How do the Faerie Fire and Mirror Image spells interact?

Question

During a discussion on how mirror image interacts with area of effect spells, and particularly with magic missile, the question arose about how faerie fire interacts with mirror image. This is related to the general question of how mirror image interacts with spells that don't have an attack roll but is more specific.

The faerie fire spell description states:

Each object in a 20-foot cube within range is outlined in blue, green, or violet light (your choice). Any creature in the area when the spell is cast is also outlined in light if it fails a Dexterity saving throw. For the duration, objects and affected creatures shed dim light in a 10-foot radius.

Any attack roll against an affected creature or object has advantage if the attacker can see it, and the affected creature or object can't benefit from being invisible.

The description of mirror image says:

Three illusory duplicates of yourself appear in your space. Until the spell ends, the duplicates move with you and mimic your actions, shifting position so it's impossible to track which image is real. You can use your action to dismiss the illusory duplicates.

Each time a creature targets you with an attack during the spell's duration, roll a d20 to determine whether the attack instead targets one of your duplicates.

If you have three duplicates, you must roll a 6 or higher to change the attack's target to a duplicate. With two duplicates, you must roll an 8 or higher. With one duplicate, you must roll an 11 or higher.

A duplicate's AC equals 10 + your Dexterity modifier. If an attack hits a duplicate, the duplicate is destroyed. A duplicate can be destroyed only by an attack that hits it. It ignores all other damage and effects. The spell ends when all three duplicates are destroyed.

Does faerie fire only light up the creature who cast mirror image, or do all of the illusory duplicates also get outlined/lit up by faerie fire?

Our guess was that faerie fire lights up all of the images, but since faerie fire is working like an AoE spell, and AoE spells aren't fooled by the images (fireball, etc), perhaps we misunderstood how these two spells interact.

Answer 1

I would rule that the original and the duplicates all have the effect of faerie fire visible. Faerie fire would outline all the duplicates and give advantage on attack rolls regardless. However while the spell does say

A duplicate can be destroyed only by an attack that hits it. It ignores all other damage and effects.

Mirror Image also says

Until the spell ends, the duplicates move with you and mimic your actions, shifting position so it's impossible to track which image is real.

I think that the duplicates would not be affected by faerie fire directly BUT seeing as the original is affected, they would alter their appearance to match that of the original thus conferring advantage to attacks made on them as the advantage is a result of faerie fire's outline making it easy to see the affected creature. (Otherwise why would the spell have to specify "if the attacker can see it"?)

Answer 2

Only the creature gets hit with faerie fire, but all the images light up

Mirror image says:

Until the spell ends, the duplicates move with you and mimic your actions, shifting position so it’s impossible to track which image is real.

Note that the spell says that its main effect is to make it impossible to tell the original from the images. This could not be true if the images did not change appearance with the real creature.

If the creature takes off their shirt, the images take off shirt. If a creature gets a vat of paint dumped on them, the images also become painted. If the creature gets hit with a spell that changes their appearance, the images also change to match. If the spell would not do this then simply hitting a creature enough to rip a shirt or put a blood spot on them would be enough to negate the entire spell's effect.

So, the creature is the only one to be targeted by the faerie fire, but, because the effects of mirror image specifically make it so that the images are impossible to tell apart from the real thing, the images also appear to be affected as well.

Mechanically, this illumation will have no effect on anything about the duplicates except their appearance because:

A duplicate can be destroyed only by an attack that hits it. It ignores all other damage and effects.

In other words, creatures only get advantage on attacks against the real creature; the images disregard faerie fire completely (no advantage against them).

Rules as intended agrees

Jeremy Crawford, official rules designer for 5e, addresses a related question here:

Q: if you have mirror images out and then cast invisibility on yourself, do the mirror images also become invisible?

Jeremy Crawford: Mirror image creates illusory duplicates of you that imitate your appearance. If your appearance goes away—you become invisible, for example—then the duplicates imitate that too.

Since JC rules that even magical invisibility will be imitated by the duplicates, it seems obvious that faerie fire would fit that ruling perfectly as well.

tl;dr The creature is the only one affected by faerie fire, but all the images do still mimic the appearance of being under the effects of it.

