Originally posted by Malice on PoE forums- below is an in depth, simple to understand summary of the PoE mechanics.
There are three difficulty levels: Normal, Cruel, and Merciless. You must complete Normal difficulty before you can move to Cruel, and you must complete Cruel before you can move to Merciless. The higher difficulties have death penalties, causing you to lose experience when you die. They are 0% for Normal (no penalty), 7.5% for Cruel and 15% for Merciless difficulty. This is a percentage of the experience needed to gain the next level, not your total experience.
Losing experience in this way cannot cause you to drop down a level. For instance if you have 11% progress to your next level and die in merciless difficulty, your progress will be reset to 0%. There are also penalties to resistances in higher difficulty levels. In Cruel difficulty, there is a -20% penalty to player resistances, and this increases to -60% in Merciless.
Skills currently come in two main varieties: spells, and attack skills. Any skill that uses your weapon damage counts as an attack skill, and everything else counts as a spell.
Attack skills are dependent on your weapon, and so are affected by attack speed, accuracy, etc.. Bonus damage from rings and other gear is applied when using an attack skill.
Spells do not draw their damage from your weapon in any way. They are affected by % cast speed, %fire/cold/lightning damage, %spell damage, and critical strikes. Integer damage bonuses on gear are not added to spells.
Traps are very similar to spells, but are not affected by cast speed or spell damage mods. They are affected by % trap laying speed, and relevant damage mods. Integer damage bonuses on gear are not added to trap damage.
The only exception to this is Town Portal, which is not affected by attack speed, cast speed, or anything else.
Support gems only affects skills where it makes sense. For instance, skills that do not already do damage (such asTemporal Chains) will not benefit from Added Cold Damage. Skills that do not already have an area of effect will not benefit from Increased Area of Effect, etc.
Skill gem experience gain
Gems get experience equal to 10% of the experience you earn.
The number of gems you have equipped has no effect on the rate of XP gain. So having less gems equipped does not cause them to gain XP faster than if you had many gems equipped.
Gems are not affected by the experience penalty when facing enemies below your level.
Gems do not lose experience when you die.
Flasks come in four main varieties: life flasks, mana flasks, hybrid flasks, and utility flasks.
Life, Mana, and Hybrid flasks
These flasks cause you to regenerate life and/or mana when used. The amount recovered is shown on the flask as Life Recovery and Mana Recovery. The time it takes to recover the full amount is shown on the flask as Recovery Time. If you reach your maximum life and/or mana amount before the end of the recovery time, the flask effect will end prematurely. For example:
You are at 100/300 life, and 150/200 mana. You use a hybrid flask that has 400 Life Recovery, 200 Mana Recovery, and Recovery Time of 8 seconds. After 2 seconds, you will be at 200/300 life, and 200/200 mana, and the mana recovery effects ends. The life recovery continues, and at 4 seconds, you have reached maximum life, and the life recovery effect also ends.
Flasks can have magic modifiers that provide bonuses while the flask effect is active, for example increased movement speed or resistances. These bonuses end when the life/mana recovery effect ends.
When multiple flasks are used at the same time, the effects are queued. The effect with the highest regeneration rate is always applied first. For example:
You have two flasks, one that gives 500 life recovery over 10 seconds and has a 20% increased movement speed modifier, and a second that gives 500 life recovery of 5 seconds with no additional modifiers. You use the first flask and gain the movement speed while recovering life. After one second, you use the second flask. At this point the remaining 9 seconds from the first flask is queued, and the second flask begins its effect. Once the second flask has expired, the first flask resumes its effect for the remaining duration.
These flasks give a temporary bonus for a set duration. Unlike the other flasks, the effects are not queued, each effect has its own timer that can overlap with other effects. The default effects of the flasks will not stack. For example:
You have a magic Granite Flask with +25% movement speed, and a regular Granite Flask, both giving +4000 armour for 4 seconds. You drink the first flask, and one second later you drink the second second flask. The result will be that for the first four seconds you will have +4000 armour and +25% movement speed. At the four second mark the first flask ends, but the second flask still has 1 second left. So you will have +4000 armour (but not the movement speed) for another 1 second.
Drinking a flask consumes flask charges. Each flask shows how many charges are used per drink in its description, and each flask has a maximum number of charges it can hold. Whenever you or one of your minions kills an enemy, all of your flasks gain charges.
By default regular monsters grant 1 charge each, magic (blue) monsters grant 3.5 charges each, and rare (yellow) monsters grant 6 charges each.
So killing a rare monster causes all of your flasks to gain 6 charges.
