Does an attack against an illusory duplicate from the Mirror Image spell trigger the Sentinel feat?

Question

If I'm playing a Rogue with the mirror image spell and possess the Sentinel feat, do I get an opportunity attack if an enemy attacks me in melee but hits a mirror image instead?

Would this trigger Sneak Attack?

Answer 1

Mirror Image states (p. 260 PHB)

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.

So:

1. a creature intends to target you,
2. you roll to determine if the creature in fact targets you OR one of your duplicates.

Sentinel states (p. 170 PHB)

When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn’t have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.

So:

1. if the creature in fact targets one of your duplicates then it hasn't targeted you; it does not need to hit the image, just target it
2. the image is an illusion so it does not have this feat

then you can use your reaction to make a melee weapon attack against the attacking creature. This is not an opportunity attack.

Sneak Attack states (p. 95 PHB)

Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.

You don’t need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn’t incapacitated, and you don’t have disadvantage on the attack roll.

So,

1. if you haven't used sneak attack this turn
2. you have advantage (or an enemy of the target within 5 feet and no disadvantage; you could try to get your DM to agree that any images you have count - good luck with that)
3. you have a finesse melee weapon available

then this could be a Sneak Attack.

TL;DR

1. You can make an attack - this is not an Opportunity Attack.
2. If you meet the requirements, this may be a Sneak Attack.

Answer 2

Yes, it does trigger the feat (if the attacker's within 5 feet of you)

Rules designer Jeremy Crawford unofficially addresses this question in a tweet from October 2018:

Todd Kenreck: When using mirror image. Does an attacker who targets a mirror image instead of you provoke an attack from the Sentinel feat?

Jeremy Crawford: Yes.

This is supported by the descriptions of the spell and feat.

The mirror image spell description states:

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.

The spell has the potential to change the target of the attack from you to an illusory duplicate that shares your space.

The third benefit of the Sentinel feat (PHB, p. 170) says:

When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn't have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.

The Sentinel feat's third benefit triggers when a creature within 5 feet of you attacks another "target" besides you.

Mirror image definitely has the potential to change the target of the attack from you to an illusory duplicate, meaning that the attack is being made against a target other than you. Your illusory duplicates are only illusions, nothing more - nothing in the spell description says they copy anything but your appearance, so the illusory duplicate doesn't have the Sentinel feat (it's not even a creature). As a result, the prerequisites for the Sentinel feat's third benefit are met as long as the enemy is within 5 feet of you, and you can use your reaction to attack the enemy in response.

(Your reaction occurs only after its triggering attack, as usual, so the illusory duplicate may or may not be destroyed depending on whether the enemy's attack hits the duplicate it targets.)

No, it doesn't automatically trigger Sneak Attack

The Sneak Attack feature says:

Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.

You don’t need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn’t incapacitated, and you don’t have disadvantage on the attack roll.

Even if you use a finesse or ranged weapon to make your reaction attack from Sentinel, nothing about the given example implies that the prerequisites for Sneak Attack are met.

You can use Sneak Attack outside your turn (it's once per turn, not once per round); that's not the issue. However, unless you have advantage from something else or you have some subclass feature that gives you another way to qualify for Sneak Attack, you haven't met the requirement I've bolded, which is worded differently from Sentinel.

Sentinel only requires an attack by a creature within 5 feet of you against a "target" without the Sentinel feat. However, (regular) Sneak Attack requires something different, if you don't have advantage: "another enemy of the target" of your attack needs to be within 5 feet of the target you're attacking. An illusory duplicate created by mirror image can't actually do anything besides mimic your movements; it's just an illusion that looks like you. As such, it can't reasonably be described as an "enemy" of your target, so that is not enough to trigger Sneak Attack on its own.

This aspect of the issue is also addressed in this question: Does Mirror Image enable Sneak Attack?

Answer 3

The text can be read either way, and it's up to the DM to decide.

There are two ways of looking at the combined powers, and it's going to depend on how you read "targets". Is it merely describing a verb which indicates what/who takes damage, or is it a verb which is describing the new state of the noun of who the target is?

If you read "targets" mostly as a verb, then: No, the two powers do not combine.

When you have cast mirror image on yourself, the creature attacking makes an attack against you. That attack fails, and instead goes to your illusory duplicate. However, they made the attack against you. So you can't use the sentinel feat.

The Sentinel feat does not say "When a creature adjacent to you fails to target you with an attack" - which is what is actually happening in this situation. They made an attack against you, but failed to target you.

However, others may read it that since the illusory duplicate is - strictly speaking - not you, and the target has shifted to something which the enemy thinks is you, but is not actually you, then the Sentinel feat applies.

Looking over the internet, the interpretation that both powers combine to work together is the more popular ruling, namely because it costs both a feat and a spell which normally would not be the best choice for a rogue. It also seems to depend on whether people are concerned about the intent of the feat as being one which forces enemies to attack you and not another team member, or if the intent is one which allows you to get free attacks if you have the slightest opening. Another concern is what this combination of attacks looks like; one of the "mirror images" is able to act differently than all the other illusory duplicates, seemingly breaking the illusion.

However, most agree that even if the two spells work together, the illusory duplicate would most likely not count as an adjacent ally, since all copies occupy the same space, and strictly speaking, the duplicate is an illusion, and not an ally.

Answer 4

No, it does not

Mirror Images are a copy of you.
You have the Sentinel feat; therefore, they also have the Sentinel feat.

The Sentinel feat reads:

When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn't have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.

(emphasis mine)

This means there is no attack because your images have the Sentinel feat.