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-Pros

Teriffic mobility

Easy to kill enemies with combos

Massive R damage

Almost easy to Master

Cons

Easily focused at teamfights

Can be countered easily

Only for Bronze to Gold

I am sure that you all know that Kata is not as easy as it seems. Skills and brain are required to succeed a dive in a turret or at teamfights.
Lets see the combos:
Level 1-3
(E-W-Q-E) the basic combo. Use E to get close, W to damage(catch the dagger), Q the enemy when he tries to escape and then E on him.
Level 6
(E-W-R-E-W-Q-E)
a big but simple combo. Same with first, but insteed of E again open your R. Interupt your R when the enemy tries to escape with your E and then W and etc.

Kata isn't a tank champ which means that u can't dive into 5 full HP enemies alone, without having any skills. Wait for your team to dive first and then Q-E(on daggger)-R. With this, you get 100% a Quadra Kill or even a Penta.

Standard Katarina build starts with Dark Seal. If you see that you are the dominator of the game, upgrade it to Mejai's Soulstealer for more extra AP. At your first back you need to buy stuff that will ensure you a attacking and a defensive start. As you can see, I have made a list for your first back (look at the start).

If you ban during the ban period, always ban Annie. She is the 1# Kata's counter champion. Also, Akali and Zed are also champs that can counter Kata, so, think carefully which one to ban.

Thank you a lot for choosing my guide, I hope I helped you.