WARNING: this guide is for people that know how to play not the First timer. If you don't get what I'm saying try looking at a different guide PLAY some and then come back when you figure out how to use Hextech Gunblade.

Whenever you slow someone down you are able to pull off most of your R so Hextech Gunblade and Exhaust are a must. the faster u get Hextech Gunblade the faster you win. Use W-E-Hextech Gunblade-R-Q or W-Q-E-Exhaust-R or Exhaust-W-Q-Hextech Gunblade-E-R or however u think you can use them u can use them the Gunblade is so good that u cant not have it!

Why use Flash when i have Shunpo? Oh just because it's the best skill. Ok, you want to turret hump with little health Shunpo in Flash out.

I try to get most base Stats runes so i have a good start with 1-3 over 1-18LVL
Heath: is good for the start makes you last longer then the opponent.
Cooldown: one of the best stats for Kat, who only has to worry about cooldowns.
Magic Penetration: All your moves are Magic.

You are not a tank know your place. Lot of the time you will be the last one alive people are going to get mad but that's the game find the right time to Slow and Spin To win.