Author Topic: Mirror Image & Miss Chance  (Read 2751 times)

Offline sirpercival

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Mirror Image & Miss Chance
« on: March 31, 2013, 08:43:37 AM »
OK, so here goes.

1. The Child of Shadow stance (like other effects) grants you a 20% miss chance.
--> You have an 80% chance of being hit.
2. The Mirror Image spell (let's say you have max images) grants you essentially an 87.5% miss chance.
--> You have a 1-in-8 chance of being hit, and a 7-in-8 chance of an image being destroyed instead.

When you combine these, which order do you apply things in?  The FAQ says that the images gain the benefit of the miss chance (paraphrasing), so it seems that the miss chance should be applied second.

Thus, we have four possible outcomes (assuming an attack roll high enough to hit both you and the images):
1. Attacker targets an image (87.5%) and misses due to miss chance (20%) = 17.5%
2. Attacker targets an image (87.5%) and hits, destroying the image (80%) = 70%
3. Attacker targets you (12.5%) and misses due to miss chance (20%) = 2.5%
4. Attacker targets you (12.5%) and hits, dealing damage to you (80%) = 10%

Did I screw up anywhere?
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Offline Agnostic Paladin

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Re: Mirror Image & Miss Chance
« Reply #1 on: March 31, 2013, 11:32:09 AM »
Wouldn't be a series of three rolls? A normal to hit roll vs. your AC, then a 20% miss chance, then a random roll to see if he hit you or an image. If he doesn't hit your AC, the other rolls become irrelevant, and if he misses on the second roll, then the roll to see if he hit an image or not becomes irrelevant.

Offline sirpercival

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Re: Mirror Image & Miss Chance
« Reply #2 on: March 31, 2013, 11:42:47 AM »
Wouldn't be a series of three rolls? A normal to hit roll vs. your AC, then a 20% miss chance, then a random roll to see if he hit you or an image. If he doesn't hit your AC, the other rolls become irrelevant, and if he misses on the second roll, then the roll to see if he hit an image or not becomes irrelevant.
That would make sense, except that it definitely doesn't work that way.

Quote from: d20SRD
Enemies attempting to attack you or cast spells at you must select from among indistinguishable targets. Generally, roll randomly to see whether the selected target is real or a figment. Any successful attack against an image destroys it. An image’s AC is 10 + your size modifier + your Dex modifier.

Not only does the initial language suggest that the selection happens first, but the figments have their own AC.  That seems to me to imply that the order is: select target -> roll to hit -> roll miss chance, though the last two could probly be swapped with no effect.
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Offline Jackinthegreen

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Re: Mirror Image & Miss Chance
« Reply #3 on: March 31, 2013, 03:21:40 PM »
Considering miss chances negate natural 20's usually, it's probably better to roll miss chances first then do AC.

As far as MI and CoS, if the MI's also get the CoS miss chance then it'll be two miss chance rolls: One to determine whether it's actually you, and then one to determine whether the MI gets hit.  And then of course AC comes into the picture.

If the MI's don't get the benefit of CoS, then you have the first miss chance roll and if it's an 8 then you roll for CoS, and if that succeeds then it's on to AC.  If it's anything but an 8 then you roll for the MI's AC.

Edit:  Looks like the first is what the FAQ would have you do since the MI's do benefit from CoS.  Your math is correct, if ignoring AC.

Makes me want to get Henk the Child of Shadows stance.  lol
« Last Edit: March 31, 2013, 03:30:48 PM by Jackinthegreen »

Offline Garryl

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Re: Mirror Image & Miss Chance
« Reply #4 on: March 31, 2013, 03:42:52 PM »
Quote from: d20SRD
Enemies attempting to attack you or cast spells at you must select from among indistinguishable targets. Generally, roll randomly to see whether the selected target is real or a figment. Any successful attack against an image destroys it. An image’s AC is 10 + your size modifier + your Dex modifier.

Not only does the initial language suggest that the selection happens first, but the figments have their own AC.  That seems to me to imply that the order is: select target -> roll to hit -> roll miss chance, though the last two could probly be swapped with no effect.

Definitely that. Technically, I think you're supposed to, RAW, roll miss chances after the attack roll, but there are very few cases where it would matter, mostly for those few rerolls and action point things where you're supposed to declare it before the DM calls it a success or failure, so who cares. You certainly select your target (which of the caster and the various mirror images you're attacking) first, though.

Note that since the images are not, themselves, the caster (only appearing like him), they don't have his abilities or buffs, so some miss chances would not apply to them. I'm not sure I agree with the FAQ on whether purely visual miss chance effects like Blur and Displacement should apply (if you hit an illusion of an illusion-enhanced image, you're still hitting the illusion), but it's certainly reasonable. Likewise, Blink should work fine (50% of the time the caster just plain isn't there, so neither should the illusions), but miss chances based on reactive sorts of effects (can't think of any off hand except homebrew) shouldn't function.

Offline rot42

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Re: Mirror Image & Miss Chance
« Reply #5 on: March 31, 2013, 07:02:32 PM »
@OP: yeah, your math and reasoning check.

<snip>
Note that since the images are not, themselves, the caster (only appearing like him), they don't have his abilities or buffs, so some miss chances would not apply to them. I'm not sure I agree with the FAQ on whether purely visual miss chance effects like Blur and Displacement should apply (if you hit an illusion of an illusion-enhanced image, you're still hitting the illusion), but it's certainly reasonable. Likewise, Blink should work fine (50% of the time the caster just plain isn't there, so neither should the illusions), but miss chances based on reactive sorts of effects (can't think of any off hand except homebrew) shouldn't function.

Shadow Cloak, Drow of the Underdark 101 lets you get concealment as an Immediate action. I would not let an image activate that, so a clever enemy might deduce which image is real even if the attack misses. I guess that would apply to most Immediate actions, actually - only the Wizard can Abrupt Jaunt out of the way, only the Psion can manifest Evade Attack, and so on.

Offline zook1shoe

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Re: Mirror Image & Miss Chance
« Reply #6 on: April 01, 2013, 01:30:23 AM »
How about area effects for concealment? Like obscuring mist or blizzard?
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Offline rot42

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Re: Mirror Image & Miss Chance
« Reply #7 on: April 03, 2013, 08:11:03 PM »
How about area effects for concealment? Like obscuring mist or blizzard?

Even inanimate objects get concealment from those, so I would say that the images should benefit.