I'm honestly pretty new to the game and I have no idea why I'm making a build guide.
Hey, try new things? I guess.

Anyway, when i first started i found many champs that I liked, but one stood out the most.
You guessed it, Katarina.
Although I sucked at her at first (As many people do) I began to realize her strengths as well as weaknesses.(Although I'm still pretty bad at her, haha)
With the right items, runes, and mastery set, you can obliterate almost any enemy with a few presses of a button.
To be honest, I don't even know why I'm making a guide, because I'm still pretty bad at her. But better than when i first started I can assure you. This guide just comes from my experience with The Sinister Blade. (Fits her name very well)
Also my favorite skin is Bilgewater Katarina. 10/10.

This guide will not be very in depth. Only to help newer Katarina players, definitely not for pro's trying to learn new things.

Pros:
+High damage
+Manaless
+No skill shots
+Very mobile
+Multiple AOE abilities
+Ability resets
+Strong against skillshot champions

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Cons:
-Weak early game
-Most players (Sometimes even including your own team) will hate you for playing her. "No skill champ" although that may be true in some cases, we can all admit she's fun as hell.
-No built in CC
-Very weak against CC
-Squishy
-Focused on in team fights
-Has hard counters
-Hard to master

If your like me playing katarina, you want alllll the ****ing kills.
So this means medium amount of teamwork, and more kills.
And also kills.
Kills. Lots of them.
But that maybe just be me........
*Clears throat*

Now when you farm, you gotta make sure a champion isn't very near you. But if they are, press your q on either them, or a minion nearby them to hit them with some stabby stabs.

With her e she can:
Ward jump (Press e, then left click ward)
Minion jump (Same thing as ward jump, but with minons)
Ally jump (Same thing as said jumps only with ally champs)
And also a neat trick is, as I said in pro's and cons, she has ability reset. Which comes in VERY handy.
Such as, you e into the enemy team, use your r, then if you kill someone, your e resets. Which means, once you kill one person in lets say, a 1v4, WHILE still ulting, you can E to another champion to wipe them out as well.
You have to have fairly good reflexes for this, but it pays off SO much.

The most common combo is:
Q, E, R
Very good damage, and simple.

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For the next one:
Q, E, W

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And the last one (Ultimate damage)
Q, E, W, R
(Absolute rape to the enemy team, in big fights. Such as, 1v4, 1v3, or 1v5. with item build)

Well guys, this is as far as I'm going to go with this.
Constructive criticism is ALWAYS welcome.
This is my first guide actually, so I hope you enjoyed it, and it was helpful :)
Some of this guide was inspired by the "Blade of Noxus" build guide. Amazing guide.
Now get out there and **** some people up!