League-of-legends – How does Corki’s passive work

This is straight from the LOL wiki:

http://leagueoflegends.wikia.com/wiki/Shaco_the_Demon_Jester/Strategy

The bonus critical strike damage from Infinity Edge will apply on critical hits from Deceive, in addition to the bonus magic damage the ability gives.

So to answer your question: Yes Deceive benefits from Infinity Edge. It stands to reason that it will also benefit from Crit Dmg Runes. With that said, the following has been taken from League Craft forum posts: http://forum.leaguecraft.com/index.php?/topic/6388-shaco-deceive-crit-dmg-runes/

Not sure about the math or the mechanics behind it, but I just tested Deceive at level 1 on a Master Yi at level 1 in a practice game, once with a full page of Crit Damage runes and one with some other random page that wouldn't affect the damage. All other factors were kept the same both times. Results: Without Crit Damage runes: 64 from the front, 80 from the back With: 85 from the front, 100 from the back

Of course, that was in June 2010...

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.