Mathematically Correct Kha'Zix (ss12)

Mathematically Correct Kha'Zix (ss12)

Chilling Smite
VS Squishy 
Only use this if you have Nimbus Cloak 
Challenging Smite
VS Bruiser 
Skill Order:
Taste Their Fear
Void Spike
Void Assault

UPDATED PATCH 12.23: Ravenous Hydra is broken as hell even if you don't get as many stacks as a jungler. Abusing the hell out of it for free LP. Ravenous first item + early kill and you'll snowball like crazy. I'm expecting a nerf toward ravenous soon.

-Introducing: I'm a Diamond 4 Kha'Zix mains who plays on Vietnamese server. I have played over 2300+ games of Kha'Zix since season 9, had 800k mastery on my main account and 200k mastery on alt so I have decent knowledge about his strengths and weaknesses. The reason why I made this little guide is because many people are building Kha'Zix wrong and I'm here to lead you to the right build.
-About this build: Trying to maximize damage from Q (Taste Their Fear) while having enough sustain and tankyness to duel every single champion in the game. With over 200% ratio with AD on Q, maximize the damage isn't really that hard since Q already scales very well with lethality.
-There are currently 3 build which you can go: Eclipse/ Prowler's Claw/ Bruiser build with Divine Sunderer. But in this guide, I will only be talking about Eclipse build, which IMO, is currently the best mythic item for Kha'Zix.
-Why no Duskblade? Yes I know, this can be a bit confusing. Everyone goes Duskblade, then why I don't suggest it? Trust me, Duskblade is overated af. Its passive is most of the time useless on Kha'Zix and its effectiveness is nothing compared to other mythic items like Eclipse (which is the BEST item for Kha6 right now). Even if you bought it for the invisibility, it's just not worth it, there's no need for more invis when you already have a lot of mobility with R, Evolved E (also Phase Rush, Blue Smite, Nimbus Cloak if you follow my build); it's enough for you to get more than 2 kills and get away with it. Honestly, I don't see any situations which you build Duskblade, since you can E Q aa and get a kill easily with any of my build anyway.
TL;DR: Lack of damage compares to every other core mythic items. Don't get me wrong, it's still viable up to challenger level but in order for it to work, you really have to trust your bronze teammate (LOL). Moreover, that build requires some times to get used to and overall offers completely different playstyle (you have to play like a rat) if you want to get the max out of it.

Let's just get straight into the build here: Full lethality & armor penetration to maximize Q damage. "The best defense is a good offense".

-First item is Ravenous Hydra (surprisingly). It's very broken at the moment with over 53% winrate on every role. Buying Ravenous makes your clear much, much faster thanks to the AoE. The downside of this is that death often loses you many snowball power but this is minimized by the fact that you can stack it all the way again. 

-Eclipse provides anything an assassin need: damage, sustain, and movement speed. With its component extremely efficiently on Kha'Zix (life steals is really good on Kha6, who would've thought?), it's easily being the BEST item on Kha'Zix. Second place belongs to Prowler's Claw. It used to be the best item you can build on Kha'Zix due to its mythic passive plus 5 on every legendary item you have. Which means if you have full build, this single item can give you up to 46 lethality (??!?), which is insanely OP. But in patch 11.13, it has been nerfed quite a lot, from the raw lethality it gives, to its active cooldown. So well, we have to change for good no matter what like the wise Kha'Zix himself once said:"Consume and Adapt".

-Boots: honestly, anything is good here. You can either take defensive boots, or offense, it's a matter of personal preference. You can even go for swiftness boot or no tier 2 boots, saving gold for powerspike item if you're fed. The only exception here is the cdr boots. Personally, I don't think cdr is really any essentials to Kha6 unlike Zed or Rengar so I don't really build it often. But maybe you can try it out to see if it works for your playstyle..?
-Next item, Ghostblade. Very standard here, nothing too special. Movement speed when out of combat? Seem good to me. Lots of lethality? We take those. The Collector is not our option here. Very interesting passive but anything besides that it is just a waste of gold. Less lethality, bad gold efficiency, pass.
-Next item, Essence Reaver. "Seemingly out of nowhere, sheen item on an assassin? But you said this build is full lethality & penetration? " Before you complains and leave the page, hear me out. Do you know the only Kha'Zix weakness is? His kit relies way too much on isolation, (Q deals 110% more damage against isolated target, W evolved slow 90% against isolated target) which is rarely the case in high elo. This build is not created for low elo only, but also high elo or team comp that doesn't give you chance to hunt down isolated target. Thinking about that for a moment, this item came into my mind. So after many testing on practice tool, this idea got my surprise. Sheen passive which synergizes very well with Kha'Zix passive, dealing a whole lot of undodgeable damage to enemy. Plus when you burst down any target, let's say their adc, you would want to auto attack first (or Q mid-air if possible) for the slow anyway. It's INCREDIBLY good! With these 4 items, . This item also makes clear camps or taking down drake much faster. Essence Reaver DEFINITELY got a slot in this build. On top of that, it makes sure you don't run out of mana while in combat. 

- I would love to have a slot for Essence Reaver but sadly there's only 6 item slots ;(

-Fifth item is Serylda's Grudge or a defensive item. You got more than enough lethality and heading to mid-late game, therefore the only thing you need now is some more armor penetration or defensive item (. There used to be a time where you had the option to either build Serylda's Grudge or Lord Dominik Regards (LDR) but after the nerf to LDR, Serylda turned out to be the superior one. The perma slow is great and can single-handedly win you the fight sometimes. -Last item is situational. It can be any items really. At this moment you don't really need more damage anymore so building defensive should be the main priority but there's nothing wrong with having more offense. Last item could be: + Death's Dance: Good overall vs AD comp. + Guardian Angel: Good overall vs AD comp. + Edge Of Night: Prevent CC or range abilities (Lux Q, Zoe E, Fizz R, anything has a lot of range that can one shot you from miles away). + Maw Of Malmortius: Good against AP comp. + Bloodthirster: More damage. + Frozen Heart: Against 4 or 5 ADs. -Skill Order: Q -> E -> W

IMPORTANT: DON'T MAX W SECOND, PUT 2 POINT ON W THEN MAX E AFTERWARD (E is much more important mid game duo to its low cooldown when being maxed)

  -Evolve Order: Q -> E -> W if their enemy team has 3 or more squishies, otherwise Q -> E -> R. R is good for extended teamfight while W is good at isolating and bursting down single target.