D&D 5E Mirror Image Math

[The Crimson Binome]

Why are you assuming that anyone would see a Mirror Image, and respond by making normal attacks against it? Isn't that playing right into their plan?

I always figured that this spell, much like any source of Disadvantage, works primarily by disincentivizing the enemy from attacking you in the first place. The ogre isn't going to risk wasting a big swing on something it probably can't hit, but the kobolds who have numbers on their side will spend their attacks because they're contributing toward the goal of making you hittable.

 

[Dausuul]

The ogre isn't going to risk wasting a big swing on something it probably can't hit, but the kobolds who have numbers on their side will spend their attacks because they're contributing toward the goal of making you hittable.

Because ogres and kobolds are known for their tactical savvy and their extensive knowledge of arcane magic?

 

[The Crimson Binome]

Because ogres and kobolds are known for their tactical savvy and their extensive knowledge of arcane magic?

If we're assuming that someone with magic is fighting ogres and kobolds, then we can assume that ogres and kobolds are known to fight people who have magic.

 

[Paul Farquhar]

Ogre smash puny wizard.

 

[Dausuul]

If we're assuming that someone with magic is fighting ogres and kobolds, then we can assume that ogres and kobolds are known to fight people who have magic.

Sure, maybe the ogre smashed a cleric once or the kobolds ambushed a sleeping wizard. That's very different from recognizing a specific spell, understanding its limitations and effects, and using the optimal counter-tactic.

 

[doctorbadwolf]

Well - not my goal but useful info.

I've calculated Blur's damage reduction for the nth attack coming at you.

Let C = Chance Concentration remains up through hit < 21 damage. X = Chance to be hit. N = Number of attacks. Then,

X - C^N * (X-X^2)

Unless you have extremely high concentration then blur actually loses value pretty quickly the more attacks come at you.

Someone else double check my work on this one!

Blur definitely gets better for someone like a Bladesinger with Warcaster. Even with a 13 con and 16 int, my Bladesinger almost never loses concentration.

Already high AC also means disadvantage attacks nearly never hit, because you need such a high die roll. In basic terms with low AC Blur is fishing for low rolls on the defensive side, while with high AC you force the enemy to fish for two higher than average rolls.

Mirror Image, OTOH, relies less on anything other than the spell itself to protect you. Not something that is easy to quantify, but certainly a benefit.

 

[The Crimson Binome]

Sure, maybe the ogre smashed a cleric once or the kobolds ambushed a sleeping wizard. That's very different from recognizing a specific spell, understanding its limitations and effects, and using the optimal counter-tactic.

If you insist on playing your monsters as clueless, then replace the example with humanoids. A barbarian (or knight) still isn't going to waste a big swing, if there's an 80% chance of missing, and there are other targets available.

You should never assume that the enemy is clueless. That's not a factor that you control, and relying on it will give you theoretical data that doesn't hold up in practice.

 

[doctorbadwolf]

Because ogres and kobolds are known for their tactical savvy and their extensive knowledge of arcane magic?

I don’t think that really requires much intelligence. The magic guy just made himself into 4 people, and it’s hard to tell what’s real. I hit slow and big, and the guy with the shield is just standing there.

It’s not advanced tactics.

 

[Paul Farquhar]

Sure, maybe the ogre smashed a cleric once or the kobolds ambushed a sleeping wizard. That's very different from recognizing a specific spell, understanding its limitations and effects, and using the optimal counter-tactic.

Mirror Image is one of the most common defensive spells used by wizards - it's even common in movies, it's one of MCU Loki's go-to spells, amongst other examples - and pretty much every wizard in Baldur's Gate CRPG casts it first. Unless it's a very low magic setting even fairly unintelligent foes are going to learn how to handle it.

 

[FrogReaver]

If you insist on playing your monsters as clueless, then replace the example with humanoids. A barbarian (or knight) still isn't going to waste a big swing, if there's an 80% chance of missing, and there are other targets available.

You should never assume that the enemy is clueless. That's not a factor that you control, and relying on it will give you theoretical data that doesn't hold up in practice.

likewise you should never assume the enemy has a clue.