Author Topic: Iterative probability and multi layer defenses.  (Read 6760 times)

Offline littha

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Iterative probability and multi layer defenses.
« on: July 14, 2012, 11:37:15 AM »
Iterative probability is important in D&D. Even if you only have a  1/20(5%) chance to fail that fort save against Disintigrate eventually you will fail and get turned to dust unless you have some other defense.

Lets say you have that 1/20 chance of failing your save, probability is worked out by multiplying together individual cases. For example, the second disintigrate still has a 1/20 change of killing you but the total chance of failing one of those is actually around 90%.
You work this out this way:
First you work out the chance of failure:
1/20 = 0.05
then invert that so you have the chance of success
19/20= 0.95
Then multiply the chance of success together to get the chance at succeeding both saves:
0.95*0.95= 0.9025
Which is around 90% so a 10% chance that one or the other killed you. It also works for more repetitions:
0.95*0.95*0.95*0.95 = 0.81450625
80% or so means thats a 20% chance of death.

The problem in D&D terms is that as an adventurer you will be targeted hundreds if not thousands of times over your level 1 to 20 career and the probability of you failing one save is enormous even with the highest possible bonuses to your saves, however there are solutions.
First is getting your saves to that magical 1/20 chance. This can be achieved with magic items or spells usually but high base saves and good Dex/Con/Wis help too.
Class specific ways of boosting Saves:
(click to show/hide)

Rerolls certainly help because they make the chance of a failed save much lower. The same 1/20 failure chance results in around a 0.25% chance of failure if you have a reroll rather than 5% which is an enormous increase in survivability.
(click to show/hide)
There are also abilities that allow you to ignore that 1/20 chance of failure once you get your save high enough.
(click to show/hide)

Next there are the abilities that make your saves more effective, Evasion and its rarer cousin Mettle are their general names and they really help survival some of the time. Both can be gained through class levels but Evasion can also be had from items.
(click to show/hide)

« Last Edit: July 19, 2012, 09:46:08 AM by littha »

Offline littha

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Re: Iterative probability and multi layer defenses.
« Reply #1 on: July 14, 2012, 11:47:28 AM »
The second section of this guide focuses on AC.
This is generally not a good defense for several reasons but mostly it is because attack bonuses scale with level and magic items when AC generally only scales with items.

Touch AC can however be boosted to a decent level and even your normal AC has its uses at lower levels.

First general AC bonuses, these are not all that useful past a certain level (5-8) unless you want to spend the vast majority of your gold on it because while it is rather hard to push your AC past about 28 a monsters (or Players) attack bonus will keep going up rapidly. Many mid to high level monsters have attack bonuses of more than 35 or 40 so the chances are they are going to be hitting you. What having a High AC does do however is reduce the amount that they can Power Attack for while still being certain of a hit and this in turn reduces the amount of damage you take by a bit.
AC bonuses:
(click to show/hide)

Touch AC bonuses:
(click to show/hide)
« Last Edit: July 14, 2012, 12:21:44 PM by littha »

Offline littha

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Re: Iterative probability and multi layer defenses.
« Reply #2 on: July 14, 2012, 11:47:39 AM »
As above AC is not really a good defence against melee attacks past about level 10 (Even that is pushing it) but there is a way to stop that dragon from smashing into the floor and that defense is miss chance. Miss chances are however a lot easier to come by for mages so this is one of the reasons melee suffer so much in this game.
Miss chances are generally gained through spells and concealment
(click to show/hide)
« Last Edit: July 19, 2012, 09:37:38 AM by littha »

Offline littha

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Re: Iterative probability and multi layer defenses.
« Reply #3 on: July 14, 2012, 11:54:47 AM »
The next Section of the guide focuses on Critical Hits.
« Last Edit: July 19, 2012, 09:46:28 AM by littha »

Offline littha

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Re: Iterative probability and multi layer defenses.
« Reply #4 on: July 19, 2012, 09:38:02 AM »
Immunities are a strong defence, they are sometimes harder to get but being completely immune to an effect is awesome.

Fire and Cold subtypes grant immunity to their related damage at the cost of a 50% increase in the other. It is possible to get both subtypes which makes you immune to both. Then there are creatures that are immune to damage types without the subtype like demons.

Fire and Cold
(click to show/hide)

Other Elemental immunities
(click to show/hide)

Affliction immunities-
Stun
Paralyze
Sleep
Disease
Death Effects
Ability Drain
Energy Drain
Ability Damage
Mind affecting
Poison

In addition if you have a constitution score of - you are immune to any effect that requires a Fort save and does not affect objects.
« Last Edit: July 19, 2012, 09:55:23 AM by littha »