Answer 3

All images are illuminated, but there is no benefit.

Since these spells cause two distinct and specific effects, we can't rely on the rule of thumb that specific beats general. Instead, we need to find a ruling that harmonizes both specific effects. I believe there is only one sensible and consistent ruling.

Note the following from the text of the mirror image spell (emphasis mine):

Three illusory duplicates of yourself appear in your space. Until the spell ends, the duplicates move with you and mimic your actions, shifting position so it's impossible to track which image is real.

The only way for faerie fire to affect its target in such a way that it's still impossible to track which image is real is for all the target's mirrored images to appear to be illuminated. Any other ruling would make it literally possible to tell the images apart, which mirror image expressly forbids.

Then note the following from the text of the fairie fire spell (emphasis mine):

Any attack roll against an affected creature or object has advantage...

Despite the appearance that the mirror images are illuminated, there is no mechanical impact, because the images are not creatures or objects (as they are not indicated to be either).

To summarize: the target and all images appear illuminated, but there is no practical mechanical benefit except against the target creature itself.

Answer 4

I agree that the figures light up, even if they are not affected by the spell itself.

But I would also argue that you get the advantage against them.

The main argument against is that the images are not affected by the spell, but since the faerie fire advantage is a purely visual effect that makes it easier to hit (which is why you get no advantage if you can't see it) I would say they would copy that any way same as with invisibility. You either include all the effects because of vision (including the advantage) or none (in which case you can see which is real). If all the weak points are highlighted on you, they are also highlighted on the images, thus the images would also be easier to hit.

If those are not shown, then it would be easy to distinguish the real thing since there are visual differences which the mirror image should not allow.

Answer 5

By RAW, only you are illuminated by Faerie Fire, but Mirror Image still works

Each object in a 20-foot cube within range is outlined in blue, green, or violet light (your choice). Any creature in the area when the spell is cast is also outlined in light if it fails a Dexterity saving throw.

The spell is clear: Only objects and creatures are outlined. Since the copies made by Mirror Image aren't objects or creatures (they are a spell effect), they are not illuminated.

Mirror Image does copy your appearance, however I would argue that Faerie Fire does not change your appearance, as a spell such as Invisibility does. Rather it creates an effect that just happens to surround you. Thus, there is no reason to think that the other targets would be surrounded by Faerie Fire.

Note that, by RAW, this doesn't actually interact with Mirror Image at all. Spells do what they say, and Mirror Image doesn't provide any clause for what to do when the real target is known. So, you would still need to make a roll to see if your target is real or fake.

Going further, since Mirror Image changes your attack roll, you would only get advantage if you managed to target the real target. If you target an illusion, it is not affected by Faerie Fire, and so you don't get to attack with advantage.

To summarize: Faerie Fire only outlines the original target. To attack, the attacker still need to roll to determine their target. They get advantage only if they are lucky enough to target the real target.

Answer 6

Faerie fire is Faerie "Fire". An illusionary image isn't capable of catching fire, even if the flames are harmless. To a Dungeon Master, I'd ask what happens to the caster of Mirror Image if his robes were to catch fire. Would the illusionary images mirror the flame or mirror the damage on the caster's skin? Or what if the caster runs through knee-high water? Do the illusions also kick up water? What about the snow? Do the illusions leave tracks in the snow? My understanding is that the answer is no, they don't kick up water and they don't leave tracks in the snow. So...the 2nd level spell Mirror Image isn't foolproof on a practical, real-world (kinda), level.

Answer 7

I read it as the mirror images also being affected because, by RAW, spells do what they say they do, and only outlining the real person would either:

1. Only outline the benefactor of Mirror Image, giving advantage to hit him, but with the benefits of Mirror Image staying, which is silly (I can tell which one is the real guy, but I hit his duplicate instead. Oops.), or

2. Faerie fire becomes a hard counter to Mirror Image. Seeing as the spell only calls out Invisibility, I don't think that it's RAW or RAI for Mirror Image to become useless when someone blasts them with Faerie Fire.

Personally, I would rule it as the Faerie Fire only affecting the target, but the fire also being mirrored, making it appear to target the duplicates as well.