Do abiities or masteries like Harden Skin, Defensive Mastery, or Amumu's Tantrum reduce damage before or after resistance? Because if it's before, the damage reduction is completely negilible, even against minions. They do what vanguard and Kraken's shell did in Dota, but the bonus is so small, it may as well not even be there.

Also, I'm not really sure if armor reduction is really granting a 1% bonus. I was just playing Ramius and I was taking 20 points of damage against the dragon minion with shell on, and when it wore off, I was taking 26 damage. If 150/150 armor/magic reduction worked as you described, I should have been taking 40 damage after shell wore off. As it is, it would seem that either armor or magic, probably both only grant .25 hps per point.

For every 100 points of reduction, I should be cutting an enemy attacks in half. Clearly not the case with my example.

That's good to hear. That kind of damage reduction is only really good if have something in front of it.

However, back to my other question, I double checked, this time in a practice game. This time the dragon dealt 56 damage without the shell, 39 with level 3 shell (100 armor/magic res). Now I have three points in Harden Skin, but I that's only two points of damage reduction. Something is off, since 100 armor should have cut that 56 points of damage in half, down to 28 or so.

Either shell is bugged, armor/res is bugged, I'm mistaken somehow, or the mechanics page needs to be updated because it's not working as adertised.

I mean, really. If I'm only gaining .5% effectiveness for hps, then items that grant raw hp gain are clearly a better investment, since adding hp provides protection against both magic and physical attacks.

So let me see if I got this straight

Let's say I have 100 hp 0 armor. I buy 6 items that increases my armor by 100 each. That would be like adding 600 hp, effectively, right?

Now let's say I instead buy 5 items that increase my hp by 100 each and 1 item that increases armor by 100. That's 1200 ehp.

Given that, and considering the potency of both magical and physical damage in this game, is there really any incentive at all to increase armor or magic resist over hp?

Question:
If I have one infinity edge (crits do 250% instead of 200%) and +8% crit damage from runes... how does that stack? Is it (a) 258% crit damage? Or (b), the +8% taken after the 250%?

In the case of (a), new damage = damage x 2.58
In the case of (b), new damage = damage x 2.5 x 1.08

Which is it? Thanks!

I can easily give a counter example:
well what if you have 3000 hp and 100 armour, whats better against physical attacks 50 more armour or 600 more hp? Which is cheaper?
Answer: Assuming no recipe items the hp route gives 7200 ehp vs physical attacks for roughly 1425g. While the armour route gives 7500 ehp vs physical attacks for roughly 700g.

The problem for now with armour is that one item really reduces the effectiveness of armour. The same cannot be said for MR. Buying some MR is worth it.
Many champs have 1.5k-2k base hp at level 18. While only have 30 MR. buying MR will make many caster champs like veigar lose a lot of their burst effectiveness against you (especially if you get veil as part of MR and immunity once every 25 seconds).