For a long time, many mechanisms in PoE have not been disclosed in detail in the wiki, causing players to dispute on many issues. In order to answer queation that players feel uncertain, poe has compiled a mechanism Q&A guide, don't miss it!

 

Does Rupturing's "Bleeding on [ruptured enemies] expires 25% more quickly" affect bleeding in the same way as "Bleeding you inflict deals damage x% faster" mods? Does it stack multiplicatively?

Not quite, but the total effect of rupture is similar despite these applying to different things at different times. Modifiers that cause ailments to deal damage faster modify the damage per second multiplicatively (just like a "more damage" modifier), and apply the inverse modification to the duration, so that the total expected damage of the ailment stays the same. Multiple 'deal damage faster' modifiers stack additively with each other.

Modifiers that affect how quickly things expire do not affect the magnitude of the effect at all, and technically do not modify the duration, they make time be tracked differently for that effect. The most common example is Temporal Chains, which you can see in-game does not affect the numerical duration of buffs/debuffs on you, but makes their timers tick down more slowly.

If you inflict Bleeding that would deal 100 damage per second for the default 5 seconds, but have "Bleeding you inflict deals damage 25% faster", that applies 25% more damage per second, and the inverse of this modifier to the duration, resulting in inflicting a bleeding that deals 125 damage per second for a 4 second duration; the total expected damage is still 500. These are the values applied to the enemy in the debuff.

If that enemy is Ruptured, they have 25% more damage taken from bleeding, and the bleeding expires 25% more quickly. So assuming no other modifiers, they would be taking 156 damage per second, and the Bleeding debuff's "4 second" timer would tick down faster, resulting in it expiring after only 3.2 real seconds have passed, and thus dealing a total of 499 damage - 1 having been lost to rounding.

Note that the modifiers from Rupture are dynamic - a bleeding enemy starts taking more damage when they become Ruptured and ceases to do so when Rupture expires, and similarly, a bleeding enemy that becomes ruptured will have the timer on their bleeding debuff speed up, and return to normal speed if rupture is removed.

When mines are detonated while wielding Tremor Rod with a max mines of 20, should the detonated chain be 20 or 40 mines long? Is this dependent on the re-arming time of the mines? If more mines are thrown during the duration of the detonation sequence will those mines delete existing mines like they would before they were detonated, or can re-arming mines not be deleted?

It's mostly dependent on the cast time of the spell the mines use, although re-arming time is also a factor, as is how they're placed. Mines cast spells (or use attacks) just like players do, which takes the cast time of the spell or attack time of the attack. They are "front-loaded" such that the effects of the skill happen right near the start of this time so most of the cast time for mines is follow-through rather than build up, but the total cast time stays the same, and unlike players mines can't try to animation cancel to skip part of the animation. Once a mine finishes casting it's skill, it either immediately dies or starts to re-arm. Re-arming, just like initially arming the mine before it can use a skill the first time, takes a base time of 0.5 seconds, affected by modifiers to mine arming speed. Only after both of these are done can it be detonated to use the skill again.

At the point a mine is detonated, it looks around it for other mines in range to add to the detonation sequence. These must be in-range of the detonating mine, and must be ready to use their skill at that time.

Mines that are alive always count towards the limit and will be replaced if you create too many. The only time a mine stops counting towards that limit is when it dies.

Why are kills via hit always credited to the killing entity (e.g. a monster killed by the initial hit of fire trap will give life-on-hit to the trap not the player), while kills via DOTs applied by anything are always credited to the player (the degen of fire trap, or poison applied by a zombie, etc). Wouldn't it make more sense to also credit DOT kills to the applying entity?

Because hits are immediate and thus there's an implicit guarantee that the thing dealing the damage exists at the time the thing taking the damage dies. The direct effects of the kill can be assigned to that object, and some things, such as experience, can be "passed up the chain" because the game can ask that object who is ultimately responsible for things it kills.

