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Hello friends!
I was reading a thread about a 3.5 variant in which players roll to dodge attacks as opposed to creatures making attack rolls against them. This has the player rolling more dice and (ideally) getting the players more engaged in combat.
While interesting, I decided it wasn't for me or my group.
BUT it got me looking at the math behind AC and the "+10" caught my eye
"What if instead of adding a flat +10 to AC, you rolled a d20 and added that?"
So, I made an spreadsheet of what I am calling Fluid AC to illustrate what this math looks like. (Please Note: I am not amazing at math nor spreadsheets so it is entirely possible I screwed up somewhere)
LINK to Fluid AC spreadsheet (I think you will have to make a copy of it in order to edit it.)
It looks like this makes attacks at lower bonuses slightly more effective while reeling back attacks at higher bonuses. This would apply to both players and the creatures they would square off against.
I am not sure I would permanently adopt it into my home games but I would like to try it out!
Pros (in my opinion)
~"Getting to roll dice is the best part of the game!" ~Quote from someone who likes to roll dice
~Situations like "there's no way it can hit me unless it gets a 20/I will only miss on a 1" are a little bit harder to reach.
~A creature's AC isn't as obvious to the players. Before, if someone hits hit a 23 but the person the round before missed with a 22...
~The math still pretty close. Spells that lower/raise attack bonuses or AC still have value.
~Players could feel more engaged. Mr/Mrs Mega AC still has to roll when getting attacked and can't just take a nap when it isn't their turn.
~Pretty easy to impliment. Works with Normal, Touch, and Flat-Footed AC. No need to do a bunch of math, simply reduce each type of AC by 10.
Cons
~"More dice to roll? Yeah, that sounds great. /sarcasm" ~Quote from someone who dislikes rolling dice.
~While in many cases the math is pretty close, it is still different. In some instances the difference beween the vanilla system and Fluid AC is close to 20%.
~Figuring out a creatures AC as a strategy and a natural part of the game that Fluid AC robs you of. (I disagree, with this but I have heard it from multiple people in the past)
~There are those who want to be able to invest in AC and know that anything (of an appropriate CR) won't be able to hit them unless they get crit. This of course alters goofs up those plans.
~Many house rules are made in an effort to speed up the game. With adding more die rolls, this will do the opposite.
Questions
Should this appply to CMD as well?
It would make sense to, no? Attack rolls are made to reach a target number and that ever present +10 is still calculated in!
Can I effect this d20 roll in any way?
My gut reaction is no. I hadn't even considered it when I was origionally thinking about this. Any ability that could allow you to/force you to roll multiple d20s multiple will become even better. If Hero points or a similar system is being used in your games then you have another option available to you especially when it is impreitive that that next attack misses you.
Could there be other reprecussions of using this?
Most definitely. I don't have a mind to know of every interaction (Classes/Spells/Feats/etc.) that would come into play. Though, on the surface (especially if you don't allow that d20 roll to be altered in anyway) it doesn't appear to be that major of a change. if you know something I don't please share!
Doesn't something like this already exist.....
I honestly have no idea. A quick google didn't turn it up if there is. Fingers-crossed that I haven't wasted my time!
So what do you think? It's something different and definitely not for everyone.
Is there some glaring problem that I don't realize?
Is there some terrible mathmatical error in my spread sheet that proves that this system would inadvertantly turn every player into cauliflower?
I put time into this and figured I would just throw it out into the community for consumption, critique, and discussion
(EDIT: to include example for clarification)
Two Goblins, Bloog and Smasher, get into a fight!
LINK to goblin stats
Bloog attacks Smasher with his shortsword
Bloog makes an attack roll (1d20+2) and gets 12
Smasher now makes a defensive roll (1d20+6[(+2 armor, +2 Dex, +1 shield, +1 size]) and gets 14
Bloogs misses Smasher because he did not meet or exceed Smasher's roll.
(EDIT 2: Just because)
A goblins AC now, instead of being 16, can be between 7 and 26
What you detailed is pretty much what the 3.5 UA described... replace the flat + 10 with a d20 roll + armor bonuses vs a D.C. Of monster attack +11. I've been using this for years, and highly enjoy it. A lot less paperwork and rolls on the DM part. It gets even more interesting when you add DR from armor and shields.
Or did I misunderstand?
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What you detailed is pretty much what the 3.5 UA described... replace the flat + 10 with a d20 roll + armor bonuses vs a D.C. Of monster attack +11. I've been using this for years, and highly enjoy it. A lot less paperwork and rolls on the DM part. It gets even more interesting when you add DR from armor and shields.
Or did I misunderstand?
I may have explained this poorly! xD
This would be opposed rolls rather than having the creature rolling to hit AC or players rolling to dodge looking for a DC.for example:
Byrd attack Thewms (oh no!)
