather than mechanical/RAW.

RAW

Portent states

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.

Lucky

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. You choose which of the d20s is used for the attack roll, ability check, or saving throw.

I will, without loss of generality, assume we are talking about attack rolls (so I don't need to say "attack roll, saving throw or ability check" and instead I can just say "attack roll", I'm THAT lazy).

One way to read it is that the "attack roll" is replaced by a "foretelling roll". As Lucky doesn't state "when you make a foretelling roll", Lucky can't be applied after Portent. This reading has further implications on many interactions that are probably not intended, mainly with any feature written as "When you make an attack roll". This is focused on the bold emphasis. It is, however, an interpretation of what's written.

Other way to read it, based on the italic emphasis, is that the Portent replaces the roll and actually you don't roll any die when making the attack roll, so, again, the trigger after you roll the die doesn't happen.

There is also the reading presented by Grosscol, in which Lucky only allows you to roll an additional dice and then choose which one is the roll, while Portent replaces the roll as a whole. This is consistent with the Adv/Disadv ruling you mention. In this reading, the process would be resolved similar to the Adv/Disadv:

1. The wizard declares he is using Portent before the roll. For example, he declares an attack and uses his 18 roll.
2. The wizard rolls the attack roll die. Following the example, say he gets a 19. The enemy uses the Lucky feat, forcing the Wizard to roll an additional attack roll die, in which he gets a 2.
3. The Lucky feat resolves. The enemy decides the result is a roll of 2.
4. The 2 is replaced by the 18.

Addressing the Portent then Lucky scenario mentioned by NautArch

Maybe this is a result from me playing too much Yu-Gi-Oh!, but I read a trigger "Whenever X, Y" as "Y has to happen immediately after X". This means the following order

1. The wizard declares he is using Portent before the roll. For example, he declares an attack and uses his 18 roll.
2. The wizard rolls the attack roll die. Following the example, say he gets a 2.
3. Portent resolves. The 2 is replaced by the 18.
4. Ene Enemy chooses to use Lucky. The Wizard rolls an 8.
5. The Lucky feat resolves. The enemy decides the result is the roll of 8.

can't be done because the "When an attack roll is made against you" is not the "last thing" that has happened - the portent resolving is. I.e., Lucky had to be activated right after step 2, and step 3 happening makes it miss the timing for its trigger.

So, to sum it up, my reading of RAW is Portent overrides Lucky. My reasoning to disagree with NautArch is simply on how I read the "When X..." trigger. If you read it as "any time after the roll, but before the outcome" (rather than "immediately after the roll"), then the order presented in this last subsection is valid.

If you want to let both orders to be valid

You can rule Portent and Lucky as simultaneous effects (both happen "When you make an attack roll...", even if the meta instant (before/after rolling a dice) is not the same, the "in-game" moment they happen is essentially the same) and rule it as XGE suggests

Most effects in the game happen in succession, following an order set by the rules or the DM. In rare cases, effects can happen at the same time, especially at the start or end of a creature’s turn. If two or more things happen at the same time on a character or monster’s turn, the person at the game table — whether player or DM — who controls that creature decides the order in which those things happen. For example, if two effects occur at the end of a player character’s turn, the player decides which of the two effects happens first.

This might be a little stretching, but I think it has its merits.

Rules as Fun/Flavor

Portent is basically "The Wizard knows what is going to happen", something like knowing destiny.

Lucky is being incredibly... lucky.

Is being lucky enough to override destiny?

I honestly think it isn't. My reasoning is simple: while the luck might fail (even if you roll an additional d20, you can still get a worse result and have to stick with the initial one), destiny is always right.

But I don't see any reason to not rule it as "He is so lucky that he defies destiny sometimes, making even the best fortunetellers drop their jaws".

Answer 3

Both apply

If a person uses portent:

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.

So say a character declares an attack, the wizard doesn't want to be hit so he applies his portent (low roll) to the roll before the character rolls it. That is in essence replacing the characters roll with the roll the wizard got with his portent die

The character can then use his lucky feat to:

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. You choose which of the d20s is used for the attack roll, ability check, or saving throw.

The character then rolls another d20 and chooses to either take that roll or the portent roll he was given.

Answer 4

Jeremy Crawford unofficially states on Twitter that the Portent feature overrides advantage/disadvantage.

To expand on this logic, the following is the process for rolling any skill check, attack roll, or saving throw where the lucky feat and the Portent feature are both used:

1. Wizard declares their use of their Portent feature.

2. Roll 1d20

3. if you have advantage/disadvantage, roll a second 1d20

4. You trigger your Lucky feat (after the die roll, but before the result is declared). Roll an additional d20.

5. Select the die you would like to use. This is the result of the roll.

6. Replace the result of this roll with one of your pre-rolled Portent dice.

7. Add modifiers as relevant and inform the DM of the result.

Due to this order, the Lucky feat never has any impact on the result of the roll when the Portent ability is also used. Because of this, many DMs will just chose not to roll, since it is irreverent.

(Even if you had disadvantage, due to the wording of the Lucky feat, you get to pick any of the 3 rolls at step 5.)

Answer 5

As an Alternative: They Cancel Out

Before anyone jumps to conclusion too quickly, I know that (by the book) Portent trumps Lucky.

However, that doesn't have to be the case as D&D tends to have loopholes and broken interactions when you look close enough (i.e. Simulacrum + Wish = no-stress wish). As such, we can conclude that D&D rules aren't all-encompassing. If you are looking for a game that has balance, you might want to reinterpret the Lucky vs Portent (if you are not satisfied with it) to the same way Lucky vs Lucky might work:

If more than one creature spends a luck point to influence the outcome of a roll, the points cancel each other out; no additional dice are rolled.

To me, they are both similar where as Lucky vs Portent is akin to Order/Destiny vs. Chaos/Change, a Lucky vs. Lucky is akin to Chaos vs. Chaos (all of them are very close concepts to each other), but that is all just my suggestion to preventing conflict.