Something I've discovered we all argue about, be it newer players to the game or some more regular Dota addicts, is the mechanics of the game. Do certain passives stack? If I build this can I still use this? Will he be able to attack me if I activate this at the right time? What about spells? Mechanics, though important to the game tend to trip us up a bit. So with this guide I'm looking to help explain the mechanics to passive stacking with items.

Evasion: Now this is a more common argument. First off I'll start by saying Evasion does NOT stack. It always takes the highest percent Evasion you have and uses that one. However, there are some exceptions to that such as Faceless Void's Backtrack ability.

Faceless Void dodges damage by jumping backward in time, eluding both physical and magical attacks.
Dodge Chance: 10%/15%/20%/25%

Now let's say you grab a Butterfly on Faceless Void as well. Giving you the extra 35% Evasion from that.

Dodge Chance: 35%

Faceless Void's Backtrack is not considered as Evasion. All total this gives you a 51% chance to dodge all physical attacks (due to diminishing returns which I'll explain later in the article I promise) and 25% chance to dodge spells off Backtrack. Monkey King Bar is one well known counter to Evasion as well since it grants the hero the ability to never miss attacks. It's worth noting here that Monkey King Bar will not work on Faceless Void's Backtrack since it's technically a triggered heal and not a “dodge”.

Block and Crit Chance: This mechanic works roughly the same way as Evasion does since it's chance based and works with diminishing returns. Meaning for example that let's say you grab a Vanguard and then pick up a Stout Shield, your last picked up, not bought item will have the priority. Meaning your Stout Shield was picked up last and has the priority. So you gain the 60% block chance of the Stout Shield and then the Vanguard you grabbed earlier has the diminishing return block chance of 28%. This gives you a grand total of 88% chance to block damage. Please note this isn't an 88% chance that both will proc since that is impossible.

Let's say your 60% chance to block with Stout Shield procs, than followed by the 28% chance of Vanguard also procs. The highest block will take effect, meaning Vanguard will be the one to actually take effect. The same rule for block chance also applies to all other passives as well.

Diminishing Returns: As promise I will explain how diminishing returns work and the math involved. Now it's important to note there is different formulas depending on what you're trying to find diminishing returns. Since this guide covered item passive stacking, I'll cover the formulas for that.

-Diminishing Returns on Passive Abilities:

Now the trick to figuring this out is to first find what is the chance one of your passives will fail. So let's look at the Stout Shield and Vanguard for this example. Stout Shield has a 60% chance to block which is a 40% (.4) chance it will fail. Now let's say before you grabbed you Stout Shield, that you had a Vanguard. Which is a 70% chance to block something, meaning it has a 30% (.3) chance to fail at blocking. Now to figure out the chance of both getting the block you use this forumla.

100% - (chance of first item to fail)*(chance of second item to fail)

So let's input our numbers we got into the forumla shown

100% - (.4) * (.3) = .88 or 88%

So above we took the( fail chance of the Stout Shield ) * ( fail chance of the Vanguard ) and then subtracted that from 100% or 1. This gave us an 88% chance for both to activate. Now to figure out the chance of each one seperately you have to remember which one you picked up last. In this example we picked up the Stout Shield last, which gives that item the full value. Meaning Stout Shield still has a 60% chance to block. You then subtract that number from the chance of both activating ( 88%-60% = 28% ) that leaves the Vanguard with only a 28% chance of activating.

This formula is used to figure out all passive stackings. Be it abilities on characters or items. So next you and your buddies are getting into arguments about if it's better to stack passives, such as getting crit items on Skeleton King or a item with bash on Facless Void, you'll be able to bust out this formula and figure it out exactly. Hopefully this guide has helped some of you get a better understanding of stacking passives within Dota 2. As always feel free to post comments on what you like, didn't like, or any questions you have!