Byrd rolls attack as normal: 1d20 + BAB + Enhancement + etc
Instead of trying to reach a static number though, Thewms rolls to see what that the target number is.
Thewms rolls 1d20 + Armor + Shield + Dex + Dodge + etc
Compare numbers and if Byrd meets or exceeds then it is a hit. nat 20s/1s only matter for the attacker.
Ok, makes sense. Seems complex and unnecessary, but that is admittedly my finite perspective. Play it out and see if others enjoy it, it looks... idk, intriguing(?).
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Give me a bit to mull it over and I'll try to be more constructive and objective. Thanks for sharing in any case, you never know where this may lead or what it may unintentionally inspire.
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I like the idea, and have even played with it a little in the past.
It increases the number of rolls the gm has to make.
If the GM's rolls aren't public, it allows for more easy fudging of the results - which can be good or bad, depending on your tables view of such things.
Makes it harder for someone to run out for a bathroom break, and some people don't like having to roll that much. I let them take 10 as normal if they needed to step out, or weren't interested in using the rule on their end.
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I like the idea, and have even played with it a little in the past.
It increases the number of rolls the gm has to make.
If the GM's rolls aren't public, it allows for more easy fudging of the results - which can be good or bad, depending on your tables view of such things.
Makes it harder for someone to run out for a bathroom break, and some people don't like having to roll that much. I let them take 10 as normal if they needed to step out, or weren't interested in using the rule on their end.
I roll behind a screen when I GM. I agree that more fudging possibilities become available to the GM with Fluid AC, which I don't mind. While it could definitely be abused, I would hope that the GM would use the power wisely, as with anything available to them!
I hadn't considered people needing to step away from the table. It doesn't happen often enough at my tables but I could see it being a bit of a snag. The allowing of taking 10 when not around is an excellent answer to that situation. Kudos.
I do find it obnoxious, as a GM, when I think I've balanced an encounter and a guy stands there with an extra 2 AC from Defense and all the sudden no one can hit him whatsoever; dissolving any tension the fight could have.
The other thing about this way of doing things is it adds tension for low rolls. Someone who rolls an 8 against a goblin, even if they have +6, knows they miss probably. This is sad because the player knows in advance what the result was.
This can really be considered for even weird things like climb checks (-10 from the wall, +D20) though then you've probably gone too far. (maybe though.. maybe that's good for some kind of psuedo-encounter.)
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I may go ahead and try this since it *could* allow for more cinematic encounters where when the guy defending rolls badly, it represents a shield-parry that was swung too early and left him open.
Side Note:
I put up a Reflex-Defense thread not too long ago; basically allowing the defender to Roll out of the way.
http://paizo.com/threads/rzs2ulcp?Fighting-Defensively-Dodge-Option
If you go this route, you may consider the above since it functions in a similar manner.
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Alternatively, while I don't know if I recommend it, I added "luck dice" in some sessions (a D3) where 1 = -1, 2 = +0, 3 = +1
This has the effect of obscuring DCs, ACs, and similar without messing with the system too much. That said, I didn't have the heart to stick with it. Maybe I'll try it again in the future with a D6 if the system becomes too static:
1 = -2, 2 = -1, 3,4 = 0, 5= +1, 6 = +2
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Honestly, if going with your system I'd consider the:
* If you win by 5 or more, here's a bonus
* If you win by 10 or more, here's a bonus
approach. This could add interesting tension against a high AC opponent where if you flub an attack and get knocked prone by a perfect "counter", you have to weigh whether to attack full bore or whether to look for an opening or something.
I have a home game tomorrow night of Rise of the Runelords. I am going to pitch it to my players and we may try it out. They are on book 4 (starts at level 8ish) so it will be some Low-mid tier play.
I'll report back later!
I also meant to add that if you wanted to switch it up, simply using Combat Facing for -2 when flanking, -5 when attacking the rear; you can get encounters to switch it up without having to add variance into the system.
I will probably eventually use this as -5 to ac is good for swarming dudes who can't seem to hit a PC and it allows the PCs more cinematic battles sometimes; or at least strategy regarding it sometimes.
With my admittedly mediocre knowledge of stats, I think that this method would actually make static bonuses more powerful, not less like it may seem.
In stats there is a theorem that says that when you add random numbers together, you get a bell curve. In layman's terms, a single D20 roll has an equal chance of both 20 and 1. However, with a 2d20 roll the chance of the sum being 2 or 40 is much less then the chance of the sum being 20.
The result is that characters that are usually only hit on 19s will be hit even less often, while characters with low attack bonuses will struggle to hit.
With my admittedly mediocre knowledge of stats, I think that this method would actually make static bonuses more powerful, not less like it may seem.
