Damage taken as

Damage taken as is a mechanic that allows damage from one damage type to be taken as another damage type.

Mechanics

On the receiving side, damage may be taken as a different type. This is done before any sort of mitigation. It is important to note that this is not damage conversion. The shifted part of damage does not retain its original damage property so it won't get mitigated either twice or by the more favourable method. For example, if some of the incoming damage is shifted to or from physical, the after-shift value is used in the armour calculation.

Damage taken as is calculated simultaneously, this means that the incoming damage can be shifted to any other type of damage. For example The Rat Cage has #% of Fire Damage from Hits taken as Physical Damage, this modifier wouldn't have worked if it was a converted to-process.

Since damage taken as does all calculations simultaneously this also means that the initial damage can not be shifted any further.

Example

For example with Cloak of Flame and Avian Twins Talisman with #% of Fire Damage taken as Lightning Damage equipped the incoming physical damage will be shifted to fire damage but the fire damage cannot be further shifted to lightning damage. Because both of these operations would be performed simultaneously on the initial physical damage hit. So we'd be trying to take fire damage as lightning damage before any fire damage exists.

Note that damaging ailments are based on damage being dealt, not on damage taken. Changing what type damage is taken as has no effect on them. For example, when you have x% of Physical Damage from Hits taken as Fire Damage and physical damage is dealt to you, the converted fire damage never ignites you even if you have +100% chance to be Ignited. Non-damaging ailments such as shock or chill will still be applied upon converting the incoming damage to lightning and cold damage respectively.[citation needed]

This mechanic is useful against elemental penetration, especially against many boss attacks like Atziri's Flameblast (10% Fire penetration) or The Shaper's projectiles and bullet hell (25% Cold penetration), because for example if you have 50% Cold damage taken as Fire, then with a 1000 Cold hit and 75/75/75 res you would only take 500 * (1 - 0.75) + 500 * (1 - 0.75 + 0.25) = 375 damage instead of 1000 * (1 - 0.75 + 0.25) = 500 damage. If you manage to convert 100% of the penetrated element into another element then you can completely nullify the effect of penetration (in the above example, a 1000 Cold hit would be taken as a 1000 Fire hit and mitigated with 75% Fire resist, resulting in 250 final damage taken).