League-of-legends – How does critical strike chance stack

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...

The Default critical strike chance of all champions and non-wolf mobs is 0%.

This wasn't true back during the beta, but in present day LoL, it is impossible to get critical strike chance without runes or items.

Notable perceived exceptions are Ashe and Tryndamere, who get crit from their passive abilities, but these buffs adjust upwards from the same base of 0%.