In stats there is a theorem that says that when you add random numbers together, you get a bell curve. In layman's terms, a single D20 roll has an equal chance of both 20 and 1. However, with a 2d20 roll the chance of the sum being 2 or 40 is much less then the chance of the sum being 20.
The result is that characters that are usually only hit on 19s will be hit even less often, while characters with low attack bonuses will struggle to hit.
I don't think this is correct; so I'll give a set of examples we could discuss:
Regular:
20 AC, +0 to hit
Hits on a 20 => 5%
Fluid:
10 AC, +0 to Hit => you have to beat their Dice Roll by 10 or more
So if the defender gets:
* 10, (20 wins => one result)
* 9 (19-20 wins => two results)
* [...]
* 1 (11-20 wins, 9 results)
which will give you 9 + [...] + 2 + 1 = 45 results out of 400
which is 11.25%
Regular:
17 AC, +0 to hit
Hits on a 17+ => 20%
Fluid:
7 AC, +0 to Hit => you have to beat their Dice Roll by 7 or more
So if the defender gets:
* 13, (20 wins => one result)
* 12 (19-20 wins => two results)
* [...]
* 1 (7-20 wins, 13 results)
which will give you 13 + 12 + [...] + 2 + 1 = 91 results out of 400
which is 22.75% chance to hit
Regular:
10 AC, +0 to hit
Hits on a 10+ => 55%
Fluid:
0 AC, +0 to hit => you have to beat their dice roll by 0 or more
So if the defender gets:
* 20, (20 wins => one result)
* 19 (19-20 wins => two results)
* [...]
* 1 (7-20 wins, 19 results)
which will give you 20 + 19 + [...] + 2 + 1 = 210 results out of 400
which is 55% chance to hit.
So the results when things are even are the same, but the variance at higher AC's relative to the attacker make it so that some attacks that would have failed will now pass.
Additionally, because of that, it's worth noting that this makes AC strictly worse under these rules than normal.
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With my admittedly mediocre knowledge of stats, I think that this method would actually make static bonuses more powerful, not less like it may seem.
In stats there is a theorem that says that when you add random numbers together, you get a bell curve. In layman's terms, a single D20 roll has an equal chance of both 20 and 1. However, with a 2d20 roll the chance of the sum being 2 or 40 is much less then the chance of the sum being 20.
The result is that characters that are usually only hit on 19s will be hit even less often, while characters with low attack bonuses will struggle to hit.
I'm not quite sure I am wrapping my head around what you are saying, but if you make a copy of that spreadsheet you can enter numbers to see what they look like with fluid ac vs vanilla.
I won't go over the math, but this method basically advantages whoever is weaker. This means it advantages the monsters in most cases (as an individuals strength is what is important not the group as a whole). Occasionally if the PC's face APL+4+ encounters, this will give them a chance to win it. However most of the time it will make it so the PC's need to stay on their toes a bit more. Do it to spell DC too. Cool stuff.
More rolls though, you may just want to say at the beginning of play that no effects that give more attack rolls are allowed (other than haste perhaps) build your character else-wise.
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With my admittedly mediocre knowledge of stats, I think that this method would actually make static bonuses more powerful, not less like it may seem.
In stats there is a theorem that says that when you add random numbers together, you get a bell curve. In layman's terms, a single D20 roll has an equal chance of both 20 and 1. However, with a 2d20 roll the chance of the sum being 2 or 40 is much less then the chance of the sum being 20.
The result is that characters that are usually only hit on 19s will be hit even less often, while characters with low attack bonuses will struggle to hit.
The bell curve occurs when you're adding the two variables together. That is not was is happening here. Instead, you're comparing the two variables to each other.
What actually happens is that someone with a lower attack modifier (or who normally needs to roll high to beat a static AC) hits more frequently, and someone with a high attack modifier (or who normally needs to roll low to beat a static AC) hits less frequently.
While you have more results concentrated towards the middle of the range of possible results, in this case the overall range of results is higher. For a standard d20 roll against a static AC, the range between the lowest possible result (a 1) and the highest possible result (a 20) is 19. But if both sides are rolling a d20, then the lowest possible result is 1 - 20 = -19 and the highest possible result is 20 - 1 = +19, for a range of 38 between lowest and possible results.
The bell curve would apply in a more intuitive manner if one side were rolling 2d10 or 3d6 or if each side were rolling a single d10.
So I dun gone and dids some maths. Have some charts!
The methodology is as such:
The big square contains the results of all the opposed rolls, where we subtract the defender's roll from the attacker's.
In row 28 we count up all the occurrences or each number.
In row 29, we sum the number of ways you can roll a given number or higher, then we add 20 (for natural 20s) and then divide by 400 (the total number of possibilities). This gives us the chance to hit under Fluid AC.
Then we have pretty graphs!
