Hello, this is my first guide, so please bear with me and don't rate until you read the whole thing.


What you are about to see is simply how I prefer to play Kha'Zix, and all of it may vary depending on what the enemy team has. I play Kha'Zix to max out his burst damage, and single out the enemies until only the tank is left. If that's not how you plan to play Kha'Zix, then you should find another guide.

Pros:
Kha'Zix excels at 1v1 combat, and can easily burst down most squishies.
Dominates when enemies are out of position
Good burst
Good survivability
Gap closer/ escape
He's the alien to Rengar's predator!

Cons:
A bit mana dependent early game
Countered in large groups
Hard CC vulnerable
Easily focused if not played right
Takes practice
Squishy

Your Q is perhaps one of the most unique abilities in the game, dealing FAR more damage if the enemy is alone, and near no minions. The amount of scaling it does when isolated makes it a threat to be feared, as it rightly should.
Your passive is also unique, and utilizing it can turn a bad situation into a good one pretty quickly, even when not building ability power.

These runes are just my basic AD bruiser runes, with AD marks, Armor yellows, Mresist blues, and Arm. Pen quints. I choose these because I think it gives you a sort of jack-of-all-trades sort of rune set that can deal with most situations.

I like to use these runes because it gives you a headstart to most situations, however it wont fully negate problems. I choose AD marks simply because I bought them when I played akali, and I figured that I'm not going to buy more AD runes. Pick up the Arm. Pen quints to make up for the marks. (you could do Arm. Pen marks and AD quints if you wanted).

The Mres and Armor runes are also variable, but I choose them for resistance against the enemy AP mid, and the AD carry. It might not be much, but it's something.

I chose these masteries because I feel like it optimizes Kha'Zixs's early game jungling, while not sacrificing much late game.
Offense:21
3/3 Brute Force: 3 more attack damage? Why not!!!
1/2 Butcher: 2 more damage to minions, however little it is, it helps.
4/4 Alacrity: 4% attack speed. More attack speed = more attacks = more win.
4/4 Deadliness: .5 AD per level? Heck yes!!!
1/1 Weapon Expertise: +10% Armor Penetration - Those pesky tanks.
1/1 10% Critical strike damage: Higher crit damage = not really necessary, but its a filler.
3/3 Vampirism: STACK THAT LIFESTEAL BABY!
3/3 Sunder: 6 armor penetration - More tanks!
1/1 Executioner: 6% more damage on foes below 40%... Need I say more?

Defense:9
1/3 Resistace: Just some defense from the AP carry when you gank.
1/1 Summoners resolve: 10 more gold from smiting.
2/2 Tough Skin: 2 less damage from monsters. Yay!
4/4 Durability: 108 health at level 18! Who knows if that'll be the health that saves you from ignite.
1/1 Veteran's Scars: Straight up 30 health. A nice touch. Take either this or bladed armor.

I choose smite and flash, simply for extra gold and mobility. Plus smite makes jungling easy. Flash is like the right hand man of summoner spells, but another good one to have would be ignite, ghost, or exhaust.
If the enemies have lots of escape, ghost or exhaust might be good for you to grab instead of flash, so you can catch up or you can slow them down.
Ignite is a "meh" spell in my opinon, and is extremely overused.
Teleport is another good one if your team is actively warding, so you can teleport to a ward behind them while they're running.

Spells to avoid:
Heal- Seriously, don't use this. Its really just not worth it, and it'll make you look really bad.
Clarity- Equally as bad as Heal.
Surge- The attack speed buff from it simply isn't enough to make it fully useful to me.
Revive- I don't know why anyone would ever want this spell, but it just wouldn't be good.
Promote- You're not laning.
Last but not least, Cleanse. - Despite how useful it can be, I don't think that it is better to use than Exhaust, flash, ghost, teleport, or ignite.

I choose to start with my Q for extra damage on Blue buff and wolves, then the W for health and AoE damage. Level up W again for more health/AoE, and then your Q/E, depending on whether your lanes need to be ganked or not. Max your Q first, then you W, then your E. Do this for more damage on your ganks, faster camp clearing, and level E last because it serves as a gap closer, and doesn't deal as much damage. For evolving, I choose to evolve my Ultimate, Q, then E. Why I do this is so I have another chance to take down my opponent, and a higher burst when they are alone. The evolved leap is so you can leap in, kill the enemy, then leap back out.

If you find the enemy team grouping alot, evolve your W instead of your Q for more AoE and more influence in team fights.

Now, I build Kha'Zix like this normally, just because at the moment; Lets just say I was hitting 1k on isolated targets. The extra lifesteal lets you escape into the jungle/ a minion lane after a fight and heal up quicker; minimizing the need to recall.
Start 5 pots and a cloth armor (or 9 pots and a ward), and start wolves- Killing the little ones first for max damage on your Q. Continue on to Blue Buff, and do the same; asking for a leash on the little monsters. Level up your W and go to wraiths, then after leveling your W again (for extra AoE damage and a bigger heal) go to red buff (if smite has a cooldown of less than 20) or Golems if it is greater.
At this point, if all of the lanes are doing well, level up your Q and continue jungling.
Buy a vampiric scepter, and farm until you can buy a phage. After that, keep farming and ganking until you can buy a BF sword, and finally a bloodthirster. With that you should have more sustain in jungle. Buy a frozen mallet, and follow it up with an Infinity Edge OR a Phantom Dancer. The next two items are optional, however I like to get two more bloodthirsters to deal even more damage on my Q.

Many Kha'Zix players I have played with don't realise that they can use their ultimate to avoid turret fire. Well, if you time it right, you can; which may very well save you from a dive-gone-wrong.

When a target is isolated, initiate with your leap and immediately Q them. Use your W, and Q again. If they start to run (which they should), you can pop you ultimate to gain a speed buff and stealth for a second, also refreshing Unseen Predator. With enough AD, most ganks on squishies will only take a few seconds.

Overall, Kha'Zix is a very unique champion. He excels at 1v1 combat in secluded areas, but struggles a bit in large team fights. To play him effectively, DON'T jump headstrong into the brawl- wait for the enemies to spread out, and single them out 1 by 1.

How you choose to evolve your skills is entirely up to you, and how you plan to play. upgrading your W gives you more... "ooomf" in team fights, whereas upgrading your Q gives you a higher picking-power. Definitely upgrade your Ultimate and your E though, as they are essential. I personally upgrade R, Q, E.

If you find yourself being constantly focused in team fights, wait a little bit longer to engage so the enemies wont see you first.

Despite how difficult Kha'zix may be to play, in the long run he is worth it. He can stomp on anyone who plays out of line, or is positioned poorly.
Thank you for reading, don't forget to rate, and good luck.