How are attacks against illusions, in particular one made by Major Image, resolved?

Question

A School of Illusion wizard (PHB p. 118) uses major image in combat to create an illusion of a monk to draw attacks from an orc. He says it takes the Dodge action and stays out of reach of the orc's sword.

How does the orc attack the illusory monk? Would it make an attack roll against the wizard's spell save DC, the Monk's AC with disadvantage, or something else?

I am looking for a RAW way to handle this for D&D 5e. I saw a related question in other editions but nothing for 5e. Lacking a RAW solution, perhaps something to suggest a RAI method would work.

Answer 1

There is no listed DC or AC for defense in the spell's description, so I think one melee attack against the illusion is enough to reveal the illusion.

From the text:

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

I don't think the illusion can appear to dodge. The spell only lists walking as an allowable moving visual, and says nothing about reacting to attacks.

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. For example, if you create an image of a 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.

Answer 2

Quick Answer: There is no RAW method for calculating the AC of an illusion. This is a conversation a DM and player should have out of game to come to an agreement but it is ultimately up to the DM.

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

Seeing as the illusory monk is dodging, the player is aware of this limit to the spell. The player's goal here is to limit physical interaction.

Illusions are incredible versatile, very open ended, and limited only by your imagination. With that open-endedness comes a lot of judgement calls as to the outcome.

If your group doesn't appreciate creativity and won't work with you, its not worth the time. It sucks the fun out of the game when you try to do something cool and get shut down. If your group just wants to roll dice you are better off throwing a fireball than planning an elaborate illusion no matter how well crafted it may be.

The player’s wizard used a spell slot, a precious limited resource at low levels. Denying any benefit at all may make them never cast that spell again and stunt the game excitement. If you on the other hand let the monk dodge for a couple rounds before being hit it will increase the storytelling value of your encounter. How you determine when that is, and possibly generate the proper level of suspense, is entirely up to the DM.

When in doubt go with the Rule of Cool. https://www.youtube.com/watch?v=fWZDuFIYkf0

Answer 3

No clear RAW answer, but several options for how to adjudicate the attack roll.

Nothing in the spell's description or general rules clearly defines what should happen in this situation. As such there are a few options that I will present, and I think you just need to see what works best for you and your players.

Things that are definitely RAW first

This "monk" cannot take the Dodge action. It can certainly look like it is dodging, but nothing in the spell description allows it to actually take actions. As such any RAI-based attack roll should not have disadvantage due to this "Dodging".

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

If the orc's sword-stroke hits the illusion, its illusory nature will be revealed.

Now RAI

Major Image is a 3rd level spell, and the highest level spell that allows you to create any generic creature as your illusion (Phantasmal Killer and Illusory Dragon are higher level, but less generic). As such, the image created is definitely intended to appear life-like - including doing things like appearing to try to evade blows in battle.

Although the image may look like a monk, it's just an illusion controlled by a Wizard. There's no reason to involve the stats of a monk here.

The options

1. Any attack hits the illusion. There is nothing in the spell description that suggests the ability to avoid attacks, so the image cannot do so.
2. AC = 4. This is the AC of a creature with Dexterity = 0 and no hardness to otherwise increase its AC. Basically the same as option 1 but including the ability of other creatures to miss. Practically speaking almost every creature has an attack bonus of at least +4, so this will only cause them to miss on critical fumbles.
3. AC = 10. This is the AC of a creature with 0 or n/a dexterity.
4. AC = 10 + something representing the "Dexterity" of the illusion. Perhaps the caster's spellcasting modifier.

I have only presented options to determine the AC of the illusion or let it get automatically hit. In my view if a creature makes an attack it should be adjudicated as an an attack roll. Not least because if the tables were turned it not being an attack roll would give your players metagame knowledge that they were fighting an illusion!

Answer 4

RAW has nothing specific for this.

However, since your Wizard uses his (readied) action to have his illusory monk dodge the orc's strikes it would be reasonable to handle it in one of the following ways:

1: Base the Illusion's AC on a relevant passive stat:

The Wiz's Passive Dex or Passive Wis/Perception (10 + Stat modifier) sound like the best stats to work with to me. Both of these could be reasoned as key factors to getting the illusion to evade the orc's strike in time.

2: Make it a contest:

Dex/Wis vs. the orc's attack. Same reasoning as above, only this time you could make it an active ordeal; the Wiz is spending their action after all.

3: Make the orc do an attack against your spell save:

Basically a spell-save using Strength for the orc.

Keep in mind these are all untested suggestions; give either option a few test-rolls with your wiz's stats and those of the orc. Then use the stats of a higher level Wizard MM or PC. After all, any illusionist you throw at them down the line will be able to do much of the same to them for whatever option you may choose.