Glass Reaper is designed so that you will do the most damage possible in a huge burst that will surprise your enemy.
You are going to use the element of surprise to its very best. You are going to be taking out enemies so fast that they wont even be able to react and fight back.

Make sure to read all the notes on items and abilities for a better explanation of their use

This build works best against squishy champions or ranged fighters.

Glass Reaper Kha'Zix has its advantages and disadvantages.

-Advantages-
It does an insane amount of damage in bursts or in all out combat. It also has incredible fast minion clear time allowing for very efficient farming and pushing.
-Disadvantages-
You are very squishy and may not fare well in team fights if you are targeted first.

As the Glass Reaper, you are a Glass Cannon that packs one hell of a punch, and will therefore want to avoid being targeted as much as possible. You should try to get the drop on your enemy and hit them first, and hopefully finish them before they hit back!

-How to kill an enemy-
All of your abilities should be used when trying to kill an enemy.
The first thing you should try to do is to find a place out of the enemies vision where you can use you VOID ASSAULT ultimate and start towards them without them noticing you coming. Close the gap as your invisibility wears off by jumping on to them. As soon as you land you will want to use everything you have on them in a burst and land at least one auto-attack to use your UNSEEN THREAT passive ability which will deal extra damage and slow the target substantially, allowing for as much more damage to be done as possible in the small period of time. You will want to use your second hit on your VOID ASSAULT before it goes on cool-down, and this will also activate UNSEEN THREAT again to give more damage and keep your prey from fleeing.

If your prey flashes before you do much to them, that is perfectly fine since VOID ASSAULT has a fairly short cool-down time, and you just made them burn a flash which will take much longer to be back up, giving you time to prepare for another attack.

If you find yourself in the jungle trying to hunt down some prey, make sure to make the most of your terrain with your LEAP, and get them by surprise if you can by using VOID ASSAULT in a bush or around a corner if you are closing on an unsuspecting enemy.
I highly recommend that you familiarise yourself with what you can and can't jump over, as this can mess you up and leave you sitting there, on the wrong side of the wall, with now way to get over now but to go around and let the kill escape. LEAP can be very finicky and you will get caught up on the smallest things that you might not even notice, so be careful when jumping that you have a clear path that you know you can get across.

Try to make sure you get second Blue Buff from your jungler as the mana and cool-down reduction help greatly. Red Buff has that extra bit of damage and the DOT effect will also help to get and prey that escapes with little health left.

By late game there will be a lot of fighting done and you will want to be a part of it. In a team-fight, the first thing you should do is use VOID ASSAULT so you won't be targeted as quickly. Burn as many abilities as you can in a fight, and try to target the main damage dealers such as the ADC or APC, and then proceed to take out enemies in the order of their damage:health ratio. The more damage an enemy does, that faster it should die, and who better to ensure that than the Glass Reaper himself.

Kha'Zix is a great lane pusher too, since he has plenty of damage and can get out of a situation quickly if needed.

Kha'Zix has the ability of evolution, and every time he puts a point towards his VOID ASSAULT ultimate, he gets an Evolution Point.
These points are used to permanently upgrade any of his abilities to an improved form with improved abilities.

-Evolutions-
TASTE THEIR FEAR - EVOLVED ENLARGED CLAWS increases the range of TASTE THEIR FEAR and autto-attacks by 50. Also, he now does 8% of the target's missing health in bonus damage (max 200 on monsters). Deals 45% more damage to 11.6% of the target's health against isolated targets.
VOID SPIKE - EVOLVED SPIKE RACKS changes from 1 missile firing strait forward, to 3 missiles firing in a cone.
LEAP - EVOLVED WINGS increase LEAP's range by 300, and kills and assists will now refresh LEAP's cool-down.
VOID ASSAULT - EVOLVED ACTIVE CAMOUFLAGE allows VOID ASSAULT to be cast 3 times, and Kha'Zix takes 50% less damage while invisible.

THE HUNT IS ON!
According to the lore, Rengar and Kha'Zix are enemies, and want each other dead. After a vicious battle between the two, Kha'Zix found Rengar to be a formidable opponent who he could learn some from. Kha'Zix wants to consume Rengar, learn his abilities and become the ultimate predator.
In game, once Kha'Zix has use all 3 evolution points, and Rengar has a Bonetooth Necklace with at least 10 stacks, and all players are alive, a quest starts called THE HUNT IS ON! and whichever of the two kills (or assists in killing) the other receives a bonus. If Kha'Zix wins, he gets a fourth EVOLUTION POINT.
If Rengar wins, he gets the item HEAD OF KHA'ZIX.