Originally Posted by TK464
It's quite useful, the CDR/Mp5 alone is excellent for him. The AS lets you proc his passive more, and the thing to remember is often times as AP Yi you'll need just a bit of damage to finish someone when your Alpha Strike is down. Also remember he has Wuju/Highlander so with just a Nashors you're gonna be hitting incredibly fast during your ult and with a decent bit of damage against squishies.
EDIT: Silly me, thought you said AP Yi. Either way my post still works.
If you want to att hard and fast I suggest...
(Btw, this is an AD/AS/Crit build)
Zerker boots (Merc's if they have a lot of CC)
Black Cleaver/Starks/Bloodthirster (This item depends on team comp)
Situational item (Defensive or Offensive)
Executioner's Culling (if no ignite on team)
EDIT: I don't get 2 Phantom dancers because I think the crit and AS from youmu's, 1 PD, the IE and your Highlander is plenty of damage. The elixirs (especially red and green) help out greatly too. I'm not a big fan of pure glass cannon as a melee character.
Feel free to ask if you want me to elaborate of a specific item choice.