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The Dungeon Master's Guide errata (direct download) added the "Combining Game Effects" section which states (emphasis mine):

Different game features can affect a target at the same time. But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap. [...]

The Essentials Kit has a further clarification on these rules in its "Names with the Same Name Don't Stack" section (page 3, emphasis mine):

[...] But when two or more effects have the same proper name, only one of them applies while the durations of the effects overlap (a duration is a time span of 1 round or more). [...]

I'm unsure whether the further clarification will change my following examples but we do know for sure that with overlapping identical effects, one instance will be what I'd call "active" (will have effects) and the other will be what I'd call "inactive" (won't have effects). That all squared away, I think my question will make more sense with examples:

  1. The Fire Elemental's Fire Form trait:

    [...] The first time it enters a creature's space on a turn, that creature takes 5 (1d10) fire damage and catches fire; until someone takes an action to douse the fire, the creature takes 5 (1d10) fire damage at the start of each of its turns.

    If a creature is under the effects of multiple instances of Fire Form, and somebody uses their action to douse the fire, are both instances removed or only one?

  2. The booming blade spell:

    [...] If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends. [...]

    If a creature is under the effects of multiple instances of booming blade, and they move, are both instances removed or only one?

  3. The hold monster spell:

    [...] At the end of each of its turns, the target can make another Wisdom saving throw. On a success, the spell ends on the target. [...]

    If a creature is under the effects of multiple instances of hold monster, and they succeed on a save, are both instances removed or only one?

Can an "inactive" effect end when its end-condition is met (letting them end simultaneously), or do these sorts of things always end one at a time? Or perhaps the answer is something in-between?


There is also the following related question:

Both answers there supports that if you are grappled by multiple creatures and you make a check to remove a grapple, you only remove one of the grapples. It's not perfectly analogous situation but it is somewhat similar.

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Good find! You've identified an ambiguity in the rules.

As I'm sure you realize, there's not a Rules As Written way to resolve this question. When it comes up, the DM will have to make a ruling at the table.

(5e is full of situations like this, so a seasoned DM should be accustomed to situations where they need to issue rulings to resolve ambiguities.)

Some DMs might rule that all of these effects stack -- if someone casts hold monster on you multiple times, you have to make a separate save for each one.

Other DMs might rule that none of the effects stack in the way you want -- meeting the end condition for one of them will end all of them.

I think a good way to resolve this is to rule: "The end condition of each instance is not a part of the effect, and the end condition is still checked even if the effect is suppressed." This means that the Fire Form trait would not stack (using an action to douse the fire would end all of the Fire Form effects), which is probably what the people designing that monster intended. The booming blade spell also would not stack. However, if a character was affected by two hold monster spells, they would save separately against each spell at the end of each of their turns.

But that's not a principled rules interpretation, it's just what seems like it would lead to outcomes that make the most sense for the three examples you listed.

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It depends on the ending conditions

The errata you listed and the Players Hand Book (p. 205) use the phrasing "the effects of one of them—the most potent one" or "the most potent effect [...] applies while their durations overlap."

It is only while the durations overlap that the other effect is suppressed. Therefore if you end one of them then the durations no longer overlap and the other effect can resume.

The cause of one effect ending might cause the other effect to end as well.

For example moving while under the effect of booming blade would also end the effect of the other because booming blade specifies that when "the target willingly moves [...] the spell ends".

This becomes less clear when the event that causes one effect to end does not necessarily cause the other to end. In the case of the Fire Elemental multiple Fire Form only cause the creature to be on fire and take 1d10 at the start of each of its turns. It is not specified, however, that the action of dousing one of the effects would be sufficient to end the other. Resolving these types of scenarios would require a DM ruling. I would suggest that a single action would douse both flames because the state of being on fire clearly doesn't stack and so extinguishing the flames would end both effects.

In the case of Hold Monster the ending requirement (aside from concentration being broken or the spell duration exceeded) is for the target to succeed on a Wisdom Saving Throw against your spell save DC. The question for the DM is therefore whether a monster succeeding on a Wisdom Saving Throw to end Hold Monster against a DC higher than your spell save DC is also, in doing so, succeeding against your spell save DC in that instant. This understanding would align with the rule stating that only the most potent effect applied in that a casting with a more difficult saving throw is functionally the more powerful instance of the spell.

I would suggest that because saving throws are instantaneous and against a particular harmful effect1 that succeeding against a higher DC automatically succeeds against any lower DCs of an identical effect at the same time. This understanding is based on the belief that attempting the same thing again in the same instant must produce identical results. A saving throw represents a creature's ability to avoid a harmful effect in an instance. This would go something like this:

  1. At Time A Jim is under Hold Person 1 with a DC of 15 and Hold Person 2 with a DC of 14 however since the two spells are identical only Hold Person 1 affects Jim

  2. At Time B Jim makes a saving throw to end Hold Person and rolls a 15 and so Hold Person 1 ends

  3. At Time B Hold Person 1 has ended and so the effect of Hold Person 2 resumes

  4. At Time B Jim's saving throw to end Hold Person is a 15 and so Hold Person 2 is ended.

This understanding would also apply to multiple grapplers except that, since it is instead a contested ability check, it is unclear which of the the two grappler's DCs would be more potent. As such each attempt to escape would require both grapplers to roll an athletics check and the grappled would need to succeed against the higher of the two.

1 "A saving throw is an instant response to a harmful effect" (DMG, p. 238)

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  • \$\begingroup\$ I think the entire clause of "If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends." entails the effect of the spell. The trigger seems to be part of the effect, so both booms would happen against the target. \$\endgroup\$ – Blake Steel May 24 at 15:25
  • \$\begingroup\$ I added a small rules-quote to my original question, I don't think it will change anything, but I realized it would probably be best to include the truly full version of the rules on overlapping effects in my question \$\endgroup\$ – Medix2 May 24 at 19:40

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