The main difference between the classes is their stating location on the passive skill tree. Classes also start with different amounts of attributes at level 1:
Marauder: 30 STR, 14 DEX, 14 INT
Ranger: 14 STR, 30 DEX, 14 INT
Witch: 14 STR, 14 DEX, 30 INT
Duelist: 22 STR, 22 DEX, 14 INT
Templar: 22 STR, 14 DEX, 22 INT
Shadow: 14 STR, 22 DEX, 22 INT
Life/mana per level
All classes begin with the same base stats, and gain the same amount per level:
50 life, +6 per level
40 mana, +4 per level
50 evasion, +3 per level (including level 1)
Attributes are required to equip gear and skills. The three attributes also grant some passive bonuses:
Strength grants +0.5 life and +0.2% melee physical damage per point
Dexterity grants +2 accuracy and +0.2% evasion per point
Intelligence grants +0.5 mana and +0.2% energy shield per point
Therefore the +10 attribute passive skills effectively grant:
+10 Strength: +5 life, +2% melee physical damage
+10 Dexterity: +20 accuracy, +2% evasion
+10 Intelligence: +5 mana, +2% energy shield
Life and mana regeneration
All classes have a base mana regeneration rate of 105% of their maximum mana per minute. For example, a character with 100 maximum mana will regenerate 105 mana per minute, or 1.75 mana per second.
"Increased Mana regeneration rate" modifiers modify the base rate. For example, 20% Increased Mana regeneration rate would result in 105 * 1.2 = 126% per minute.
Characters do not begin with any life regeneration, but it is available from gear and passive skills.
The rate at which you gain life from life leech is 20% of maximum life per second. If you have 1000 maximum life, and leech 600 life with a single attack, it will take three seconds for that life to be applied to your current life. You always get the full amount of life leeched, although it may take time to be applied - if you leech a large amount of life during a battle, you may find that the life gain continues long after the battle is over. Similar to flasks, the life gain from leech will end if you reach maximum life.
The same is true for mana leech, although the rate is 12.5% of maximum mana per second.
Effect of level on experience
Level affects the amount of XP you gain from killing enemies, based on the relative level of the player and monsters. A penalty is applied if you are too far above or below the monster level.
There is a safe level range where no penalty is applied, which is equal to three, plus one for every sixteen complete player levels. Any additional level difference in excess of this safe range is called the Effective Difference.
The formula then applied is:
((PlayerLevel +5)1.5) / ((PlayerLevel+5+(EffectiveDifference2.5))1.5)
So a level 24 character has a safe band of 3+1=4 levels. So from Monster level 20 to 28, there is an effective level difference of 0. At Monster Levels 19 and 29, the Effective level difference is 1. The Effective Difference matters in either direction.
Here are graphs of the experience multiplier by monster level and by effective level. [in original source]
Dual wielding grants a +10% attack speed bonus, and a 15% chance to block. The attack speed bonus is applied multiplicatively with other attack speed modifiers.
The default attack and certain other skills will alternate between each weapon, striking with each hand in turn.
Some skills (such as Cleave and Dual Strike) attack with both weapons at once, while others only use the main-hand weapon.
Hit & damage calculation order of effects
There are a number of steps involved in deciding whether an attack hits or not and how much damage is done:
1. Avoiding the hit:
At this stage there is a chance to evade attacks (accuracy vs evasion)
Any chance to dodge from acrobatics or phase acrobatics is also checked here
2. Avoiding the damage:
Blocking is checked
3. Mitigating the damage:
Physical damage reduction and resistances are applied
4. Taking the damage:
Non-chaos damage is removed from energy shield until it's depleted.
Any remaining damage (including all chaos) is removed from life.
Whenever a player or monster takes damage, there is a chance they will be stunned. A stun interrupts whatever that creature was doing while a brief animation is played. The default length of stuns is 350ms. The duration of stuns can be altered by increased block and stun recovery, increased stun duration, and similar modifiers.
For increased block and stun recovery modifiers, the formula used is: 350 * (100 / ( 100 + increased recovery) )
The formula used for determining whether or not a stun occurs is: stun_chance = 200 * damage / defender_effective_max_life
Where defender_effective_max_life is the maximum life of the creature being hit. Increases to monster life from a party of more than one player do not affect defender_effective_max_life.
For a player with Chaos Inoculation, their defender_effective_max_life is whatever their max life would be if they did not have Chaos Inoculation.
Reduced stun threshold modifiers reduce the value of defender_effective_max_life. For example, 25% stun threshold reduction means you treat their maximum life as only 75% as much as it actually is, meaning you stun them easier.
If the stun chance would be less than or equal to 25%, it's ignored, so you need to deal more than 12.5% of effective maximum life to have a chance to stun.