Damage over time is caused by applying a debuff to another object - after which the debuff is attached to the target, but independent of the thing that applied it.

When your minion, totem, trap, etc inflicts a damage over time debuff, if the debuff was set to identify the minion as the killer, that object may have been deleted by the later time when something dies to that damage over time, in which case the kill could not be correctly assigned - the object that actually killed no longer exists, so it can't be given the direct effects of having killed something, and neither can it be queried to find another object it has a relationship to for passing experience, etc up to. In some cases, a newly-created object might have re-used that id, which would make things extra weird.

This also gets extra weird in cases with conversion trap, since that makes you ultimately responsible for kills by a converted monster, but only while it's converted - if it unconverts before the kill, that kill would be assigned to the monster itself, or its owner if it's a minion/totem/etc. So even when objects exist, the fact that the chain of "kill ownership" can dynamically change.

There are long term plans for a more complicated system that will be able to track whole chains of these relations as they dynamically change so that it in such cases it can skip applying any direct effects but still maintain the parts of the kill ownership chain for things that do exist and correctly "pass up" things like experience. But for now this is a mostly-harmless bug that has some slightly weird consequences but doesn't disrupt anything very much, and is far superior to players missing out on those kills entirely, so this isn't a high-priority fix.

Phase Run's secondary buff has a 0.2 duration and activates when you use a skill. Does the buff apply to the skill regardless of how long it takes to get the skill out, or would I need to finish my attack before the buff expires for it to apply?

You need to have the buff at the time the skill calculates damage, which is ultimately dependent on the skill in question, and as such there is no one-size-fits-all answer. Strike skills, and several other melee skills, will calculate damage against things in range when the skill starts (with the exception of flicker strike since it can't do that until it teleports), so those will tend to always benefit, and is what the buff was largely designed for. 

If I have Body Armour with the following modifiers:
- 2% additional Physical Damage reduction "of Dampening"
- 10% Physical Damage from hits taken as Cold Damage "Redeemer's"
- 4% Reduced Cold Damage taken
and I take a Physical hit for 10000 damage, what is the order of the damage reduction? How much damage am I going to take?

You take the damage as 9000 physical and 1000 cold. Assuming no other relevant stats, your physical damage reduction applies to the physical damage, and the reduction to cold damage taken applies to the cold. You would thus take 8820 physical damage and 960 cold damage, for a total of 9780 damage.

How does Petrified Blood interact with Ichimonji's "10% increased Effect of Buffs on you"?

The numerical magnitudes of the buff are increased by 10%. Assuming a level 20 gem with no quality, this results in a buff that causes 44% of life loss below half to be prevented, 89% of that prevented loss to be lost over 4 seconds, as well as adding base life cost to skills equal to 44% of base mana cost while not on low life.

Does generic AOE affect modifiers such as the Ignite Spread from Berek's Respite?

No.

Note: This answer has been edited as the original answer was incorrect.

What are the ailment thresholds formulas for Brittle, Scorch and Sap? How do I know the magnitude of the ailment applied?

Scorch is the same as shock and chill; the magnitude is given by the formula: 50 * (Damage / ailment threshold)^0.4
Brittle is the same as above, but the multiplier number at the start is 25 instead of 50. (Actually it's 2500, but that's because the stat Brittle inflicts stores 100 times the value applied, so that it can hold 2 decimal places - so internally Brittle's maximum magnitude is 1500, which causes +15% to crit chance against the enemy - for general purposes it's simpler to think of it as 25 and ignore the extra factor of 100).
Sap is the same but with 100 / 3.

How do stacked dodge, evade, and blind miss chances apply when a mob tries to hit an exile?

Attacker accuracy is compared to defender evasion to work out the chance to hit. If the attacker is blinded, this chance is 50% lower.

The chance to evade is inherently the inverse of this (chance to evade = 1 - chance to hit).

Evasion is tested using the above chance to evade and the entropy system, which has been discussed elsewhere at length.

