D&D 5E Mirror Image Math

[Ashrym]

Mirror image has a harder limit on number of attacks from which it will protect the caster. Unless the attackers really suck at hitting the AC on those images it also loses protection pretty fast.

That limit should be modelled somehow. Blur should win out long term provided solid concentration can be achieved. I haven't tried to formulate something like that since school so we'll see how long before I give up, lol.

 

[FrogReaver]

Mirror image has a harder limit on number of attacks from which it will protect the caster. Unless the attackers really suck at hitting the AC on those images it also loses protection pretty fast.

That limit should be modelled somehow. Blur should win out long term provided solid concentration can be achieved. I haven't tried to formulate something like that since school so we'll see how long before I give up, lol.

LOL. I'm finding hard to algebraically do both for blur and mirror image. It doesn't seem like the steps reduce down to a basic formula - though, it's not terrible using excel to build an algorithm to calculate though.

I find mirror image offers a lot more protection up front but decreases in effectiveness faster - whereas blur I find tends to offer less effectiveness up front (unless extremely low chances to be hit are looked at) but decreases in effectiveness slower.

Characters that dump dex and have high AC and get attacked a lot may prefer blur but I'm not convinced the difference even then is going to be great as both effects are going to trend toward taking full damage (baring con saves under +9)

 

[Ashrym]

LOL. I'm finding hard to algebraically do both for blur and mirror image. It doesn't seem like the steps reduce down to a basic formula - though, it's not terrible using excel to build an algorithm to calculate though.

I find mirror image offers a lot more protection up front but decreases in effectiveness faster - whereas blur I find tends to offer less effectiveness up front (unless extremely low chances to be hit are looked at) but decreases in effectiveness slower.

Characters that dump dex and have high AC and get attacked a lot may prefer blur but I'm not convinced the difference even then is going to be great as both effects are going to trend toward taking full damage (baring con saves under +9)

I never found the time to try, so I bolded what I find is typical IME with the caveat that blur decreasing in effectiveness more slowing is dependent on concentration ability.

 

[Dausuul]

The way I see it, blur is for eldritch knights. If you have a good Con save and a super-high AC and your primary combat function is hacking stuff to bits with a sword, blur is incredible.

If you are a primary spellcaster, however, you're much better off with mirror image. Even if blur might save you a few more hit points (haven't done the math, and I would definitely do it in a spreadsheet rather than trying to work out a formula by hand - too many variables), the fact that mirror image doesn't require concentration and blur does makes it a no-brainer. Concentration is one of a primary caster's most potent assets, and any self-defense spell should serve to protect it along with your hit points. If you have to concentrate on the defense spell, you've thrown away half its effectiveness right there.

 

[Paul Farquhar]

It matters when it can. It typically does it so rarely that it's a bullet point instead of something to factor into the formula. Get it?

It's not that rare. Especially when you consider NPC spellcasters versus a typical adventuring party, which almost always includes a rogue.

 

[Paul Farquhar]

The way I see it, blur is for eldritch knights. If you have a good Con save and a super-high AC and your primary combat function is hacking stuff to bits with a sword, blur is incredible.

Or some other way of whacking up your AC well beyond normal, such as dwarf wizard or valor bard.

 

[Dausuul]

Or some other way of whacking up your AC well beyond normal, such as dwarf wizard or valor bard.

Those are primary casters. You're still sacrificing your concentration for a defensive buff.

 

[Worrgrendel]

My wife is currently playing a level 9 High Elf Bladesinger Wizard and has both spells. She seems to get more mileage out of Mirror Image but I think that mostly has to due with using concentration on other spells such as Haste or Animate Objects. She has used Blur to great effect but she also has a very high AC and is nigh un-hitable at times short of crits (see below). She is our party tank and also has the Sentinel feat to help with stickiness. It frustrates our DM to no end.

Base AC = 10 + 3 (mage armor) + 3 (Dex) + 1 (Cloak of Protection) = 17 + 4 (Int: Bladesong; up pretty much every fight) = 21 + 2 (Haste) = 23 + 5 (Shield spell w/reaction if needed) = 28

 

[Stoutstien]

My wife is currently playing a level 9 High Elf Bladesinger Wizard and has both spells. She seems to get more mileage out of Mirror Image but I think that mostly has to due with using concentration on other spells such as Haste or Animate Objects. She has used Blur to great effect but she also has a very high AC and is nigh un-hitable at times short of crits (see below). She is our party tank and also has the Sentinel feat to help with stickiness. It frustrates our DM to no end.

Base AC = 10 + 3 (mage armor) + 3 (Dex) + 1 (Cloak of Protection) = 17 + 4 (Int: Bladesong; up pretty much every fight) = 21 + 2 (Haste) = 23 + 5 (Shield spell w/reaction if needed) = 28

I guess your DM doesn't use dispel magic alot.

This PC could go from hero to zero very quickly.

 

[Ashrym]

Those are primary casters. You're still sacrificing your concentration for a defensive buff.

Blur might still be worth it depending on circumstances.

Mirror images can take 3 hits before they become ineffective. That's the limit I mentioned earlier. If concentration can be maintained regardless of how there's going to be a tipping point based on the number of expected attacks the spell caster takes where blur becomes the obvious choice. Whether it uses up the spell caster's concentration or not becomes moot if the extra damage after mirror image drops causes the caster to drop because concentration goes with that too.

The real question would be how often the number of attacks coming at the spell caster make blur worthwhile over mirror image. I think a spell caster limited to one or the other should go for mirror image but a wizard might prep both or swap based on expected events.