Integrate Miss Chance with AC?

[Quartz]

Has anyone done any work on integrating miss chances with AC? At the moment it's yet another die to roll.

It occurs to me that the miss chance is simply one special effect of AC, one that could be replaced by giving a Dodge bonus.

I was thinking along the lines of Blur being a straight +4 Dodge bonus, Displacement and Invisibility being a +10 bonus (~ 50% on D20), Mirror Image being +2 per remaining image, and so on.

To fit in with the standard (+1 to +5) progression, those bonuses might have to be halved. That's not so bad as it sounds because Dodge bonuses, unlike most others, stack.

We'd have to change the rule about magic items never giving Dodge bonuses.

Thoughts?

 

[Jeff Wilder]

It's not a linear function, so there would be some deformity of effect if you simply swapped miss chances for AC. (At least, this is what I think I mean ... I'm lousy at math. See below.)

A miss chance is more valuable to a low AC than to a high AC.

For example, consider ACs of 15 and 25 versus an attack bonus of +9.

Against the 15 AC, the attacker hits 75 percent of the time. Add in a 20 percent miss chance, and the attacker's overall percentage to hit the 15 AC becomes 60 percent (75 percent potential hits, less one-fifth that become misses). That equates to an AC bonus of +3.

Against the 25 AC, the attacker hits 25 percent of the time. Add in a 20 percent miss chance, and the attacker's overall percentage to hit the 25 AC becomes 20 percent (25 percent, less one-fifth). That equates to an AC bonus of only +1.

I quite like the interaction of miss chance and AC, so I wouldn't be up for simplifying. Just have the attacker rolls another d20 along with the attack roll ... since miss chances are in 5 percent increments, that should be easy and quick enough.

 

[Gerion of Mercadia]

The problem here is that miss chances are not directly correlatable to AC.

It's not a linear function, so there would be some deformity of effect if you simply swapped miss chances for AC. (At least, this is what I think I mean ... I'm lousy at math. See below.)

A miss chance is more valuable to a low AC than to a high AC.

Well, it is statistical probabilities. Concealment reduces the chance of being struck by anywhere from 10% to 50%. Furthermore, it can negate the dreaded "natural 20".

For a character who is hit on a d20 roll of 2 (95% probability) 50% concealment cuts this probability in half to 47.5%. In this situation, this is equivalent to an AC bonus of at least +10. If the character has a low enough AC such that he would mathematically be hit on a roll of 1, it is actually worth even more of an AC bonus.

At the other end of the spectrum, if a character can only be hit on a 20, (5% probability)50% concealment means the character is only hit 2.5% of the time. With RAW, regardless of how high an AC bonus you get, you can't reduce your probability of getting hit any lower than 5% by mere AC bonuses alone.

At any point between these "extremes" Concealment could be treated as an "AC bonus" - with regards to the probability of being hit with only a little "probability rounding error".

However, one of the added benefits of having concealment is that it can also negate certain special attacks - particularly Sneak attack and/or abilities such as the Assassin's "Death attack". If you treat concealment as a simple dodge bonus to AC, this added defence goes away.

To get concealment to "translate" into a direct AC bonus is highly situational, and an extreme headache. On top of that, it weakens the concealment ability.

IMHO, simply rolling the percentile dice along with the d20 to hit greatly speeds up the process for calculating "to hit" when concealment is involved. As a "dice rolling" convention IMC, if concealment applies, I have my players roll percentile for concealment along with the d20 to hit. Doesn't slow the calculation much, but it does slow the "roll" time by simply combining them.

 

[Azlan]

The only thing I dislike – intensely! – about "miss chance" is that it's given as a percentile, requiring the use of a d100. Since these percentiles are always in increments of 5, why couldn't they simply make "miss chance" roll-able on a d20? For example, a miss chance of 20% would be 1-4 on a d20, and a miss chance of 50% would be 1-10 on a d20.

Same goes for arcane spell-casting failure, when wearing armor. Oh, and for Pete's sake: how about rolling a 19 or a 20, on a d20, to stabilize when dying, instead of having to roll a 1-10 on a d100?!

I mean, is it the "d20 System", or ain't it? :\

 

[Jeff Wilder]

I mean, is it the "d20 System", or ain't it? :\

This was actually addressed in the run-up to the release of 3E. As stated, the idea behind the d20 system is that (1) a high roll is always good for the roller, and (2) d20 rolls all have a target number for success.

So, to avoid confusing things, they went with percentages for those areas of the rules like concealment and stabilization.

All that said, we're smart people ... we can use a d20 for this stuff if we want to.

 

[BASHMAN]

The only thing I dislike – intensely! – about "miss chance" is that it's given as a percentile, requiring the use of a d100. Since these percentiles are always in increments of 5, why couldn't they simply make "miss chance" roll-able on a d20? For example, a miss chance of 20% would be 1-4 on a d20, and a miss chance of 50% would be 1-10 on a d20.

Same goes for arcane spell-casting failure, when wearing armor. Oh, and for Pete's sake: how about rolling a 19 or a 20, on a d20, to stabilize when dying, instead of having to roll a 1-10 on a d100?!

I mean, is it the "d20 System", or ain't it? :\

Ummm.... there are people who actually roll this as a d100? I have always just used a d10 to do this (that's what you use in the Basic D&D set they came out with with 3.0 was new).

The only time I met someone who used d100 for this, he almost had a seizure when I rolled for two 50% miss chances, and rolled 2 d10s and got a 6 and a 6 and I said I hit. He said, "NO!!! YOU MUST ROLL FOR THE SECOND CHANCE!!!! THE FABRIC OF REALITY WILL UNRAVEL IF YOU ROLL BOTH MISS CHANCES AT ONCE WITH ONLY SINGLE D10s"

After a galleleo vs. pope moment, of me attempting to convince him that 1-5 on a d10 was mathematically the same as 1-50 on a d100, (and while we're at it 1-3 on a d6, heads on a coin, etc) and his complete obtuseness to it, I gave up on that game.

 

[Bayonet_Chris]

Miss chance

In my games, my to-hits are based on degree of success rather than 1s always miss and 20s always hit. Any miss penalty is applied directly as a -1 per 5% and it works out just fine.

When someone is completely concealed, a sense check (listen usually, sometimes spot or search if the situation warrants it) can be made to locate the "right square" so an attack can be made. I've never had a problem with it.

 

[Primitive Screwhead]

I too like the combination of AC and miss chance. Melding the two would result in just another class of insanely high AC opponents. Having a low AC opponent with a miss chance makes for an more dangerous encounter than ramping the AC up. YMMV.

Also, regarding the % rolls. One of the core concepts in the D20 system is that D20 rolls have a target number and can be modified. D100 rolls are not to be modified, left at a straight percentage check.

 

[Aust Diamondew]

After a galleleo vs. pope moment, of me attempting to convince him that 1-5 on a d10 was mathematically the same as 1-50 on a d100, (and while we're at it 1-3 on a d6, heads on a coin, etc) and his complete obtuseness to it, I gave up on that game.

LOL, I haven't met anyone that bad at comprehending basic probability in a loooong time, ever actually, took me a long time to convince some one that rolling a 12 on 2d6 is less likely to happen than rolling a 7 on 2d6 or a 12 on 1d12.

In response to the OP I'd recommend just rolling an extra dice with every attack, probably a d10 and just assign the right probabilities. Alternativley just have the defender rapidly roll d10s in sequence and he tells the attacker which of his attacks miss before he rolls them (such as attack 1 and 4 miss because of displace/blur, so the attacker only rolls attacks 2 and 3).