I've been thinking of spicing up my Rammus play with some variance, and one thing I've been looking at is the armor Leviathan, which grants health in a snowball fashion. At max stacks, it reduces damage taken by 15% (which sounds similar to the 4% reduction you can get if you have enough Defense Masteries). As a tank, and as Rammus specifically, I tend to get a lot of assists which helps build up to that 15% reduction.
That got me thinking, how does this interact with some of the various other methods to reduce damage, though? There are at least 3 methods I know of.
- Armor/Magic Resist – Detailed quite thoroughly here.
- Reduce damage by fixed number – Amumu's Tantrum has a passive that does this, and there's also a Mastery that affects this.
- Reduce damage by percentage – The aforementioned Leviathan item and the Mastery.
What is the order in which these effects are applied? Do the latter two apply to the damage after armor/magic resist is factored in, or do they alter the damage prior to calculating armor/magic resist? Are there any other methods of damage reduction that have their own special effects for this?
If it's not too far off to simultaneously address, do damage amplifying effects like Vlad's ultimate counter the corresponding damage reduction methods, or do they multiplicatively stack with the results at some stage?
This question covers how normal attacks benefit, but it doesn't happen to cover these specific effects and how they synergize with each other.
Best Answer
Okay, from my experiments, it goes:
Armor/MR reductions <--> Percentage Reductions
(They stack multiplicatively, so order is irrelevant)
Flat Reductions
This makes sense, since if flat reduction was the first thing applied, after armor, it may have failed to provide a benefit at all (since, for instance, the difference between 50 * 27% and 48 * 27% is minute at best. 50 and 27% being the base attack damage of Ezreal and the armor of Amumu, my two test characters.)
Shields act as health, and damage done to shields is likewise reduced by armor / magic resist. (Meaning shields on tanks can generally absorb more punishment than shields on squishies)