I recently bought Yasuo, and being myself, looked at as many guides as possible. Then, I looked at how his abilities revolve around stats, and thought Why don't people build Phantom Dancer as their second item on Yasuo? I'm only level 18, so there is probably a reason, just wanted to know what it is.
P.S. If perchance I'm right, why is it better than other items on him?
This question has been answered, and i do not need further feedback.
it's crit overkill basically. shiv and PD together give 55% crit, or 110% with his passive, which means 10% goes to waste automatically. Additionally, since Yasuo has a reduced crit multiplier (something like 190% or 180% instead of 200%), he really needs IE to actually deal significant DPS later on, which with both other crit items would leave him 50% over max crit. Also, going for 2 AS+crit items without any AD for the crit to multiply leaves your DPS behind.
Personally, I think PD+IE is a fine build, it doesn't offer quite the same powerspike as Shiv because you don't get the magic damage from its passive, and you do go slightly over the crit cap, but having that extra 20% crit from choosing PD over Shiv makes it worth later on in the game.
Imo, the best build for Yasuo currently is 
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A crit built without IE is pointless and getting all three items on Yasuo is useless overload.
Shiv is betetr than PD becasue the extra damage is critical more often and he doesn't need the phantom passive because he already got abbilities for that.
Crit chance and attack speed are nice, but you need AD to actually deal significant damage. In addition, Infinity Edge or desirable due to the amplification of crit damage, which would put you over the top with SS and PD already purchased, wasting gold.
If you need more attack speed, get Blade of the Ruined King instead of Bloodthirster.
Yasuo's Crit Chance is doubled as part of his passive, in return his Crits only do 80% of the damage of normal Crit damage, so normally an attack that would hit 100, is doubled to 200 by crit, however since he only utilizes 80% of his crit damage the damage would be 180. So shiv gives 20% crit chance (40% for Yasuo) Infinity edge gives another 20% (40% again for Yasuo) so he has 80% crit chance by this point, get another 10% from runes, this is the basic Yasuo build i would recommend to players, but its actually better to go Triforce after Shiv like they are doing in China.
As others have said there's two simple reasons.
AS+Crit without lots of AD is not very worthwhile, especially on Yasuo who deals reduced crit damage.
You overcap your crit chance just with those two items, and if you get both you're guaranteed to need Infinity Edge to boost your crits higher.
If you really really want more attack speed and crit then build a Zeal into Trinity Force.
If you have Shiv, Phantom Dancer adds nothing because you need IE and that gives you all the crit you need, and there are better options for attack speed/movespeed.
Even PD's collision ignoring passive is less useful on Yasuo because of his infinite dashes.
shiv first for the stats and burst, then ie for the crits and damage. if you go PD you are only going to do so much damage, you delay your damage and will have well over 100% crit chance when you get ie
You guys do know building AD Yasuo is almost as good as critsuo? imo he's almost as cheap as teemo
He will get over 100% crit which is wasted stats
you do realise he has double crit chance right? you go shiv + IE and you have 80% crit. if you build shiv, IE and PD then you have 150%. why would you want to overload on crit chance like that?
you can go shiv + IE and then pretty much anything. blade, bt, trinity, last whisper, maw, whatever. go nuts. literally all of your hits will crit so just build what will be best for you once you have those two core items.
I main Yasuo and speed is very important and phaeton dancer could be useful, but speed does no damage. You need to hit very hard because by the time you have shiv most have armor and/or are too high level to be hit with your base damage.
shiv gives yas 40% crit infin gives yas 40% crit
now you have 80%
phantom dancer alone gives yas 70% crit and anything over 100% is wasted stats
I'm just trying to say that, if someone were to rush phantom dancer before infinity edge, they would get to 100% crit, And would have full cool down reduction on his Q, before they would if they were to build infinity edge first.
After Shyv of course.
