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Mirror image (PHB, pg. 260) is a spell that has a casting time of 1 action, and a duration of 1 minute. My question is, can you cast Mirror image twice on successive turns, gaining 6 images by turn 2?

Sample Turns:

Turn 1: Mirror Image (3 images)

Turn 2: Mirror Image again (6 images, with 3 of them lasting 1 turn less)

Since Mirror Image doesn't require concentration, there should be no interference between the 2 casts in terms of concentration. I know that this could be up to DM Fiat, but I was wondering if there was a proper interpretation of the printed rules for this situation.

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Only one casting of Mirror Image will be active

The PHB says in Chapter 10 under "Combining Magical Effects" (PHB pg. 205):

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.

Therefore, only one of them will actually have their effect active. They are still both cast, though, so if one was cast later, then when the first one runs out, the second will "kick in" for as long as it has left (assuming the first was considered the "most potent").

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    \$\begingroup\$ That's somewhat similar to them stacking, though, since if the first spell is reduced to 2 images then the second spell is now more potent until it's reduced to 1 and so on. \$\endgroup\$ – Please stop being evil Nov 15 '18 at 8:52
  • \$\begingroup\$ @thedarkwanderer I was wondering that myself; I thought that was an interested enough question on its own that I've made a question for it. \$\endgroup\$ – NathanS Nov 15 '18 at 9:01
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I consider that multiple uses of the spell would overlap, and that, as pointed by the rules, the stronger current effect would be applied... So, I made a simple table considering how 2 uses of mirror images in sequential turns would work and how attacks would affect them. The colors represent from which of the spells used is the currently seen image.

1: Table of multiple mirror image uses.

Further explanation

In this case, the colors represent each use of the spell "Mirror Image", that is, each time a spell slot and an action were spent to cast the spell (in the example, the spell was cast two times, the first time on turn 1, and the second time on turn 2).

The blue color represents the images created by the first use of the spell (I called it "A"), and the green color represents the images created by the second use of the spell (I called it "B"). The column "Total visible images the enemy sees in the current turn" represents the amount of mirror images that would be visible by people looking at the caster of the spell, and the colors of the cells in this column serves to point out if the images are derived from the first use of the spell (A), or from the second use of the spell (B). To sum up, the main mechanic effects of two subsequent uses of the mirror images spell would be the following:

1st: Two turns must be spent to cast the spells.

2nd: Each group of images would have "an extra life" (meaning that each "image amount" would have to be "killed" twice in order to reduce the amount of images by 1).

The second effect is important because it represents a very interesting momentary buff for the evasion of the caster, considering the effects of having the higher number of duplicates for a longer period. Here is a copy of part of the spell description that states the odds of redirecting an attack to one of the duplicates, based on the amount of duplicates still visible:

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.

Basically, each use of the spell grants the caster an extra turn of each group of duplicates or an extra attack in the same turn at each group (the group of 3 duplicates, the group of 2 duplicates, and the group of 1 duplicate).

It is also interesting to consider that maybe 3 or more subsequent uses of the spell might also be relevant, but only until the number reaches 10 (which is the moment that the first use of the spell would naturally expire, and the following uses of the spell would not overlap at more then 10 at a time, with one spell use expiring at each subsequent turn - what would make it necessary for the caster to spend his action to cast the spell again and again, on every turn, in order to keep the 10 "lifes" for his group of 3 duplicates). The number "10" is relevant, though, because at that turn, after casting the spell 10 times, the caster could recieve 10 attacks without lowering his amount of 3 visible images (which keeps the highest odds of redirecting attacks to one of the images even if all the 10 attacks manage to "kill" one image each). Consider this as an extremely situational scenery where the caster has 10 rounds to prepare himself to rush into an extremely dangerous area with lots of potential enemies (not to mention the huge amount of spell slots/scrolls or other forms of casting this spell that would be necessary). I'm not sure about making a table for this, but I think the idea is pretty funny.

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    \$\begingroup\$ I think I understand your answer, but could you explain a bit more clearly what the color coding represents? Thanks, and Welcome to RPGSE. The tour, How to Ask and How to Answer are helpful guides in getting the most out of this site. \$\endgroup\$ – KorvinStarmast May 7 at 12:18
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    \$\begingroup\$ Thanks for the reception! I have always enjoyed the content from RPGSE, and finally found an opportunity to contribute. I have edited my answer in order to include a more detailed explanation and also an extreme example of possible use for this. Sorry if it didn't look sufficiently clear in the table (I tried not to include too much text there, to prioritize visualization a little bit). \$\endgroup\$ – SennaFF May 7 at 20:51
  • \$\begingroup\$ Thank you, it helps to understand the table. :-) \$\endgroup\$ – KorvinStarmast May 7 at 21:00

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