Basically the purpose of this guide is to explain how would any combination of items apply their bonuses on any hero.
In the World Editor of Warcraft III Units Items and Abilities are independant of each other, therefore the stacking only concerns abilities, any given Item can only have 4 abilities and one of those can be an active ability, but this problem has been solved by adding a particular ability (spellbook) that contains other abilities or by using script lines to add the ability directly to the hero and remove it when he drops the item.

Independent Stacking:

• +Damage
• +Atributes (Strength/Agility/Intelligence)
• +Mana/Life (static amount)
• +HP or MP regeneration
• +Attack Speed
• +Armor
• Cleave %
• Bash from MKB (Melee)

The skills listed above will not affect each other at all.

Examples:

1. Two Helms of Iron Will (+5 armor +3hp/sec each) will grant you +10 Armor and 6 hp regeneration per second
2. Two Quarterstaffs (+10 damage +10 Attack Speed) will give you +20 damage and +20 Attack Speed
3. One Soul Booster (+450HP +400 Mana +100%Mana Regen +4HP/sec) and one Refresher Orb (+5Hp/sec +200%Mana regen +40Damage) Results in +450HP +400 Mana +300% Mana Regen +9HP/sec and +40Damage
4. Two Battlefuries (Each gives 150% Mana Regen 6 HP/sec +65 Damage and 35% Cleave Attack) will give you 300% Mana Regen, 12HP/sec +130 Damage and 35% Cleave affecting two times the same area (If we used the term 70% here it would indicate that only one instance of damage is dealt, while in reality they are independant)
5. Two MKBs on a melee hero will give you a total of 57.75% chance to get at least one bash and a 12.25% to get a double bash dealing twice the damage but using only the longest stun duration

Check the HP and MP guide for formulas here.

Bloodstone:Stacking:

• HP Regeneration/Respawn Time/Gold Lost from Bloodstone

Will only work for the Bloodstone on the highest priority slot

Highest Priority/Bonuses Overrides Stacking:

• Evasion
• Movement Speed Bonus (Except that from Euls)
• Bash from Basher

Will not work with other abilities that grant the same bonuses, only the one with the highest bonus (or the one in the highest priority slot for Basher) will work

Examples:

1. Two Butterflies will grant you a total of 30% Evasion
2. One Butterfly and one Talisman of Evasion will grant you a total of 30% Evasion
3. Two pairs of BoT will only give you +95 MS
4. One pair of BoT, one pair of Phase Boots and 2 Eul's will grant you +120 MS
5. 6 Bashers will only grant you 25% Bash (Melee) or 10% Ranged

Movement Speed Formula
(Base Movement Speed + Flat MS Bonus) * (1 + Sum of % affecting MS)
Where:
Base Movement Speed: Is the starting MS of any hero .
Flat MS Bonus: Is the Movespeed Bonus from any kind of Boots (Only the one that provides more MS will work) + the bonus MS from Euls
Sum of % affecting MS: Is the addition of any % incresing or decreasing buffs.

Example

Darkterror (300 Base MS) with Boots, Eul's and under the effect of Degen Aura Lvl 4 (28% slow) and Empowering Haste Level 1 (6% MS increase)
TotalMS= (300+55+25)*(1-0.28+0.06)
TotalMS=296.4

Chance Stacking:

• Critical Strike
• Bash from MKB (ranged)
• Damage Block

Will not work in the same attack, they are checked in reverse order of acquisition if they proc at the same time, so only the last acquired will work.

Examples:

1. You bought a Crystalis (20% x1.75 Crit), then you acquired a Buriza (25% x2.5 Crit): You now have a 40% chance to crit from at least one of those items, and in the case both triggered (5% chance) you would only get the critical from Buriza since you picked it last.
2. You have 3 MKBs on a ranged hero: you now have 72.5375% chance to bash the enemy at least once, but in the case 2 trigger at the same time or three trigger at the same time (4.2875%) you will only get one bash.
3. You have a Vanguard and then get a Stout Shield (on a melee hero): Since you got the Stout Shield last you have a 60% chance to block 20 damage, a 28% chance to take 40 less damage and 12% chance to take normal damage.

Latest Acquired Stacking:

• Spell Resistance from Planeswalker's Cloak, Hood of Defiance or Pipe of Insight

Only the latest acquired will work

Aura Stacking:

• Vampiric Aura (Vladmir's Offering)
• Healing Ward Aura (Heart of Tarrasque)
• Brilliance Aura (Ring Of Basilius, Vladmir's Offering)
• Command Aura (Vladmir's Offering)
• Devotion Aura (Vladmir's Offering, Ring of Basilius, Assault Cuirass)
• Endurance Aura (Yasha, Sange and Yasha, Manta Style)
• Unholy Aura (Headress of Rejuvenation)
• Unholy Aura (Mekansm)
• Endurance Aura (Shiva's)
• Endurance Aura (Ancient Janggo of Endurance)

Auras will not stack with themselves because they place a buff on the affected units, and since the units can't acquire the same buff two times they will only be affected by the aura with the highest value.
The aforementioned auras will work with any of those in a different line.
Example:

1. A unit under the effect of a Vladmir's Offering's Auras with a Basilius will use the Brilliance/Devotion Aura from Vladmir's plus the Vampiric and Command Aura.

Orb Effect Stacking:

• Corruption (Stygian Desolator)
• Chain Lightning (Maelstrom, Mjollnir)
• Feedback (Diffusal Blade)
• Lifesteal (Mask of Death, Mask of Madness, Helm of the Dominator, Satanic)
• Item Attack Frost Bonus/Frost Attack (Eye of Skadi)

Any attack can only have one Orb Effect and One Buff Placer, The rules to distinguish which is applied will be seen here.


XX: Notes

Item Priority in Slots order
1 2
3 4
5 6

Caps

• Attack Speed is capped at 400 and -80
• Movement Speed is capped at 522 and 100 (Note that some skills like Ensnare are hardcoded to set MS to 0)