If the hit was not evaded and the defender has a chance to dodge, this is tested (dodge chance is completely random).

Does dodge reset evasion entropy?

I don't understand what this means, exactly. But Dodge is entirely separate from evasion and does not interact with it, or the entropy value. If a hit is not evaded, dodge chance is tested to see if it is dodged. If a hit is evaded, dodge chance is not checked because there would be no point.

Is there an interaction between Awakened Spell Echo and Summon Skeletons with the Dead Reckoning jewel?

A skeleton is not a repeat of a skill, and damage dealt by the skeletons' melee attacks or spells is dealt by that skill, not by the summon skeletons skill. The final repeat of summon skeletons technically has a chance to deal double damage, but since the summon skeletons skill cannot ever deal damage, this doesn't do anything.

Can increases to "damage with skills that cost life" still apply to skills that do not cost life? For example, triggering Exsanguinate or reducing its life cost by 100%?

Triggering a skill does not change its cost, you just avoid paying that cost. But a skill with a cost of 0 life does not cost life.

What is the priority between all kinds of explode and destroy corpse effects (e.g. cluster jewel notable with destroy on kill, crusader's explode mod, Inpulsa, Profane Bloom)? Do they all happen at once? Do they cancel each other?

All applicable effects will apply.

Some of the Lord of Steel variants have this line:

"Call of Steel causes (40-50)% increased Reflected Damage"
My understanding of impale damage is that, once stored, it is not modifiable by your damage stats, yet clearly this is an exception. With that in mind, what is this "increased Reflected Damage" additive with?

Call of Steel does not cause the impales to deal damage, it deals reflected damage itself, looking up the amount of damage each impale has stored to work out the base amount of that damage. Reflected damage is only modified by things that explicitly modify reflected damage. Currently I don't think that there are any modifiers available to players that can affect this specific reflected damage except for this one.

In what order do the effects from Steelskin, Frost Shield, and Jinxed Juju occur? If there isn't an order of operations, how does the game deal with situations where the damage taken from sources that aren't your life is above 100%? i.e. if a character had "Mind Over Matter", "Molten Shell" and "The Jinxed Juju", bringing the total damage from hits taken from other sources than life to 115%.

Jinxed Juju ("from your Spectres' Life before you") gets in first, changing which object the damage takes from in the first place - note the lack of any reference to Life or ES specifically, as this is before any consideration of what resource is lost to damage, only determining which objects the damage affects.

Frost Shield ("from Frost Shield before your Life or Energy Shield") is next, being more specific in that the damage is affecting specifically your life or ES, but still taking precedence over any buffs on you because this is taking from an external object, rather than a separate resource you have.
At this point all the damage that's left is taking something from you, rather than other objects, and further modifiers just change which resources are taken from.

Aegises ("from the Buff before your Life or Energy Shield") go next, having priority over Guard skills because they are an absolute effect which affects all damage (of the appropriate types) rather than a percentage of it - they don't have a percentage value that could be summed with a guard skill in any way, they just take all of it. You can't have multiple Aegises that affect the same damage (or at all), so there are no conflicts here.

Then there are the Guard skills ("from the Buff before your Life or Energy Shield"), which are like the aegises but only for a percentage of the damage. In theory if you have multiple guard skills active at once, they should apply additively with each other, but this is not possible, so the game doesn't actually handle that case.
At this point, all the "extra" resources are done with and all the damage that's left is taking from your life, mana or energy shield, specifically, and further modifiers only change which of these three is taken from.

Your Energy Shield steps up first, but chaos damage bypasses it.

After ES, Mind over Matter and similar effects ("before your life") have a final chance to jump in after ES but before life to siphon off some of the loss.

Then what remains is taken from life, although Petrified Blood can prevent some of the loss of life.

If there's still any excess damage that hasn't taken something away, it isn't your problem at this point on account of you being dead, because that means you ran out of life before you ran out of damage.

