Mechanics thread

So I've been asked for details of evasion over PM, and don't want to have to keep giving single replies to more people in future, so since I don't think it's all been laid out in one place yet, it will be here.

Evasion in PoE is not fully random.

Each entity in the world contains an 'evasion entropy' value, between 1 and 100. The higher this value is, the more likely they are to be hit by the next attack. The initial value is random.
Every time something attacks you, they calculate their chance to hit as a percentage. That value is added to your evasion entropy. If the result exceeds 100, you're hit, and 100 is subtracted from the value. If the value hasn't reached 100, you're not hit.

Before anyone starts clamouring that they're not getting their actual chance to hit/evade, let's examine this mechanic in a bit more detail. Take the simple example of 100% chance to hit. Since you always add 100 to the entropy, it'll always exceed 100, and thus always hit, which is correct. The case of 0% chance to hit can similarly be trivially shown to be correct.
So let's look at 50% chance to hit. Since the initial value is random from 1-100, there's a 50% chance that the initial entropy value is higher than 50%, in which case adding the 50 from chance to hit will exceed 100 and thus hit, and a 50% chance the value is 50% or less, in which case adding 50 will not exceed 100, and thus not hit. So the first hit has a 50% chance to hit, as it should.
The second hit also has a 50% chance to hit, but will never hit if the first one does - provided you're only getting hit by things with 50% chance to hit you, you'll evade every second attack, and be hit by the others.
Let's say the initial entropy was 42. The first hit increases this to 92, and misses. The second raises it to 142, hitting, and then subtracts 100 from the value, leaving it back at 42.
I'll leave other percentages as an exercise for the reader, but they all work out - if an attack has 25% chance to hit you, every fourth attack will hit, and so on.

This is the mechanic by which streakiness is removed from evasion - it removes the possibility of failing to evade happening to come up several times in a row due to bad luck. Each attack has the correct chance to hit, and will hit you just as often as you'd expect in the average case using a purely random system, but the possibility of occasional but devastating non-average results - such as being hit by four consecutive attacks with only 10% chance to hit each - have been eliminated.

Some caveats:
1) If an attack would crit you, evasion is tested a second time, and if you evade, the hit is downgraded to a non-crit (it does not miss, since it's already tested for that and hit). This roll is purely random and does not increase the entropy value - it just generates a number from 1 to 100 and compares to the chance to hit. Details of why are in the spoiler.
Given that this, if it occurs, would always be the next evasion test after the one to see if it hit, then if this did use the entropy value, then having above 50% chance to evade would make you immune to critical strikes, since you can't fail two successive evasion checks on entropy if their chance to hit is below 50%. If you were hit, that means you just failed the evasion check to evade the attack, and thus the entropy is such that the second test would be unable to hit you, and the crit would downgrade, whereas if it failed to hit in the first place, then critting or not is irrelevant.
While the concept of being so evasive you can't be crit is cool, the above behaviour is undesirable, and so checking chance to hit for the purposes of confirming a crit should actually stay a crit does not test entropy. Testing chance to hit for the purposes of actually hitting is always done via the entropy value.

2) Whenever the entropy value would be used, if a certain short amount of time has passed since the last time this occurred, a new random initial value is chosen. This prevents the player from waiting near a weak enemy until it hits (leaving them on a low entropy value), then running to a boss fight, to start knowing they'll have the maximum number of attacks evaded before they get hit. Entropy will perform it's function as long as you're continuously being attacked, but don't expect to transfer it from fight to fight.
soul4hdwn wrote:
so by that pattern, if an attempt to evasion fails (token not add up over the specified eva value), then block and dodge have thier own constantly cycling entropy but only happening if the previous damage dodge failed.
No. Only evasion uses the entropy value. Dodge and block are completely (psudo)random.
Note that the character screen shows your chance to evade a hit from an average monster of your level. Brutus is not average, and is a unique, so I'd be careful about hovering too close to the 50% line, as Brutus's chance to hit may be higher than the average mosnter the character screen compares against.
Last edited by Mark_GGG on Dec 10, 2012, 1:27:32 AM
Vipermagi wrote:
Crit Chance rolls a value between 1 and 100 when you use a skill. If the rolled value falls in the Crit Chance range, your skill Crits.
If a monster is cursed with Critical Weakness, then for that monster only, the Crit Chance range is larger.

