league-of-legends
Death Fire Touch deals different amounts of damage depending on the skill used to apply it. I'm most interested in what happens when playing Cassiopeia. Q is a damage over time skill and applies it for 1 second but E is single target and applies for 4 seconds.
If I hit an enemy with E to apply it for 4 seconds, is it overridden with a 1 second duration if I land a Q or will it keep the remainder of the 4 seconds?
First, let's clear up a misconception.
Armor Penetration gives you a constant %damage bonus, regardless of how much armor the enemy has see here.
It doesn't matter if your enemy has 300 armor or 15 -- penetrating 10 of that will have the same effect on total DPS increase.
That said, let's take a look at why Armor Penetration is preferred, even with its linearity.
Attack Speed is easy to acquire via items.
Armor Penetration is not.
You can more than match the effects of attack speed runes with a single dagger - 420 gold.
The cheapest item with Armor Penetration is the Brutalizer at 1337 total gold. By this metric alone, Armor penetration runes are worth approximately three times that of attack speed runes.
It is easier to use items to stack Attack Speed over Armor Penetration -- but to get the highest DPS, you want to stack both.
Given that the amount of Armor Penetration available via items is strictly limited, if one's goal is to achieve maximal values for both Armor Penetration and Attack Speed, runes for Armor Penetration are much better than that of Attack Speed.
Alright, The awesome FallenAngelEyes helped me do some science and here are the results:
With Evasion:
Without Evasion:
As you can see, Requiem does not get reduced by the Evasion mastery.
I ran the same set up for Karthus both times (gear, runes, and masteries).
Best Answer
Here is the wikia page on Death Fire Touch