I people. Im here just to make a promise. I will not full your mind of the same thing you have just seen a minute ago on another guide here. I want to show you a lot of shape of this champ.

This chaamp is not a Killer. She can be Wing or can be Iron.
Is up to you choose what u want to build and what u want to do with this champ.
This Champ is:

Assassin: well....you already know this....
Tank: Katarina can be a real tank with real tank stats and still kill a lot.
Split pusher: Lot of Item grant you a lot of split pushing Potential.
Bruiser: Why trust a 0/5 Kayn when you can do the first move and hope to your iron 5 teammates to join the fight?

I will be more than honest. COnqueror and Dark Harvest are the best rune for Katarina on every matchup and on every item path.
Later you will ask yourself about some other rune mechanics.

I will answer to you: Basically almost every rune run well and clean with Katarina.
From grasp,phase rush and electrocute to conqueror, dark harvest, arcanecomet and omnistone.

With Katarina you can try every combination of rune, and they will eventually work (more or less). So unleash ur fantasy and try every rune path (yes, even press the attack work well on kitty kat).

This Item are just the same of what u can find everywhere. Im not here for this!!

Katarina is a great split pusher in this season 11. U can abuse this to become a little more like a yasuo main....

Based on your build, you can choose what to do.

Split pusher: let those Iron 4 do an Aram midlane and abuse of that moment to take down objective on top and botlane.

Assassin: your Malphite engage in a teamfight 1v5? You just press E in the crowd and then ult everybody.

Tanky: Basically you will do what Malphite does in the previous story but you stay on fight until your enemy are all dead or most of their stun are wasted. Then u just go away to chase the single target.

Katarina with just the Blade of Ruined King can do a solo drake early game.
If your jungler is near the drake, Ping that your coming too to kill him as fast as possible. Never trust your botlane. they are just good to feed Samira and tristana player. Your jungler and you are the only human in your team. The other are just ape that feed and int every lane phase.
Use careful the ward because you can avoid that your enemy mid laner get a kill early.

This Build is for the player that wanna shock their opponents like zed or talon.
They will deal more or less a Soraka Q damage to your katty.
Have fun on lane and try to change your build based on enemy and ally team.
DONT do the same build everytime or you will regret the late game of this champ.