Physical damage reduction typically applies to hits e.g. Overwhelm. Poacher's mark, however, applies a debuff that lowers the enemy's physical damage reduction. Does this work with DOTs like Exsanguinate and bleeds?

Armour only gives Physical Damage Reduction against hits, but Physical Damage Reduction in general applies to all physical damage taken. You just need to get it from something other than armour.

[Extra clarification]: Physical Damage Reduction, unlike resistances, cannot go below zero - so the enemy must have some physical damage reduction that applies against DoT (i.e. not from armour which only provides it against hits) in order for Poacher's Mark lowering it to affect a DoT.

For skills that specify "modifiers to x also apply to this Skill's Damage over Time Effect," would this also apply to things like ignite, poison or decay damage?

No. "This Skill's Damage over Time Effect" refers to the specific effect caused by that skill, not to any other damage over time.

Why does "Increased Global Physical Damage" (or currently called "Increased Physical Damage") scale poison damage from Physical Skills? If I understand correctly, Poison base damage is a percent of the base damage dealt, which is calculated before any increased/more multiplier. The damage dealt from Poison is Chaos, so it shouldn't scale with any increased/more multiplier to Physical damage at all. Could you explain the logic behind this mechanic?

Damage causing ailments is similar to conversion - you're using base (and added) physical damage to cause chaos damage over time. This gets modified by modifiers that apply to either. So in this case, physical damage modifiers, chaos damage modifiers, and damage over time modifiers all apply. However, modifiers specifically to "physical damage over time" would not apply, because the damage never fit in that category at any stage.

For a more visual explanation, see my post here from when we changed ailment calculation to remove double dipping. The "New System" images are still accurate, and the second one in particular deals with a case where you are able to ignite with cold damage, and have base physical damage converted to cold, showing how the cold damage hit and fire damage ignite are both calculated independently from the same base physical damage.

Is damage from traps subject to the penalty from the Blizzard Crown implicit Your Hits Treat Cold Resistance as 10% higher than actual value?

Yes. "Your Hits" includes all hits from your skills, and traps are using your skills.

Does Life Recovery Rate benefit energy shield regeneration granted by Zealot's Oath?

No. That's Energy Shield Recovery, not Life Recovery.

Does Life Recovery Rate benefit The Agnostic's life restoration? And if it does, does it affect the mana sacrificed?

The Life Recovery is affected. The loss of mana is not.

What level are totems/minions/etc? I know it's based on gem level, but is there a table or something to consult? Like gem level 21 = level 75 totem, or something like that?

In general, they have a level matching the level requirement of the skill or support effect that creates them.

Does armour apply to physical damage over time like bleed?

No.

How about physical damage reduction?

Yes.

Does the "20% of Melee Physical Damage taken reflected to Attacker" mod from Basalt flasks reflect damage before or after player damage mitigation?

"Damage Taken" is inherently post-mitigation.

Are the Aegis Aurora unique mod "Replenishes Energy Shield by 2% of Armour when you Block" and rare shield mod "Recover x% of Life/Mana/ES when you Block" affected by the "Less Recovery" map mod?

No. The map mod gives less recovery rate, and these are instant recovery which has no rate to modify.

If you have the Ancient Skull Shield equipped with Necromantic Aegis while using the spectral tacticians specters and you have a way to grant the tacticians power charges, will the shield buff the SRS that they summon?

No, because Ancient Skull is a helmet, not a shield, so the minions do not gain the bonus from it.

Was the lack of a curse tag for Bane and its interaction with Vixen's Entrapment intentional?

Bane is fundamentally not a curse (and never has been). Previously, it was still considered a curse skill (had the tag) because tags are used to indicate what mechanics a skill interacts with, not just what they are. This is also why Dark Pact or the Offerings are Minion skills, despite not creating minions. This caused it to have an unintended interaction with Vixen's Entrapment, which affects socketed curse skills because it was intended to interact with actual curses, but the same tag was used for both cases. This conflicting meaning of skills having the curse tag also caused other issues with designing content, and thus is something we wanted to fix when we had a good solution. When curses were reworked, we had to distinguish between hexes and marks, which meant we now had more tags to work with and could be more specific about what each one meant - limiting the curse tag only to the skills that actually are curses, rather than just interacting with them, and applying the hex/mark tags for skills that interact with hex curses or mark curses as a mechanic. It's quite possible something similar will have to eventually happen with the minion tag to separate skills tagged as creating minions from those tagged as interacting with minions in some form.

