Esta guia es muy util ya que explica el tipo de daño de todos los spells y que es lo que los reduce.
Why should we care about triggered damage?
There are many differences between triggered damage and the usual spell damage, but the one that is worth our attention to we normal game players is that triggered damage is calculated by two types, attack type and damage type.
What is attack type?
Attack type is the usual "hero damage", "piercing attack" we're talking about. They can be found easily by clicking any unit, and pointing your mouse cursor on the damage and armor icons.
Attack type uses all forms of attacks: Hero, Normal, Piercing, Siege, Spells and more. The reduction/increase of this damage is calculated by the opposing armor type. For example, Siege attack deals extra damage to Fortified armor. The only exception to this is Spells. Spells will be reduced by the spell resistance of the target. More information can be found in the FAQ of Attack Type and Armor Type.
What is damage type?
On the other hand, damage type is something that is "under the scene". There is no easy way you can tell the damage type of any particular spell unless you really test it thoroughly or you have access to the map information.
There are many Damage types, but they can be grouped into three classes: Physical, Magical and Universal. There are two main types of damage used in triggers: Normal and Magic. Normal is physical damage and magic is magical damage. The opposing amount of armor will reduce the damage done if it's normal damage, but armor will not reduce magic damage. Also note that normal damage is also considered as some sort of melee attack. It will trigger Frost Armor, Blade Mail and more.
Subtle difference between damage type and attack type when applying magic immunity:
Magic Immunity will prevent any damage done by skills that use the magical damage type, but will not stop any damage done by the spells attack type.
Detailed list of damage type and attack type of triggered spells:
The following list will provide you with information on which skills use which type of damage and attack. I've noted which of these are reduced by armor type, armor quantity and/or spell resistance. Any skill not mentioned here is considered Spells Attack and Magic Damage (Reduced only by spell resistance).
Normal Attack, Normal Damage (Reduced by armor type and armor quantity)
Spells under this category are more or less like a normal physical attack. Magic resistance is irrelevant to these spells, and the only factors that affect the damage is a unit's armor type and armor. For more information on armor type please click here
Chaos Attack, Normal Damage (Only reduced by armor quantity)
Similar to above, magic resistance is irrelevant. Further, Chaos attack deals 100% damage to all kind of armor types, so the only factor that affects the damage is a unit's armor.
Piercing Attack, Normal Damage (Reduced by armor type and armor quantity)
Same as above except that the attack type is Piercing, meaning it deals 150% damage to unarmored units e.g. enemy creeps, 50% damage to heroes, and 35% to buildings. This explains why Scattershot is very useful against clearing creeps.
Hero Attack, Normal Damage (Reduced by armor type and armor quantity)
Basically this is exactly the same as the hero's physical attack.
Backstab (SA images don't do backstab damage)
Counter Helix (Axe images deal full damage for counter helix)
Enrage (Note that while Ursa is a ranged hero, Enrage is a melee attack).
Note on penitence: Penitence's damage is calculated as follows: suppose a unit is under penitence and is being Dagoned. Dagon deals 400 damage, after magic resistance is 300. In addition, Penitence deals an additional 28% damage (which means 112 HP). If the hero'es armor reduction is 50%, then the additional damage dealt by Penitence is 56HP.
Hero Attack, Magical Damage (Only reduced by armor type)
These spells are your favorite! The words "magical damage" means that armor is irrevelant in calculating damage, and the words "hero attack" means that hero magic resistance doesn't reduce damage of these spells. In other words, these spells deal exactly the damage as stated.
Glaives of Wisdom
Impetus (Maximum damage of Impetus is 400)
Test of Faith
Notes on Gravekeeper's Cloak:
This passive works in that whenever the hero is damaged, no matter what the source and even if he is killed, all units within 400 area of effect with the Gravekeeper's Cloak buff will take the listed amount of damage.
This passive does not work when over 1400 damage is done to the hero at once. This is to prevent a spell such as Axe's ultimate, which deals a huge amount of damage when its target is under the amount of life listed, from obliterating all nearby units.
This passive also reduces the damage done to the Visage whether or not any units are around, although, because it works much like the Bristleback's passive, it does not prevent lethal damage.
Spells Attack, Normal Damage (Reduced by spell resistance and armor quantity)
These spells are "bad" in the sense that both magic resistance and armor will reduce the damage dealt, which means these spells will almost do nothing to an Anti-mage with 30 armor .
Lvl? Death (Only the bonus damage is affected by armor, the regular damage, of course, belongs to spell attack type and magic damage type).
Nether Strike (Only the bonus damage is affected by armor, the accompanying Greater Bash doesn't belong to this category).
Spirit Bear (This is the damage that Syllabear will receive when the Spirit Bear is dead, which means it almost does nothing to him late game when his Spirit Bear dies. However, when the Spirit Bear is dead, Syllabear will lose 1/1.3~/2/4% of his total experience).
Spells Attack, Magical Damage (Reduced only by spell resistance)
These triggered damage spells are just the same as most other spells in terms of damage dealt to opponents.
Other triggered spells
The following are spells that do not fall into any of the above categories, they are discussed on a case by case basis.
Toss: Toss is only reduced by spell resistance, and deals half damage to buildings.
Greater Bash Greater Bash is only reduced by spell resistance. Each upgrade means an additional 0.3 stun duration.
Meat Hook: Meathook is only reduced by spell resistance.
Laser: As the tooltip explicitly says, it always does exactly the damage it deals.
How do I apply the above knowledge into my DotA experience?
The following examples are written to help you ensure that you have grasped the main concepts of triggered damage. If you don't understand how the final damage is arrived, you'd better review the concepts again.
I cast a 400 damage Test of Faith on a hero. Since Test of Faith is not reduced by either spell resistance or armor quantity and hero attack is not reduced by hero armor, it will deal a full 400 damage to that hero.
I cast a scattershot on a hero with 15% damage reduction because of armor. 10 sharpnels hit the target and deal 20 damage each, meaning a total of 200 damage. Piercing attack does only 50% damage to hero armor and it will also be reduced by another 15% because of the armor quantity. Scattershot will now deal 200*0.85*0.5 = 85 damage on the target hero