Make sure to Evovle lv 1 is "Q", 2 is "E", 3 is "R"
This is really important!
Reasons:
Evovle 1, its basicly because of an truely burst. This helps alot!
Evovle 2, If u chase, or are getting Chased, the "E" will make you jump away, or after them easily.
Evovle 3, This is good for your passive, and to assassinate the target, and if you're getting alot of dmg, or ganked, u can always use it to get away. :-)

If you are playing vs an AD TOP AND MID. Make sure to purchase the Armor boots instead.
Same if it is AP at both of the lanes, buy Magic resist boots then.

The mana regen makes you gain more Health Regen, and with Manamune, its way to powerfull.
If you dont like it, you can always change it to defense, or even more offense.
These masteries is also good for chasing, Escapes, and 10 Procent more time for the elixer to give you a great start at the toplane.

When you fight your enemy at the toplane.
Make sure if you are going to engage to puff the red elixer, this will make it easier til kill your enemy, and give u alot of AD, Health.
If your enemy goes hard on you and your almost dead, and he like.. puffed ignite on you, you can use your elixer to survive the dmg from the ignite.

Reason:
Bloodthirster, More AD.
Manamune, More mana + Upgrade for insanly dmg, and slow. - With the Utility masteries you will also gain more Health Regen.

IT IS REALLY REALLY REALLY Important if you want to burst your enemy make sure nothing stands with him, then he gets isolated.
Isolate will make your "Q" Hit 50Procent Harder. Which is alot, specially with this killer build.

Thank you for watching my guide, if you like it, please vote it up for the rest of the people who wants to play Kha'zix :-)
If you think this sux, pls dont just dislike it, but also make a comment or something. so i always can change it.

Thank you.

- UnknownClipz.