What is the interaction with Ball Lightning and Anomalous Faster Projectiles? Is the ball not counting as a projectile? Currently the Balls do not return.

The support only gives a chance to return "from final Target". Ball Lightning never collides with any targets, so never meets this condition.

Is there a reason that damage done by the players goes through conversions one by one, but when players take damage it's all handled simultaneously regardless of the number of conversions?

All conversion (not just damage) happens in an "order" (subsequent conversions can apply to already-converted values), that's fundamental to the conversion mechanic. "Damage taken as" are not conversion, which is why they explicitly do not use that term and are described quite differently from actual conversion. That's an entirely different mechanic with different goals doing a different thing.

I think "Choose a random element" is a bit tricky to understand. Let's say I play Elemental Hit with Story of the Vaal weapon. Will they work together and pick the same element? If Elemental Hit choses Fire and the weapon choses Cold, what damage comes out? And will this hit, whatever it is, inflict freeze, shock and ignite as stated by the weapon?

Those are fundamentally different choices that happen at different times. Elemental Hit choses an element each time you attack, and that same choice is used for all damage from that attack (which could hit any number of enemies). The weapon converts damage at random, which inherently happens for each hit (because that's when damage is evaluated).

Elemental Hit cannot deal any damage of a type other than what it chose, so if for a given hit with the weapon, it converts damage to a different element than the one chosen for the attack, that damage cannot be dealt.

The hit will freeze, shock and ignite if it deals enough damage of types that can inflict that ailment to meet the minimum requirement. By default, only lightning damage contributes to shock, so a hit with no lightning damage would generate a shock with no magnitude, which is ignored. But there are modifiers which allow other damage types to contribute to ailments. 

Does Gladiator's "Blood in the Eyes" and Flesh and Stone supported by Maim support stack? Will it result in enemies I stand next to taking 40% increased Physical Damage?

Yes

Suppose you have an animated guardian wielding Sign of the Sin eater standing nearby you, and you get hit by a damage that would cause shock or chill. Whose max life pool would it use to calculate the magnitude of the effect of chill/shock?

The animated guardian's.

Do elemental ailments work if you one hit a mob? I tried out Cremator Cluster Node and realized many enemies didn't get destroyed even though I only had fire damage and high critical chance.

The Ignite is effectively simultaneous with the death - it will die and be ignited, but to be destroyed by Cremator it would need to be ignited before the hit that killed it.

Does your Animated Guardian get Avatar of Fire if equiped with Vulconus?

Yes.

Why does Shaper of Winter not Chill yourself from the 100 Fire Damage Taken if you use Eye of Innocence and ignite an enemy? What specifically is the source of the 100 Damage, is it not you? Shaper of Winter does not even specify "your hits", it just says that "All" Damage with Hits can chill.

Effects on you that cause damage to you don't have any specific source and are not modified by your damage stats - if there were, all your increased/more damage modifiers would also apply.

Does the Corrosive Elements Notable granted by Cluster Jewels work with skills that are granted or triggered by items?

Yes.

Does "Life Recovery Rate" only affect methods that recover life over time, such as life regeneration, and not ones that recover life instantly, like Escalation? Does increased life recovery rate also increase the amount of life recovered by such instant means of recovery?

Instant recovery effects do not have a rate to modify.

How does Berserker's "Defy Pain" work? The 10-stack damage is reduced by armour and physical reduction (i.e. endurance charges), but is it reduced by Reduced Reflect Damage Taken modifiers?

