Damage Manipulation

Besides armor and magic resistance, there are some other ways manipulate damage, ranging from amplifying damage, reducing damage and even blocking damage completely.

Mechanics
Only the 3 damage types, physical, magical and pure damage can be subject to damage manipulation. Usually, all spells using this mechanic amplify, reduce or block all 3 damage types, however, some of them only affect 1 or 2 damage types. HP removal cannot be manipulated.

Stacking
All sources of damage amplification stack additively. This means a unit affected by 2 different sources of 50% damage amplification, it will take 100% more damage.

The stacking rules for damage reduction varies. Some of them stack multiplicatively, some additively and some don't stack at all.

Damage amplification
Damage amplification causes afflicted units to take additional damage. Damage amplification usually increases incoming damage directly in the same damage instance.


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Damage reduction
Just like how damage can be amplified, it can also be reduced. Some of these also have extra effect based on the reduced damage. Because of this extra effects, there are certain priorities. However, most of the percentage-based damage reduction abilities stack additively, meaning it is possible to reach 100% damage reduction.


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Damage negation
Damage negation causes entire instances of damage to deal no damage to its target, however, the instance is still registered by the game. This means, when something reacts on damage without having a minimum damage threshold, it will still react on the negated damage.


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Preventing on-damage effects
Many abilities react on damage a unit receives. In some cases, fully negating the damage causes them to not proc. However some on-damage effects also react on 0 damage so they still may proc even when the proccing damage got negated.

The following abilities and effects do not react on damage when it gets fully negated.

1 Includes all sources of lifesteal, except, and 's Spell Lifesteal.

2 These work when the damage gets negated by.

3 These abilities have damage counters, which do not work when the damage gets negated.

4 's "pseodo-heal" mechanic described earlier damage does not work when the damage gets properly negated, otherwise it would cause units to get healed.

5 does not reduce damage at all when under the effect of any damage negation or reduction besides magic resistance and armor. Despite this, it still loses charges when under the effect of, without blocking damage.

The following abilities still do react on fully negated damage.

1 The damage of and the damage spread of  are fully unaffected by any form of reduction, except for magic resistance and armor.

Pre-Heal
Pre-Heal, just like regular damage negation, prevents a unit from dying. However, the way in which that is achieved is completely different. Instead of directly reducing or negating damage, this mechanic rather manipulates the health of the unit.

A Pre-Heal, only activates when the unit is going to receive a damage instance which exceeds its current health. If that happens, the unit's current health gets increased equal to the amount of the incoming damage plus one, right before the damage hits. This causes the unit's health to land exactly at 1. This also works when an incoming damage instance is greater than the unit's maximum health. In this case, its maximum health gets increased as well and immediatly reverted to default after the damage hits.

This means that technically, the incoming damage is not reduced at all. This is the reason why the abilities which use this mechanic do not prevent any on-damage effects from triggering, unlike regular damage negation. This mechanic also has a great synergy with 's Damage Return: When for example a hero at 1 health takes 1000 damage, Blade Mail usually would reflect 1 damage. But when combined with a pre-heal, it reflects the full 1000 instead, since the hero technically takes 1000 damage due to the pre-heal effect.

The following abilities use this pre-heal mechanic

Armor & Magic Resistance
Unlike the sources of other damage manipulation, armor and magic resistance are traits every unit has in the game by default, although there also are abilities which are able to change a unit's armor or magic resistance value.

A unit's armor only interacts with physical damage, increasing or decreasing the damage based on the armor value.

A unit's magic resistance only interacts with magical damage, also increasing or decreasing the damage based on the magic resistance value.

There is no equivalent trait like this for pure damage.