Accuracy is compared to enemy evasion when determining if an attack hits or misses. The complete formula is below:
chance to hit = attacker_accuracy / ( attacker_accuracy + ((defender_evasion/4)0.8))
Chance to hit can never be lower than 5%, nor higher than 95%.
Evading an attack prevents all damage and other harmful effects from the attack. Only attacks and attack skills can be evaded. Spells cannot be evaded.
Evasion also gives a chance to avoid critical strikes. If an incoming critical strike succeeds its hit roll, a second hit roll is performed to determine if the critical is evaded or not. This second roll is the same as the regular hit roll above (accuracy vs evasion). If this roll succeeds, a critical strike is scored. If it fails, the attack still hits, but only for regular damage.
Critical strikes from spells cannot be evaded.
Blocking an attack prevents all damage and other harmful effects from the attack. Usually, only attacks and attack skills can be blocked, but there are some passive skills that allow you to block spells.
Chance to block is capped at 75%.
When an attack is blocked, the game first calculates if the attack would have caused a stun were it not blocked. If it would have caused a stun, the blocking animation is played, stunning you briefly. If it would not have caused a stun, then you get a "free" block with no animation. Faster Block and Stun Recovery and Increased Block Recovery modifiers reduce the length of the blocking animation.
Armour / Damage Reduction
Damage Reduction reduces physical damage taken. Elemental damage and damage-over-time are not affected. The amount of damage reduction depends on the defender's armour total, and the attacker's attack damage:
reduction = armour / (armour + 12*damage)
The amount of reduction is capped, it cannot be more than 90%.
The fact that damage reduction scales with the amount of damage means it is difficult to know exactly how much damage is being reduced.
An easy to remember rule of thumb is that to achieve 50% damage reduction, you will need an armour rating equal to twelve times that of the damage being dealt. For example, to achieve 50% damage reduction against a 100 damage hit, you'll need 1200 armour.
As long as you have greater than 0 Energy Shield, you have a 50% chance to avoid stun.
Energy Shield acts as an additional hit point pool on top of life. If you have any Energy Shield remaining when you take damage, the damage is subtracted from the Energy Shield first. Damage is only applied to life once all Energy Shield is depleted. The exception to this is Chaos Damage, which ignores Energy Shield.
Energy Shield will recharge if you do not take any damage for a certain period of time. The default delay is 6 seconds. This time can be reduced with increased energy shield cooldown recovery modifiers from passive skills. The formula for the recharge delay is: 6 * (100 / (100 + increased recovery) ) so 100% increased recovery is halving the delay, not removing it entirely.
Whenever you use a skill or attack, you have a chance to deal a Critical Strike. Critical Strikes are rolled on a per-action basis, not per-monster.
So each time you use a skill, the Critical Strike roll is made once and only once. If you roll a Critical Strike, you will deal Critical damage to all enemies hit by the skill.
Critical Strikes do more damage than normal, based on yourCritical Strike Damage Multiplier.
All characters have a base Critical Strike multiplier of 150%, meaning a critical strike does 150% of normal damage. This multiplier can be increased with various skills and modifiers on items.
For instance, with a multiplier of 250%, if you deal a Critical Strike with attack that normally does 100 damage, you will instead deal 250 damage.
The chance to deal a critical strike is taken from the weapon used to perform an attack or attack skill, and in the case of spells, each spell has it's own critical strike chance, which is listed in the skill gem's description.
This value can be increased by increased critical strike chance modifiers from spells and gear. For example, if you are using a weapon with 5% chance to crit, and you have 50% increased critical strike chance, you will have a 7.5% chance to score a critical strike.
Critical chance can not be less than 5% nor more than 95%.
Critical Strike Chance and Critical Strike Damage Multiplier are calculated separately for each spell and weapon attack. All weapons and damage-dealing spells have a base Critical Strike chance listed on them. This only affects your chance to critical for attacks made with that weapon or spell. For instance the critical strike chance on a wand does not affect your chance to critical with a spell.
Non-spell critical strikes can be evaded. See the evasion section above for details.
There are currently 5 main types of damage, they are Physical, Fire, Cold, Lightning, and Chaos.
Fire, Cold, and Lightning are collectively known as Elemental Damage.
Damage reduction from armour only affects physical damage.
If you land a critical strike with an attack or spell that deals fire damage, the enemy begins Burning. Burning causes damage over time. Humanoids, Monkeys and Sea Witches will flee while burning. Burning lasts 4 seconds, and the amount of damage over time is 1/3 of the fire damage dealt per second. So a total of 4/3 of the original damage, over 4 seconds.
