Hi, I'm SecretRaindrop and this is my first Katarina guide, actually its my first guide ever. So if you find any flaws that should be changed plz tell me in the comments.
Now, i have played Katarina alot, and she is definitavly my favorite champion. she just fits to my playstyle. But i see so many katarina players out there playing with old builds, runes and masteries that no longer are viable on katarina...
So i decided to make this guide to help them and everybody that thinks kata seems like a fun champ.
plz dont vote before you have tested the build in a real game ;)

Pros: -Very mobile -High burst Dmg -Easy multi-kills with [Verosity] -Resourceless -Easy to towerdive

Cons: -Easily interupted ULT -low lvl 1 burst -No hard CC

So, after the preaseason update, and with these items the usual 21/9/0 arent that viable anymore, heres why:
the only things you get are 3% cdr, 5 AP and 8% magic pen.
While in the Utility tree you get slightly better roaming speed, about 25 sec. cooldown reduction on flash, and a very important 15% cooldown reduction on the tripple actives.

therefore we are going 0/21/9 now and this gives alot more tankyness earlygame and alot of utility late game.

The runes i have chosen on Katarina are not full AP like i have seen alot of other Katarina players do. They focus on high dmg with base stats, high magic resist and armor, and high movent speed. This gives you alot of opportuinities to outplay your opponents in lane and alot of stats that would cost alot of gold in items ingame.
It also helps you chase/escape with your movemnt speed + sinister steel. Countless of times when i have had a volibear after me and he uses rolling thunder i just sinister steel when he comes in range and run away from him, he wil catch up because of the steady high movement speed, but the low cooldown on W lets you do it again and again.

What the different abilities should be used for:
Bouncing Blades: applying marks to champions and minions so your abilities and basic attacks hurt more. Can also be used for lasthitting
Sinister Steel: harrasing, farming when compined with , lasthitting, escaping cuz of the 40% movement speed increase.
Shunpo:This should only be used for lasthitting if you are absolutely sure you are safe and arent going to get ganked within the next 10 secs. otherwise you can use it to get to your enemies, and away from them, the passive helps alot in fights. Can be used by advanced players to "ward hop" wich basicly gives you a free Flash.
Death Lotus: you can actually use this to harass your opponent in lane, tho it shoud be saved for killing them and teamfights. It applys a healing debuff wich is very usefull against champs like Swain and Vladmir.

You should prioritize lvl'ing up your sinister steel first because of the short cooldown compared to base dmg. this helps you farm easily mid/late as all you need is a + sinister steel to farm a minion wave.

Because of the long cooldown and low dmg on this should no longer be used as a spam harass spell, but we lvl it up 2'nd because of the mark it applies.

is basicly only utility now with the jump and damage reduction, therefore we max his last

As always take your Ult whenever you can.

There are a couple of combo's you should know about:
Farm: + sinister steel / + sinister steel +
Harass: + + sinister steel / + + sinister steel + + sinister steel
Escape: sinister steel + (use sinister steel on the champ chasing you if he is close)
Teamfights: + + sinister steel + + sinister steel , then just pick off kills with and sinister steel until you get cooldown reset and do it again

The first item set are buildt to make you deal high single target dmg and getting away/picking your next kill without getting bursted. It also gives you alot of sustain and some CC. you can change the item sequence after Hextech Revolver without much problems. E.g you could buy Chain Vest and/or Negatron Cloak after Hextech Revolver to gain high early game tankiness.

The second item set is if you are against a team with E.g 4 tanky champs + an AD carry. It gives you about the same amount of magic resist and armor and AP. but it gives you alot more HP, Magic pentration and slow on all ablities. this helps you doing steady dmg to your opponents instead of bursting them.

Your job in a team is to pick off stray champs from the enemy team and hop in and ult the enemy team in teamfights.
In lane when you have pushed it(its really easy to push your lane with katarina), you can easily gank top or top from lvl 3 and on. Because of your high mobility you can jump in from a bush and gank, maybe earn a kill/assist and be back without loosing to many lasthits and XP.

In Teamfights you should in the beginning stay behind your team and let them do the poking and initiating. When somoene has initiated AND you see most of their CC has been used up you can either go all in with the combo i mentioned earlier or run away based on the outcome of the initiate.

You should Primeraly lasthit with your basic attacks as to not push your lane and make yourself open for ganks.
If you are playing against a ranged AP carry with lots of poke you can stay in the back and let them push/harass them with , and when the minion wave arrives easily burst it with the farming combo i wrote about earlier.
Late game farming is like the easiest thing in the world, when roaming just easlily burst minionwaves in the lanes you walk past and earn lot of easy gold.

I hope you liked my guide, for you very first readers, im just saying it agian if you find something that should be changed/improved or that something is missing plz comment it in chat and i will do my best to fix it.
(still trying to learn the BB code so i can make the guide more interactive)