Can Mirror Image effect be negated with a single Sacred Flame?

Question

Mirror Image description says

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.

The Sacred Flame cantrip does not require the caster to make a spell attack, its effect depends on the target's saving throw instead:

Flame-like radiance descends on a creature that you can see within range. The target must succeed on a Dexterity saving throw or take 1d8 radiant damage.

This implies Sacred Flame automatically targets the creature, revealing the original.

Is it correct, if somebody casts Sacred Flame, the "each time a creature targets you with an attack during the spell's duration" part doesn't work anymore, since everybody already knows where the original is?

Answer 1

No, sacred flame doesn't negate mirror image.

Although yes, (if your DM rules that it doesn't require accurately choosing your target) sacred flame will reveal the target briefly, how mirror image works means that information is immediately obsolete regardless, even for yourself:

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

It's not possible to keep track of the original. As soon as the sacred flame is done revealing the original by hitting it, mirror image will make sure that everyone who saw which was hit loses track of which one is real. That's what mirror image is for.

Answer 2

Although it's not an attack, the problem lies elsewhere.

Until the spell ends ... it's impossible to track which image is real.

As you say, Sacred Flame requires "a creature you can see" to make a saving throw. But which of the several creatures you can see do you choose? Clearly you have to choose a target, but it is impossible to say which the real one is.

The DM might use the same mechanic as with an attack to resolve this, or is free to use another way to determine if you correctly guess the real image.

Answer 3

I'm pretty sure Sacred Flame works regardless of the existence of the illusory duplicates (since it doesn't require an attack roll), but I also don't think it renders the duplicates useless. 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." I would say that subsequent to the Sacred Flame those duplicates still exist (because nothing has removed them), and it would still be impossible to tell which is which (because the spell says it is, and because you're in the thick of combat, so it's logically difficult to keep track of which duplicate is which).

Answer 4

I'm going to say, No, it does not negate the Mirror Image -- however, it does do damage if the target fails its save. It does not however mark an Image as being an Image or allow for damage avoidance, since, the targeting requirement is "any creature you can see within range".

I'm going to say that if you can see the Mirror Images, you can see the Original -- thus, it does exactly what the spell says it does and causes damage, upon a failed save.

I'd argue it's exactly similar to the interaction of Mirror Image and Magic Missile (asked in a previous question) -- that the target is always affected.

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I'll expand my answer to still say No. Because it's not targeting or causing damage to an Image, rather to the Original -- as, I remember Mirror Image, hitting/causing damage to an Image reveals it's illusionary nature -- however, in this case it isn't damaging Images. (I forget if 5e does that, but, assuming it doesn't it still wouldn't matter)

My take would be you couldn't tell which was the Original, because, every copy would instantly show the same effects. There'd be no, instant 'they're the real person' moment. It'd still be down to the "you're unable to distinguish the difference".

Answer 5

No one knows where the original is because Mirror Image clearly states that it is impossible to track which is which. It is explained that the illusions move in such a way that no one can keep track of any.

shifting position so it's impossible to track which image is real (Mirror Image, PHB pg.260)

Which probably means that they "switch" place every once in a while (without requiring the user to do anything special).

Ask your DM whether there is an opening created by painting a target on the original when Sacred Flame is used before the illusions move and hide him again. There could have an argument for allowing an ally that readied an action to attack just after but as always you should respect his decision.