Let's say you have 10% Crit Chance, so rolling 1-10 gets you a Crit.
If you roll a 12, any non-Cursed monster hit by the skill is not Critted (12 is higher than 10). You will Crit on a Cursed monster however (10+5 is 15, 12 is lower than 15).
Ie. the Crit roll is done per cast, but the check is done per monster.
Pretty much this. Critical strike chance is checked separately against each monster, but the value rolled for that chance is rolled only once, and the same value checked against your chance to crit each monster.
Jezabel wrote:
Concerning the damage pets deal
I'm going to answer this assuming you mean minions, note that if you're actually talking about totems or something these answers are wrong.
Jezabel wrote:
from the flat elemental damage buffs on Anger and Wrath. Do they get increased 3 ways? Leveling the gem
Levelling the aura will increase the damage it adds to the minions attacks, yes. Some minion gems may grant larger % increases to minion damage as well (or at least smaller penalties). Zombies and Skeletons, to my knowledge, only change base minion damage as the gem levels, thus having no effect on the added damage.
Jezabel wrote:
+elemental damage passive nodes and item stats specifically stating +elemental damage
Your minions don't have any passive skills, nor items, so can't benefit from passives skills and items increasing elemental damage. The only exception is Necromantic Aegis, which allows minions to use item stats from your shield, in which case % increased elemental damage on that shield will increase the elemental damage dealt by the minions.
Jezabel wrote:
and resistance and elemental weakness debuffs of enemies?
Lowering the resistances of enemies will increase how much elemental damage they take form any source, including minions.
Jezabel wrote:
because the minions themselves cast the boom from MI, my own passives do not affect that? :(
Correct. But you can get passives that increase the life of and damage dealt by your minions, which will in turn have an effect on the Minion Instability explosion.
soul4hdwn wrote:
also remember, evasion then block then dodge, before taking damage.
Dodge is before Block. You can't block a hit that fails to connect in the first place.
Glowyrm wrote:
As for this part, the only thing I don't understand is what Mark means by "...and compares to the chance to hit". He seems to be talking about that random number that isn't Entropy, but how is it "compared" to hit?

Going by this little bit from the main post...

"This second roll is the same as the regular hit roll above (accuracy vs evasion)."

The 2nd roll works the same (according to the OP) but without Entropy (according to Mark). If the 2nd roll is a random 1-100 number, where does the chance to hit come in? How does it interact with that random 1-100 non-Entropy number?
That's how you implement a random chance for something to happen.

There's a set chance to hit (this is calculated from attacker accuracy and defender evasion).
To test that chance, you roll a random number from 1 to 100* and compare that to the change to hit. If the roll is equal to, or lower than, the chance to hit, you count that as a hit. If it's higher than the chance, you do not.
So, if the chance to hit is 100%, you always hit (because any number from 1-100 is <= 100).
If the chance to hit is 0%, you never hit, because no number from 1-100 is <= 0).
If the chance is 50%, then half of the time you'll hit, because exactly half of the numbers from 1-100 are <= 50.
And so on for other values.

When testing evasion to see if we hit, we use the entropy system as previously described, to remove streaks, but in general, if you have X% chance for something to happen, at random, and need to know whether that thing should happen this time, you do that by generating a number from 1-100 and comparing to X.

*actually 0-99, but I find people understand 1-100 better, and the only thing that changes whether an equal value counts as a hit or not.
WUlf1337 wrote:

You dont cast traps you lay them. This is why you need the trap knode "lay down speed" which affect only the speed to set them up. - as u alrdy mentioned. You cast spells, attack with attacks and lay mines/traps.

That's completely contrary to my in-game evidence. How about you stop regurgitating useless info?
He's 100% correct. Laying traps is affected by trap laying speed, and completely unaffected by cast speed.
When a trap triggers, if the trapped skill is a spell, cast speed will affect how fast the trap casts the spell.
Freekee wrote:
When I link Faster Casting to Bear Trap, the tooltip reflects a shorter cast time. Perhaps a tooltip error?
The spell, when cast, does have a shorter cast time. Laying the trap is not casting the spell. The trap casting the spell when triggered is casting the spell.

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