It is reflected damage that you are taking, yes.

Are there ways to increase the damage it deals?

You can increase how much damage you take from it with damage taken modifiers, such as being shocked. The amount of damage it tries to deal is fixed.

Regarding the Crest of Desire unique helmet's "Socketed Gems deal Double Damage", does it alter the damage * 2.0, or does it apply a "double damage" modifier? Also, does the Gladiator's ascendancy node "Painforged" multiply the damage by * 2.0, or grant a double damage modifier? In this case, how does it affect ailments like bleed and poison?

"Double Damage" is a specific mechanic. All sources of "double damage" are the same. Double Damage only affects hits, and damage can only be doubled once.

The Juggernaut node Unbreakable says 1.5% of Total Physical Damage prevented from Hits in the past 10 seconds is Regenerated as Life per second. Petrified Blood *prevents* a certain % of life loss below half life. Does physical damage *prevented* via Petrified Blood count towards the regeneration from Unbreakable?

Petrified Blood does not prevent any damage. It prevents losing life.

Why don't modifiers to chaos damage affect ignites inflicted with the Blackflame unique ring? Modifiers to fire affect fire DOT, so it would make sense for chaos modifiers to effect a chaos ignite.

Blackflame does not cause ignites to deal chaos damage. It causes enemies to take chaos damage from ignites. The ignite itself is still fire damage, the enemy changes how it takes that damage.

How does the Maw of Mischief Helmet skill "Death Wish" prioritize the minions that will be chosen first to explode? Making it choose minions based on proximity of the location of the mouse would make sense, but it seems to be almost random.

The only prioritisation it has is that it cannot affect immortal minions or minions already affected by the skill. Beyond that it is random.

About the Soul of Arakaali major Pantheon power:
"50% increased Recovery rate of Life and Energy Shield if you've stopped taking Damage Over Time Recently"
When is a player considered to be "taking damage over time"?

While the amount of damage per second they are taking is greater than zero.

If a player's regen outpaces the damage, are you still considered to be "taking damage over time"? What about leech, ES recharge, recovery from flasks etc.?

Gaining life has no impact on whether you are taking damage. If you are taking damage you are taking damage, regardless of what else is happening.

Is the "stopped taking damage" part considered as "stopped taking damage, from a source" or "stopped taking damage, from any source."?

You stop taking damage over time when you change from taking damage over time to not taking damage over time.

For example: If I am taking damage over time from two sources, let's say, an ignite from a monster, and a Caustic ground effect. If I remove the ignite (with say, a flask with the "of dousing" affix), but I remain in the Caustic Ground effect. Am I considered to have "stopped taking DoT" for starting this pantheon effect?

No. You were taking damage over time from two sources, you are now taking damage over time from one source. If you are taking damage over time, then you have not stopped taking damage over time.

Additionally, the Petrified Blood skill is worded as "life loss prevented this way is lost over 4 seconds". I assume this does not count as "damage over time", and as such, cannot ever start the pantheon effect?

Correct. Losing life is not damage. Damage can cause you to lose life (but will not necessarily do so). They are not the same thing.

Does Cooldown recovery rate affect Primal Aegis?

Primal Aegis does not have a cooldown, and I am not aware of any way to give it one that players can currently access. If it did gain a cooldown, then this would modify the cooldown, which would apply when the skill is triggered by taking the node, and prevent it being triggered again until it ran out. Since this would result in having the node allocated without the skill active (if you respecced and reapplied the passive skill fast enough), it's unlikely we'll ever add anything that can apply a cooldown to Primal Aegis.

How does elemental penetration interact with overcapped max resistance? For example, I manage to stack a total of 95% max cold res on my character. Since there is a 90% cap on max res it will display as 90% in my character sheet and I will take damage as if I had 90%?

No. Because there is a cap on maximum cold resistance, you actually do have 90% maximum cold resistance. There is no "as if you had" involved. Your maximum cold resistance cannot be raised above 90%, so 90% is the value it actually has. You just have an additional +5% to maximum cold resistance that's doing nothing, because it can't make the value bigger.