Multiple instances of burning can be applied at the same time, however the damage from them does not stack. Only the highest-damage burning effect that is on a creature at any one time will deal damage.
Hitting an enemy with cold damage can cause the enemy to be Chilled. Critical hits with cold damage can also cause the target to be Frozen. Chilled enemies move, attack, and cast 30% slower, while frozen enemies cannot do anything except drink flasks.
If you land a critical strike with an attack or spell that deals lightning damage, the enemy becomes Shocked. This can be stacked up to three times on one target. In this state, monsters or players take 40% additional damage per instance of Shock. Shock stacks additively with itself, for a maximum of 120% with a stack of three. The damage multiplier itself applies multiplicatively with your final damage, since it it increasing the damage the enemy takes, rather than the damage you deal.
Chaos damage ignores energy shield, reducing life directly.
Chaos damage is not considered to be "elemental damage".
Fire, Cold, Lightning, and Chaos damage each has its own resistance value (eg "Fire resistance") which is viewable in the character sheet. Resistances reduce damage taken (or increase damage if they are negative), and are capped at a maximum of 75% by default. This maximum can be modified by certain skills. There are penalties to resistances in higher difficulty levels. In Cruel difficulty, there is a -20% penalty to player resistances, and this increases to -60% in Merciless.
Burning, Chilled, Frozen, and Shocked are collectively known as Status Ailments.
The duration of the chilled, frozen, and shocked statuses is related to the amount of cold/lightning damage dealt:
Shocked: 276ms per 1% max life dealt as lightning
Chilled: 138ms per 1% max life dealt as cold
Frozen: 100ms per 1% max life dealt as cold
All three are capped at considering 1/3 of max life - if you deal more than 1/3 max life as that element, the status ailment occurs as though you did exactly 1/3.
The maximum unmodified durations are therefore:
Shock: 9.2 seconds
Chill: 4.6 seconds
Freeze: 3.33 seconds
If the duration would be less that 300ms, it's ignored entirely (the effect is not applied).
For characters using Chaos Inoculation, these durations are calculated based on what the character's maximum life would be if they did not have Chaos Inoculation.
Some skills grant Endurance (strength), Frenzy (dexterity), or Power (intelligence) charges.
Each charge lasts a short duration before it disappears. Gaining a charge resets the duration of all accumulated charges.
Endurance charges are related to the strength attribute and grant +5% physical damage reduction, and +5% to elemental resistances (fire, cold, and lightning) per charge.
The physical damage reduction stacks with the damage reduction from armour, so that they are both applied at the same time. For example, if a monster deals 100 damage, and you have 10% DR from two endurance charges, and enough armour to prevent 30 of the 100 damage, the incoming damage would be reduced by 40.
Frenzy charges are related to the dexterity attribute and grant +5% attack speed and +5% cast speed per charge.
Power charges are related to the intelligence attribute and grant +50% critical strike chance per charge.
By default characters can have a maximum number of 3 active charges of each type at one time. This maximum can be increased by certain passive skills.
The maximum party size is 6 players.
Effect on monsters
Monsters gain 50% extra life for each additional party member after the first. For example, against a party of 3 players, monsters have double life.
The original life amount is used for the purposes of determining the length of stuns and status ailments from elemental damage - this means monsters will not be harder to stun/ignite/etc. when fighting in a party.
Effect on loot
Each player in a party after the first gives a +50% item quantity modifier on drops. So a party of three will see twice as many drops as a lone character.
Increased Item Rarity & Quantity modifiers are only counted from the player who lands the killing blow.
See the drop rates section above for more information about item rarity and quantity bonuses.
Effect on experience
Only party members that are nearby (roughly two screens) receive experience from a slain monster. If one member is in town or too far from the monster they get no XP. Monsters are still made harder by players elsewhere on the level but outside of XP range.
Effect on flasks
Only the character landing the killing blow on an enemy will gain flask charges. The same is true for all +life and +mana gained "when you deal a killing blow" modifiers.
Flasks have a +75% charge recovery bonus for each party member after the first.
Most gear has attribute requirements that must be met in order to equip the gear. These requirements come from the base item type and are unaffected by magical modifiers, quality, or number of sockets.
Some items have a level requirement that must be met in order to equip the item.
There are two factors that affect level requirements.
The level of the base item type. This is the level that the item starts appearing (and is separate from the itemlevelthat affects which magical modifiers can spawn on it). See the item data link above for a list with all item levels. Some of the very low-level base items do not come with a level requirement.
The level of the magical modifiers. The level requirement for magical modifiers is equal to 80% of the level of the highest-level magical modifier on the item.
