Kha'zix is a really strong assassin with lot of burst damage, his ultimate allows you to escape or reset his passive for slow , if you evolve E any kill or assist refresh the cooldown giving you the chance , for example ,to do a tower dive very easily.
Kha unlike the other assassins can make a lot of burst also in late game that makes him one of the best assassins.

Kha is mana dependent ,so buy a lot of potions and take blue.

PASSIVE:
Unseen Threat
When Kha'Zix is not visible to the enemy team, he gains Unseen Threat, causing his next basic attack against an enemy champion to deal 15 / 20 / 25 / 35 / 45 / 55 / 65 / 75 / 85 / 95 / 110 / 125 / 140 / 155 / 170 / 185 / 200 / 220 + (50% of ability power) bonus magic damage and slows by 25% for 2 seconds.

Kha'Zix's passive is what makes him a great duelist and great initiator of teamfights with his evolved W. In duels you may want to use his ultimate to proc the passive for slows.

Q:
Taste Their Fear
Passive: Marks isolated targets.

Active: Deals 70 / 100 / 130 / 160 / 190 (+1.5 per bonus attack damage) physical damage to a single target. Damage against isolated targets is significantly increased to 100 / 145 / 190 / 235 / 280 (+2.0 per bonus attack damage).

Evolving claws increases damage to isolated targets by 12% of their missing health. Kha'Zix also gains 50 increased range on both Taste Their Fear and his basic attacks.

W:
Void Spike
Kha'Zix fires spikes that explode on contact, dealing 75 / 115 / 155 / 195 / 235 (+0.9 per bonus attack damage) physical damage to all nearby enemies. Kha'Zix is healed by 40 / 70 / 100 / 130 / 160 (+50% of ability power) if he is within the explosion radius.

Evolving spike racks causes Void Spike to fire three projectiles in a cone. Spikes will also apply Unseen Threat to all enemies caught within the area of effect.

E:
Leap
Kha'Zix leaps to an area, dealing 65 / 100 / 135 / 170 / 205 (+0.8 per bonus attack damage) physical damage to enemies in the area he lands.

Evolving wings increases Leap's range dramatically and causes a kill or assists to refresh the cooldown of Leap.

R:
Void Assault
Passive: Each rank of Void Assault allows Kha'Zix to evolve one of his active abilities, granting it an additional effect.

Active: Kha'Zix enters stealth for 1 second and gains Unseen Threat, gaining 40% movement speed. Kha'Zix can cast Void Assault again within 10 seconds after activation. There is a 2 second cooldown between each cast of Void Assault.

Evolving active camouflage allows Kha'Zix to cast Void Assault three times within 10 seconds and reduces any damage by 40% he takes while in stealth.

Kha's evolution can have a different order according to player's role and play mode, e.g., if Kha is used in a siutation where you are against a ranged that doesn't let you farm, you can evolve your W to give you the chance to do more creeps and to harass your enemy without engaging or taking damage.

If you are against a character with a lot of escapes (e.g. Kassadin) you can evolve your E (I prefer evolving this last, though), useful in teamfights because his evolution passive makes the skill refresh.

Q and R are evolved last 'cause they're less important than the other unless the escape with the final.
If you need to escape from tough situations,then you last evolution should be R otherwise,if you want to deal HUGE (trust me,ridicolously HUGE) Damage then your last Evolution shoud be Q.

For runes go
Mark - x9 Attack Dmg.
Seal - x9 Armor
Glyph - x9 Magic Res.
Quintessence - x3 Attack Dmg.

For masteries go 21/4/5

Start items
Can also
Vs AD Mid build like this
or Vs AP Mid make
or Situational items

and

or

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