General DiscussionTwo specific questions

1st question - it removes only temporal buffs. passives and auras are not temporal, therefore not affected by diffusal's active.
ex. of temporal buffs - runes, bloodlust, repel, etc.
also, the item removes negative temporal buffs if you cast it on yourself (like, dust effect, f.e.)

2nd question - you dont get HP out of armor. HP has a linear correlation with Strength, while armor has liner correlation with Agi. hp and armor do not depend on each other.
im not sure i understood this question tho.

if you mean how the damage reduction increases with armor, then use liquid dota wiki. the correlation here is not linear (additional 3 armor when you got 0 initially means a lot, but if you already have ~50, it barely changes the dmg reduction factor).

http://wiki.teamliquid.net/dota2/Diffusal_Blade
http://wiki.teamliquid.net/dota2/Armor

The damage reduction percentage seems to get lower for each armor point later on, but in truth, every single point of armor gives you %6 more resistance against physical damage.

ye seems like you are right
i think it used to be calculated differently back in the old days tho

1. Diffusial will remove buffs such as Berserk from Mask of Madness, Bloodlust from Ogre Magi and Ethereal form from Ghost Scepter. It will not remove auras such as AC aura or permanent buffs such as Flesh Heap. Furthermore, Purge from Diffusial can be used to remove debuffs such as slows and silences.

2. Every point in armor gives a 6% increase of effective HP against physical damage. Meaning that a hero with 2000 HP and 10 armor can tank 3200 physical damage before dying. This is calculated by an arbitrary formula of Dota armor law which goes:

Damage multiplier = 1-0.06*armor/(1+(0.06*armor))

Damage multiplier is a value by which incoming physical damage is increased or decreased, meaning that formula works for both positive and negative armor.

In the example of 10 armor hero I gave, DM would be:

1-0.06*10/(1+(0.06*10))=

1-0.6/(1+0.6)=

1-0.6/1.6=

1-0.375=

0.625

Which means that all incoming physical damage is reduced by 62.5%.

Effective HP is calculated by dividing actual HP with damage multiplier.

EHP = HP/DM

In above example that would be 2000/0.625 resulting in a 3200 EHP.

Remember that armor doesn't do anything versus pure and magical damage and that isn't very useful without relatively large HP. When deciding how much armor do you need in game, you are better off using your game sense than mathematics. Versus heroes such as PA, TA, Lycan, WK, Naix, Juggernaut, etc. armor is incredibly useful.

There's almost always exceptions to every dota rule. I suggest you check a wiki or online for specific buffs or debuffs that can be dispelled. For example you can remove bounty hunter's track but not viper's viper strike ult.

And omniknight's repel is an even weirder one. It's magic immunity so magical dispels don't work on it like invokers tornado. But diffusal can. Diffusal is the exception to the rule here. And like doom's ult doom, applies a dispel on cast and goes through immunity so I'd assume it removes repel as well.

http://dota2.gamepedia.com/Dispel/Removable_buffs
http://dota2.gamepedia.com/Dispel#Sources_of_dispel

Great information and some new resources to check into. Thank you guys