Miss chances from different sources

[heavyfuel]

So, what if I have miss chance from 2 different sources, say, the Swiftblade's Blurred Alacrity (http://archive.wizards.com/default.asp?x=dnd/prc/20070327) and the Martial Stance Child of Shadows?

The Swiftblade says the miss chance doesn't stack with other spell effects. Since Child of Shadow isn't a spell, should they stack? And how would they?

I found this 2010 thread (http://www.giantitp.com/forums/showthread.php?143875-3-5-Stacking-miss-chances)discussing the subject, but there was a disagreement on whether or not Rules Compendium's rule should be used. There was also mention of a "Rules of the Game" article there. If anyone knows which one, it would be much appreciated.

Let's try to keep answers as RAW as possible. Thanks!

[GilesTheCleric]

This (http://archive.wizards.com/default.asp?x=dnd/rg/20041005a) seems likely:


Normally, miss chances do not stack (a blur spell's 20% miss chance doesn't stack with the 50% miss chance for being completely unseen, for example). In this case, however, you could combine the incorporeal miss chance with a miss chance for attacking a concealed target because one involves uncertainty about exactly where the target is and the other involves an immaterial target that might not vulnerable to the attack at all. To stack the miss chances, check the miss chance for concealment first, then check the incorporeal miss chance; if the attacker fails either miss chance, the attack misses (to save time, you might want to check the highest miss chance first, or just roll both of them at the same time).

I'll note that the "Rules of the Game" articles don't always describe the actual rules of the game, so take them with some salt.

[Troacctid]

Generally, only the highest miss chance applies unless the effect states otherwise. Mirror Image is an exception, for example.

[Thurbane]

AFB at the moment, but I think Rules COmpendium addresses this fairly specifically?

[Crake]

This (http://archive.wizards.com/default.asp?x=dnd/rg/20041005a) seems likely:



I'll note that the "Rules of the Game" articles don't always describe the actual rules of the game, so take them with some salt.

On top of incorporeal miss chance, you could have blink as well, for a total of 50% (concealment), 50% (incorporeal) and 20-50% (full on ethereal), all being based on different reasons for the miss chance. Concealment for striking the right place, incorporeal for the attack hitting, but not actually affecting, and ethereal for being there at all. All that combined would reduce the chance of being hit to 12.5%


AFB at the moment, but I think Rules COmpendium addresses this fairly specifically?

According to the rules compendium though, incorporeal miss chance and concealment do not stack.

[Troacctid]

According to the rules compendium though, incorporeal miss chance and concealment do not stack.
Yes, that's correct.

[heavyfuel]

I'll have to talk with DM, but the he tends to be pretty straight forward with RAW, except in stupid cases.


This (http://archive.wizards.com/default.asp?x=dnd/rg/20041005a) seems likely:

I'll note that the "Rules of the Game" articles don't always describe the actual rules of the game, so take them with some salt.

Assuming he allows for them to stack. Is there a way to calculate the odds with a single d100 roll? Instead of rolling one at 50% and another at 20% chance, could he just roll one with XX%? How much would XX be?

[Troacctid]

I'll have to talk with DM, but the he tends to be pretty straight forward with RAW, except in stupid cases.
In this case the rule is pretty unambiguous.


Assuming he allows for them to stack. Is there a way to calculate the odds with a single d100 roll? Instead of rolling one at 50% and another at 20% chance, could he just roll one with XX%? How much would XX be?
Multiply them together. 50% x 20% = 10%

[John Longarrow]

for 50% miss chance, you have a one in two chance of hitting.
Out of that one in two, you have an 80% chance of hitting.

.5 x .8 = .4

You have a 40% chance to hit, statistically.

[Zombimode]

So, what if I have miss chance from 2 different sources, say, the Swiftblade's Blurred Alacrity (http://archive.wizards.com/default.asp?x=dnd/prc/20070327) and the Martial Stance Child of Shadows?

The Swiftblade says the miss chance doesn't stack with other spell effects. Since Child of Shadow isn't a spell, should they stack? And how would they?!

This is not really a question of stacking miss chances. Neither of those abilities actually provides a miss chance. Instead both abilities provide concealment. And the main effect of concealment is a 20% miss chance.

This should also answer the question of stacking. As there is no general rule that more then one instance of concealment provides any additional benefit, any instance of concealment beyond the first i simply redundant.

[Crake]

This is not really a question of stacking miss chances. Neither of those abilities actually provides a miss chance. Instead both abilities provide concealment. And the main effect of concealment is a 20% miss chance.

This should also answer the question of stacking. As there is no general rule that more then one instance of concealment provides any additional benefit, any instance of concealment beyond the first i simply redundant.

Oh, definitely, the discussion just kinda diverged to different kinds of miss chances after a point.

[rrwoods]

In this case the rule is pretty unambiguous.


Multiply them together. 50% x 20% = 10%
Not quite, you need to multiply the success chances together, not the miss chances.
1 - ((1 - .5)*(1 - .2)) = 40%.

In general if the miss chances stack, your final miss chance is
1 - product(1 - x)
where each x is a miss chance.

[Troacctid]

Not quite, you need to multiply the success chances together, not the miss chances.
1 - ((1 - .5)*(1 - .2)) = 40%.

In general if the miss chances stack, your final miss chance is
1 - product(1 - x)
where each x is a miss chance.

Oh, right, yeah, brain fart, sorry.