The TL;DR is that the attacker prefers fluid AC if the defender's bonus to AC is 4 or more larger then his bonus to hit.
The difference, when it exists is rarely more then about 10%
While you have more results concentrated towards the middle of the range of possible results, in this case the overall range of results is higher. For a standard d20 roll against a static AC, the range between the lowest possible result (a 1) and the highest possible result (a 20) is 19. But if both sides are rolling a d20, then the lowest possible result is 1 - 20 = -19 and the highest possible result is 20 - 1 = +19, for a range of 38 between lowest and possible results.
The bell curve would apply in a more intuitive manner if one side were rolling 2d10 or 3d6 or if each side were rolling a single d10.
I'm not sure where I went wrong in my mental model of dice rolls... Maybe it will make more sense in the morning.
The bell curve occurs when you're adding the two variables together. That is not was is happening here. Instead, you're comparing the two variables to each other.
This is incorrect. Comparing numbers is mathematically identical to subtracting them, and subtraction is basically addition :) Take a look at the graph labeled "Distribution of outcomes under Fluid AC" you will see a bell-curve! (a really pointy one).
I don't think this is correct; so I'll give a set of examples we could discuss:
So this looks correct to me, but the conclusion still felt off. Thus, you motivated me to make some charts instead of sleeping :D Thanks for correcting me!
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I have a home game tomorrow night of Rise of the Runelords. I am going to pitch it to my players and we may try it out. They are on book 4 (starts at level 8ish) so it will be some Low-mid tier play.
I'll report back later!
Our home game was last night!
I pitched this to my players and they agreed to try it out for the session.~everyone agreed that no number should be able to be applied to the defender's roll and that it couldn't be altered in any way.
~Everyone agreed that Fluid AC would apply to CMB as well.
~We took to refering to the opposed roll by the person being attacked as the Defensive Roll and the number being added to it as the AC Bonus, Touch Bonus, and Flat-Footed Bonus.
~After an example was given (apparently I am bad at explaining things xD) it was very easy for the players to grasp.
~It ended up not being as time consuming as I had originally thought it would be. When an attack was declared, both the attacker and defender would roll at the same time. Because the defender only ever had one number to add and the attacker had many (attack bonus, Inspire Courage, Flanking, Invisible, etc) the defender would be ready with the total before the attacker.
~The players, who are level 8, faced a few Creatures well below their CR, some CR 8, a creature that was CR 10 and a few traps ranging from CR 3 - CR 5. While there were a few instances where a high and a low Defensive roll made for some surprising moments, at no point did we feel that attacks were hitting too often or not enough.
~My players commented after the session that they never new for sure that any given attack would hit and always were kept on the edge of their seats but never felt cheated.
~A situation came up where one of the players needed to through a creature's square (CMB+5) and we used a Defensive roll. The player happened to fail when with Vanilla AC it would have been an almost guaranteed success. We knew this could happen and but this was definitely a WHOA kind of moment.
~One player mentioned how using Fluid AC made him feel like he had to be more tactical in his decisions in combat. (I don't quite understand, but he said it. haha)
~In the end all five of my players and myself agreed that it was a neat system and have decided to adopt it into regular play.
All this does is increases the variance. It's statistically identical to the attacker rolling 2d20-11 instead of 1d20 (and one of those dice is used to determine crits). So it increases the chance of getting extreme results, which (as Hogeyhead says) helps weaker combatants.
Does the defender's roll have any special effects on a 1 or 20?
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All this does is increases the variance. It's statistically identical to the attacker rolling 2d20-11 instead of 1d20 (and one of those dice is used to determine crits). So it increases the chance of getting extreme results, which (as Hogeyhead says) helps weaker combatants.
Does the defender's roll have any special effects on a 1 or 20?
That was something else that I had very briefly considered but ultimately decided not to try. Though, I am going to make a new copy of my spreadsheet to see what happens when 1s and 20s are handled differently!
Would there be anything you suggest?
Arguably, 1 is an auto-hit and 20 is an auto-miss. But for any balanced fight it's unlikely to make a huge amount of difference to what you've already got (a 20 for defence means +10 AC over normal, which is quite likely a miss).
You could use those results for critical- and fumble-like things, but that would make it even more random.
I like the version where players always roll vs. NPCs or monsters:
1) PC attacks a monster: Player rolls a normal attack roll.
2) Monster attacks a PC: Player rolls d20 + PC AC - 10 vs. 10 + AB.
3) PC uses a spell with a save: Player rolls d20 + DC - 10 vs. 10 + save bonus.
4) Monster uses a spell with a save: Player rolls a normal save.
That means the same amount of rolling in total, less for the GM, more for the players. And the players still don't automatically know the monster's values.
Damage etc. should still be rolled by the attacking creature - you don't want players to 'hurt themselves'.