For reference, the major image spell description states:

You create the image of an object, a creature, or some other visible
phenomenon (1) that is no larger than a 20-foot cube. The image appears
at a spot that you can see within range and lasts for the duration. It
seems completely real, including sounds, smells, and temperature
appropriate to the thing depicted. You can’t create sufficient heat or
cold to cause damage, a sound loud enough to deal thunder damage or
deafen a creature, or a smell that might sicken a creature (like a
troglodyte’s stench). (2)

As long as you are within range of the illusion, you can use your
action to cause the image to move to any other spot within range. As
the image changes location, you can alter its appearance so that its
movements appear natural for the image. (3)

For example, if you create an image of a (4) creature and move it, you
can alter the image so that it appears to be walking. Similarly, you can
cause the illusion to make different sounds at different times, even
making it carry on a conversation, for example.

(PHB p. 258, emphasis mine)

What I'd like to do:

Cast the spell in such a way that I stand among a 20ft x 20ft square filled with illusions that are exact images of me, and move in tandem with them in an attempt to have an opponent strike an incorrect copy of me, a la (small Infinity War spoiler)

Dr. Strange when he faces down Thanos.

Points to consider regarding my annotations:

• (1) Does the purview of "some other visible phenomenon" cover me
  here? I'm not trying to "break" the spell necessarily; what I'm
  trying to create is a visible phenomenon.




• (2) These seem to be the only explicit limiting factors, though I
  acknowledge the intent behind them seems to only be to limit certain
  advantageous affects which the spell cannot grant.




• (3) Because it's a single casting and not multiple uses of the spell,
  would the images be required to move synchronously?




• (4) The "a" here. Is it limiting? Does it only apply to the example
  the spell offers and thus, not to other scenarios (mine included)
  necessarily?

Other points raised:

• I have considered that, if disbelieved, the spell would cause ALL
  copies of me to be found-out and made transparent, as it is a single
  spell. I still can see tactical advantages to be gained in using the
  spell in this way regardless.




• I acknowledge this could be a situation where the answer is "It is
  up to your DM".




• I acknowledge "spells only do what they say they do"; I am having
  trouble understanding what this spell says it does.




• Mirror image exists; for me, it is not a desirable replacement because if major image could do this, then it offers a mirror image-like ability and also the rest of what major image can do, and is therefore a stronger spell.




• I would prefer answers based on RAW.

Major image only lets you create one image of yourself

an object, a creature, or some other visible phenomenon

Note the singular there. Only one illusion of one creature can be created by the spell.

Does the purview of "some other visible phenomenon" cover me here? I'm not trying to "break" the spell necessarily; what I'm trying to create is a visible phenomenon.

No, it doesn't. Note that it says "other" visible phenomenon. That means visible phenomenon other than the two categories (object and creature) previously talked about. It doesn't mean "other phenomena" in the sense that you can ignore the limitations previously mentioned in the spell. The phrase is only there to allow you to create non-creature, non-object illusions (eg a rainbow or fog).

If major image was designed to allow this they would not have put the words "a creature" in the first line of the spell. Instead they would have said "objects or creatures or other phenomena". But they didn't and thus the RAW of this spell simply does not allow it to be used in the way that you want it to.

There is already a spell that does exactly what you want to do: mirror image

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.

This is exactly what you are trying to do with major image and since it won't work with major image you should just use it instead. The spell is literally tailor-made to achieve the effect you wanted. Mirror image is even a lower spell level than major image so you can get the same effect by using less resources.

Major image and mirror image are different spells that are designed to do very different things

Mirror image is a one trick pony; all it can do is create illusory duplicates of yourself to aid you in battle. Useful if you want that one particular thing, but not so useful otherwise. Major image is a very versatile spell that can be used for all manner of strategies both in battle and out. It can create illusory hiding places. It can create illusions of threats to scare off enemies. You can create illusion of treasure to set up a trap. You can create a single illusion of yourself to talk to the enemy leader and avoid exposing yourself to danger.

They are simply two spells with two different effects and ways they were designed to be used.

Regardless, the wording of major image explicitly shuts down what you are trying to use it for, it simply was not designed to duplicate the effects of mirror image.

^{Even if major image could duplicate mirror image's effects (again, it absolutely cannot), it would be strictly worse than mirror image in just about every way in doing the one thing mirror image was designed to do.}

^{1. Major image uses a higher spell slot}

^{2. Major image requires concentration (mirror image does not)}

^{3. Major image requires you to use your action to make the images move with you (mirror image does it for free)}

^{4. Major image disappears upon simple physical examination or an ability check. Mirror image requires each image to be hit with an attack.}

^{5. Major image’s illusions disappear at the same time. Mirror image only has the hit one disappear.}

^{There is simply no conceivable way that using major image the way you imagine it would be better than using mirror image instead.}

Let's try to interpret RAW in the absolute most beneficial way possible for you here.

You create the image of an object, a creature, or some other visible phenomenon (1) that is no larger than a 20-foot cube.

Some other visible phenomenon is not strictly prohibited from being multiple copies of you.

As long as you are within range of the illusion, you can use your action to cause the image to move to any other spot within range. As the image changes location, you can alter its appearance so that its movements appear natural for the image.

But then here we see a problem for your use case: You must use your action to make the image move around.

But let's say you do that, and you're fine with ditching your action every turn.

In that case, congratulations! You've invented a worse version of Sanctuary, that is two levels higher. If a target chooses to attack you, they might hit a duplicate instead. We don't know whether that involves a saving throw or a %chance though - that would have to be ruled by the DM.

But then if they don't hit you, they immediately see through all of the duplicates:

Physical interaction with the image reveals it to be an illusion, because things pass through it.

So, with a DM who's on board, you might be able to use Major Image to duplicate the effects of Sanctuary for a single attack.

The same minor Infinity War spoiler follows:

Then again, that's about as effective as Doctor Strange was, so maybe that's what you're after?

You can do this, but it won't help much.

"An object, a creature, or some other visible phenomenon" means any visible phenomenon.

You could make all of them move using your action, though it's unclear if you could walk in the middle of the group and have them move with you. (This depends on how your table handles the timing of turns. I'd allow it, on the basis that you can animate an image to "walk", and therefore it moves continuously, not all at once.)

However, as soon as your foe sees a hundred exact duplicates of you moving in tandem, they'll know it's an illusion because there aren't really a hundred of you. They will then be able to see through the illusion.