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I have a scenario that will likely never happen, but I am curious in how it would work.

First, the preliminary, Combining Magical Effects:

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect — such as the highest bonus — from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

Now the setup:

Bob the 3nd-level Generic Wizard and Doug the 3rd-level Earth Wizard face off. Bob knows Doug's favorite tactic and readies a spell. Doug casts Earth Tremor under Bob. The spell say, "You cause a tremor in the ground within range. Each creature other than you in that area must make a Dexterity saving throw."

But Bob was ready and casts Earth Tremor as a 2nd-level spell for his reaction making it more potent (more damage) in the same area.

So what happens?

Doug's casting means Doug is not targeted by the tremor. But as a reaction Bob casts a more powerful version where Bob is not targeted by the spell. So does that overpower Doug's spell? And if so, does that mean Bob no longer has to make a Dexterity save and Doug does?

There may be other spells that do this but Earth Tremor was the first I found with wording stating that regardless of the target point, the caster is not affected.

Mars Plastic
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MivaScott
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  • We've several questions regarding most potent effect for spells. Do any of these answer your question? https://rpg.stackexchange.com/questions/93074/does-the-spirit-guardians-spell-stack-with-multiple-casters; https://rpg.stackexchange.com/questions/93114/how-do-you-determine-the-most-potent-effect-for-overlapping-spells?noredirect=1&lq=1; https://rpg.stackexchange.com/questions/128318/when-a-creature-is-hit-with-more-than-one-fireball-simultaneously-do-they-take?noredirect=1&lq=1 – Pyrotechnical Jul 20 '20 at 23:22
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    You might want to use a non-instantaneous spell as an example. May I suggest charm person? – Ryan C. Thompson Jul 20 '20 at 23:33
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    I see suggestions that this may be covered by other questions/answers, but I feel this is different as a second spell is being cast to negate another. Two fireballs cast at the same person, at least one of those is going to work. But in this case, it would be like casting Fireball to keep the other Fireball from going off. – MivaScott Jul 21 '20 at 02:17
  • With Earth Tremor as the spell in example, there is nothing that differs this question from the Fireball question. If you simply read it as "are they affected by both fireballs?" rather than "do they take damage from both fireballs", the question is the same. The difference being that in fireball's case the effect is necessarily taking damage. – HellSaint Jul 21 '20 at 03:07
  • If you really want to, you can make your theoretical question a question about an Evocation Wizard casting a higher level fireball in its own party (using Sculpt Spells to make them automatically succeed) as a reaction to a lower leveled fireball in order to nullify the damage from the other one. Then I guess there's no question that the questions are a duplicate? – HellSaint Jul 21 '20 at 03:10
  • @MivaScott I specifically suggested charm person so as to preserve the negation aspect of the question. If you can override an enemy's charm spell (cast on your ally) with your own higher level one, it effectively negates it, since presumably your ally already regards you as at least a friendly acquaintance. – Ryan C. Thompson Jul 21 '20 at 16:58
  • @RyanC.Thompson, I don't see that as negating, I see that as an inconsequential side-effect. I'm still charming my ally, but (presumably) they are already friendly so being charmed doesn't matter. Whereas Earth Tremor specifically calls out, "Each creature other than you ..." so it's truly negated. It might just be my interpretation, but I don't see it as equal. Which is why I also don't see this as a dupe, but until I find a more concrete example, I'm stuck. – MivaScott Jul 21 '20 at 19:59
  • @MivaScott How about spirit guardians? – Ryan C. Thompson Jul 22 '20 at 10:56
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    @HellSaint Wouldn't that make there be no question the questions aren't duplicates? – Please stop being evil Jul 28 '20 at 22:17
  • @Pleasestopbeingevil, that's what I thought. Sounds like "Please change your question to make sure it's a duplicate" – MivaScott Jul 28 '20 at 22:25
  • I'm not telling you to change it, I'm saying it's the same question - and I'm just suggesting another way to see it how it is the same question. While the fireball question is titled as "being damaged", the actual question is "how do two instantaneous spells being cast in the same target interact?" - fireball is just a specific case of that question, and earth tremor is another. Unless you think that asking that same question once for every instantaneous spell in the game is valid and not duplicate. – HellSaint Jul 29 '20 at 16:10
  • Unless you have any reason to believe earth tremor is different in any way and for some reason the way two of them interact with the same target is different than other instantaneous spells. Then you should clarify the question. – HellSaint Jul 29 '20 at 16:13
  • @HellSaint, the big difference is, as I called out in the question, the caster, by default is immune to the spell they cast. That is not the case with Fireball. I cannot drop a Fireball at my feet and not be effected (without some other external influence). As Ryan pointed out, Spirit Guardian would be similar where the caster can choose who is and is not effected. But at this point, I wouldn't feel right changing the question as there are two answers, one specifically dealing with Earth Tremor so I don't think it would be fair. – MivaScott Jul 29 '20 at 17:45

2 Answers2

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It's an interesting question but Earth Tremor has a duration of 'Instantaneous' so, in this specific example, the two spells never overlap so Bob is targeted by the first spell and then his held spell kicks in and Doug is the target.

The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect — such as the highest bonus — from those castings applies while their durations overlap.

Page 190 of the PHB also says

If the reaction interrupts another creature’s turn, that creature can continue its turn right after the reaction

which helps reinforce the fact that two instantaneous effects do not occur at the exact same time. Thank to Thomas Markov for pointing this out.

If this scenario happened agin with spells that do have a duration longer than instantaneous then I believe your interpretation would work as you explained. But, as you pointed out, this is so situational as to be very unlikely to ever actually happen.

Steve
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You might get lucky and pull it off... and get yourself booted from the table.

First, the easy bits:

  • The spells need durations that overlap, so they must be spells with durations. That means that if your adversary is casting an instantaneous spell, this tactic will not work at all.
  • You'll need to cast it using a spell slot at least as high level as your adversary is, and for that you're having to guess.

More importantly:

  • It still produces the same effect.
  • It must be the same spell, on the same target.

Your adversary is already casting this spell on Carol. If Carol is your ally, it's probably a harmful spell. If Carol is your enemy (your adversary's ally), it's probably a beneficial spell. Either way, you don't want them to have whatever your adversary is giving, but this method of suppressing their spell gives them exactly that and more.

If Carol is your party member, you'd better have a really good explanation why you're using harmful spells on her, and don't expect "I'm keeping him from doing the same to you" to fly.

Seriously, even if you can, don't.

Stop Being Evil
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