Abyssus question

[C0DEx]

Hey there. So I'm using Abyssus for the first time, and I'm wondering how exactly the damage is applied. I googled for a bit but only found old posts about it and I'm not sure if stuff has changed, thats why I wanted to ask.
From what I can tell there are 2 possibilities. I'll take 100 dmg as example.

1. 100 base damage, 140 base damage with applied 40% debuff. After 90% phys reduction 14 damage are left, instead of 10 without abyssus.
2. 100 base damage, 10 after 90% reduction. With 40% on the helmet, 40 of 100 damage will be applied now, making the incoming damage not 10, but 50.

I'm slightly confused as I did the merci Lab yesterday while wearing the helmet, and the phys dmg traps nearly killed me. In theory, with 90% reduction, I should even notice them shouldn't I?

Please keep any spelling mistakes, english is not my first language.

[Grumpy]

damage taken is calculated after all mitigation.

[Linkk]

You can look it up in detail here:
https://pathofexile.gamepedia.com/Receiving_damage

[Drake]

Reduced and increased are additive. So if you have 90% physical damage reduction and abyssus has 40% incrased it's going to be 90-40 so 50% damage reduction.
Making the second option the right one.

Then very important thing to understand with physical damage. If your 90% reduction are taking into account armour, that number doesn't mean anything. The damage reduction calculated from armour depends on the hit you take, since armour is not linear, the more damage you take from a hit the more armour you need to counter it, like if you can mitigate all of 100 damage with 500 armour, 1000 won't mitigate 200 damage, you might need 3000 for that (numbers are made up, but the ratio is not).
So that 90% might become 30 or even 20% if you take a critical strike.

Then there is the case of traps, physical traps deal hp based bleeding damage. So armour doesn't do anything since it doesn't work on dot damage from bleeding. When you run into traps you could be naked it would be the same, except that abyssus debuff still applies, so yeah, if you run into them, you die.

[Grumpy]

Originally posted by Sajah:

Reduced and increased are additive. So if you have 90% physical damage reduction and abyssus has 40% incrased it's going to be 90-40 so 50% damage reduction.
Making the second option the right one.

not really. damage taken comes after everything else, its the last part of the chain. so if he would get a 10 dmg hit because of 90% reduction, he would suffer 14 dmg with abyssus.

abyssus would completely broken when it would remove all your phys dmg reduction with a 40-50% roll.