Now I do know that if this character enters a map with -10% max res that this will be deducted from my "hidden" overcap and leave me at 85% max res instead of 80%.

No. Modifiers which subtract from maximum resistance values are not any different from those which add to them - they are in fact the same modifiers, with different (negative) values.

Just like your "total of 95%" is not a single modifier but a lot of smaller modifiers to a value, the modifier applied by the map applies to the same value. Your base maximum cold resistance is 75%. You have some number of modifiers that change this value - the one from the map is one of them. The final value of the modifier is capped.

For a specific example, say your modifiers to maximum cold resistance outside the map were +10%, +5%, and +5%. These total +20%, which is added to the base of 75%, but fails to raise it above 90%, resulting in the value being 90%. Once you enter the map, you gain a new modifier of -10% to maximum cold resistance. Your modifiers to maximum cold resistance are now +10%, +5%, +5% and -10%, which results in a total of +10%, which is applied to the base of 75% and results in a total of 85% maximum cold resistance. The 90% cap isn't doing anything any more, because you're no longer trying to raise the value above 90%.

But my question is: Does it work the same way if I fight an enemy with elemental penetration?

Elemental Penetration has no interaction at all with maximum resistance, only with resistance, which is a different value. Just like maximum resistance cannot be raised above 90%, resistance cannot be raised above maximum resistance. But Penetration only cares about resistance. It doesn't look at maximum resistance at all.

Example: I get hit by a ball from the Shaper that has 25% penetration on the skill. Do I take damage as if I had 95%-25%=70% resistance or 90%-25%=65% resistance?

You technically haven't provided enough information to answer this, because you've only told me how much maximum resistance you have, not how much resistance you have.

From the numbers you gave at the start, your maximum cold resistance, as previously noted, is 90%. This means your cold resistance cannot be higher than 90%.

Base Cold Resistance is zero. If we assume that your total modifiers to cold resistance (which includes any negative ones from Kitava or things like curses) total at least +90%, then the value of your cold resistance is 90% (because it cannot be higher).

Penetration means your resistance is treated as lower than its actual value for a specific hit. If this hit penetrates 25% cold resistance, then your cold resistance against that hit is treated as 25 lower than its actual value. Since the actual value of your cold resistance is 90%, it is treated as 65% against this hit.

And as an addon to this: Is there a hidden "max" max res - or in other words a limit of how high I can overcap?

There is no limit to the number of +max res modifiers you can get, they just stop doing anything at total +15%, because the value of maximum cold resistance cannot be raised above 90% (and the base is 75%).

Does Life Leech stop when current Life reaches maximum attainable value when using Petrified Blood?

That depends on what you mean by "maximum attainable value". Life Leech only stops when unreserved life is filled.

If you reserve less than 50% of max life, then life recovery from non-flask sources (including leech) will no longer be applied to life once you reach 50%, but life leech will not be removed - it's still there giving you recovery, you're just not doing anything with that recovery at the moment. But that isn't the maximum attainable value, because you can use flasks to raise life higher to the point you fill all unreserved life - at which point all life leech is removed.

If you reserve exactly 50% of life, then the point at which the recovery stops applying is also the point at which unreserved life is filled, so life leech will give you recovery, and you'll actually apply that recovery, up until you reach 50% of max life, and then the leech will be removed, so it doesn't matter that you also could no longer apply the recovery it gives.

If you reserve more than 50% of life, then petrified blood doesn't really affect anything at all - leech is removed when unreserved life is filled.

If I put Withering Touch Support into Arakaali's Fang, then summoned spiders will apply Wither. Question: does the Corruption notable (which increases effect of Wither) apply to this effect?

No. Your minions are not you, they do not have your passive skills.

Does Shock increase Bleeding damage?

Shock increases all damage taken by the shocked object. This includes any damage over time it is taking, such as from bleeding.