The highest level requirement of the two listed above is the one that appears on the item.
There is a penalty to the chance of currency items (scrolls, orbs, etc.) dropping in areas with a monster level more than two levels lower than your character level. For each additional level that you have compared to the area's monster level+2, the chance of a currency item drop is reduced by 2.5%.
So if you are level 30 in a level 20 area, you will see 20% less currency item drops on average:
A level 30 character in a level 28 area will see no penalty.
Currency item Drops are not increased or decreased in this way when fighting in areas above your level.
For the purposes of this penalty, your level is never considered to be higher than 68. Therefore a level 75 character receives no penalty in a level 66 area.
There are two modifiers that affect drop rates in the game,increased item rarity, and increased item quantity.
There are three potential sources of these modifiers:
the player (skills, passives, gear etc.)
monsters (such as bosses and champions)
Modifiers from the player stack additively with each other, and are subject to diminishing returns.
Modifiers from the party bonus and monsters stack additively with each other, and are not subject to diminishing returns.
The total player bonus stacks multiplicatively with the total party & monster bonus.
Increased Item Rarity
Increased Item Rarity % modifiers increase the chances of an item being magic, rare, or unique. For example with a total of +100% increased item rarity, you'd get twice as many magic items, twice as many rares and twice as many uniques from normal enemies.
This modifier has no effect on the number or type of currency items, scrolls, or gems that drop.
When in a party, only the modifier from the player who lands the killing blow on an enemy is counted.
If one of your minions gets a kill, the minion's IIR is added to yours and the total is used.
Magic, rare, and unique monsters have an Increased item rarity modifier for drops.
Increased Item Quantity
This modifier increases the average number of items that drop from monsters and chests. It does not affect the type, quality, or rarity of item dropped, only the chance thatsomething will drop. There is no cap on the usefulness of this modifier, as monsters can drop more than one item at a time.
The base chance for an item to drop from a normal monster is 16%. This varies between monster types, and special monsters have higher drop chances.
When in a party, each player in the party after the first gives a +50% item quantity modifier on drops.
IIQ & IIR modifiers from support gems currently do not work with kills made by damage over time effects, such as the poison from poison arrow. Modifiers from your gear will affect those kills however.
All weapons, armour, flasks and gems can randomly receive between +1% and +20% quality.
This value can be increased by Whetstones, Armour Shards,Flask Quality Upgrades, and Gem Quality Upgrades, but is capped at 20%.
The effect of quality depends on the item:
On weapons, increased physical damage
On armour, increased Armour rating, Evasion, and Energy Shield
On flasks, increased life and mana recovery
On utility flasks, increased duration
On gems, the bonus is specific to each gem. For instance,Frenzy gets increased damage, while Cleave gets increased attack speed.
On maps, increases the item quantity bonus from monsters in the map area.
Modifiers are split up in to two main groups, prefixes and suffixes. A magic item can have only one prefix and one suffix, never two prefixes or two suffixes.
Rare items can have up to six modifiers, it is unknown if there is a limit on how many of these can be prefixes/suffixes.
A randomly generated rare item (from a drop or Orb of Alchemy) receives between four and six modifiers randomly, with the following odds:
1/12 chance of 6 mods
4/12 chance of 5 mods
7/12 chance of 4 mods
All modifiers have a level associated with them, and will only appear on items whos item level is greater than or equal to the modifier's level.
Lists of available magical modifiers are available in the item data section.
The "Culling Strike" modifier (found on some unique items) causes monsters to die if you strike them down to 10% or less life.
In general, integer modifiers are applied before percentages. Percentage modifiers using the words "% increased" or "% reduced" stack additively with one another, while "% more" and "% less" modifiers stack multiplicatively.
When dealing with weapons, some modifiers that are listed on the weapon itself are applied first, before mods from other pieces of equipment, skills, and so on. This includes anything affecting physical damage, such as increased physical damage, added physical damage, quality etc., and also attack speed, critical strike chance, critical strike multiplier, and accuracy. It does not include elemental damage mods.
Similarly, when dealing with armour, evasion, and energy shield on armour, any modifiers affecting those stats that are listed on the piece of armour are applied first. This includes quality and any other mods directly affecting armour, evasion, or energy shield amount. It does not include mods affecting the energy shield recharge delay or regeneration rate, only the amount of energy shield.
Imagine I have 100 life, and two passive skills that increase total life by 15%. The total bonus will be 30%, resulting in 130 life. Now imagine I am wearing boots that give +40 life, and have a passive skill that grants +20 life. The integer bonuses are applied first, giving me 160 life, then the percentage bonuses are applied to that subtotal, for a final total of 208 life.