I don't have as much time to work on this as I would like, and I've been meaning to for a while. But I will give you some basic reasoning as to why I prefer this build over any other Shaco build.

To begin, this is a chart for damage mitigation from armor and magic resistance.




A standard Marksmen for example at level 18 has around a base armor of 82, and a magic resistance of 30. Just by base, about 44% of your physical damage, and 23% of your magic damage will be negated.

So why is this critical?

Well because if you play AP or Crit Shaco, you're going to be doing a lot of hybrid damage. Hybrid damage can be good if it's consistent (I.E. Kogmaw, Shyvanna, Jax), however Shaco is all about his burst, he has no consistent damage. This means you're going to want to do as much of the damage your meant to as possible, but then you run into a large issue. You can't specialize into both armor penetration and magic penetration on your items as a burst assassin. If you build critical Shaco you're more than likely going to be grabbing a static shiv, which does magic damage, not to mention your two shiv poison. If you build AP Shaco, your JiTB, Two Shiv Poison, and Hallucinate all do magic damage, but your Deceive is pure physical damage.

Then another issue arises.

If you're focusing on your magic damage, there aren't many flat magic penetration items that synergize with Shaco's burst. Same with crit Shaco; if you buy a last whisper, you only shred BONUS armor, not that 82 base armor.

This is where lethality comes into play.

With lethality Quints, Marks, the precision mastery, and the three lethality items: Duskblade, Youmuu's, and Edge of Night, you bypass 82.5 armor. You effectively tear through every point of base armor a standard squishy champion has. You essentially do true damage with your Deceive.

This is as much as I can add for now, will come back to this later