Introduction
Hello this is my first guide and it is about my favourite champion Katarina. Hope you enjoy reading and learning from this guide along with playing. This is not the only way to play Katarina and you can always mix it with your playstyle. Don't take this champion lightly it requires skill and devotion as much as the other champions.
Skills
(Passive)Voracity: After a kill or an assist, Katarina gains 25 gold and her cooldowns are reduced by 15 seconds.
1-Bouncing Blade: Katarina throws a dagger that will bounce from enemy to enemy, dealing magic damage. Each subsequent hit deals 10% less damage. The blade won't bounce to hit the same enemy more than once on the same cast.(+) Attack Damage (0.8 Ratio) Ability Power (0.35 Ratio)
Level Up:
-Level 1: 60 DMG, No Cost
-Level 2: 95 DMG, No Cost
-Level 3: 130 DMG, No Cost
-Level 4: 165 DMG, No Cost
-Level 5: 200 DMG, No Cost
Range: 600

2-Killer Instincts:
(Passive): Each of Katarina's autoattacks and abilities will deal extra damage per hit. This gives extra damage to each of Bouncing Blade bounces and each of Death Lotus daggers.
(Active): Katarina's next basic ability has a bonus effect:
Bouncing Blade: Deals full damage to every target it hits and applies 50% healing reduction for 5 seconds.
Shunpo: Katarina takes reduced damage from enemy attacks for 3 seconds.
Level Up:
-Level 1: Passive: 8 Bonus DMG, Active: 15% DMG Reduction, No Cost
-Level 2: Passive: 12 Bonus DMG, Active: 20% DMG Reduction, No Cost
-Level 3: Passive: 16 Bonus DMG, Active: 25% DMG Reduction, No Cost
-Level 4: Passive: 20 Bonus DMG, Active: 30% DMG Reduction, No Cost
-Level 5: Passive: 24 Bonus DMG, Active: 35% DMG Reduction, No Cost

3-Shunpo: Katarina moves to her target's location. If the target is an enemy, she deals magic damage to the target.(+) Ability Power (0.75 Ratio)
Level Up:
-Level 1: 80 DMG, No Cost
-Level 2: 120 DMG, No Cost
-Level 3: 160 DMG, No Cost
-Level 4: 200 DMG, No Cost
-Level 5: 240 DMG, No Cost
Range: 700

4-Death Lotus: Katarina channels for 3 seconds, throwing 30 daggers over the duration to the 3 closest enemy champions in a nearby area around her. Each enemy champion can be hit by a maximum of 10 daggers.(+) Attack Damage (0.5 Ration) Ability Power (0.25 Ratio)
Level Up:
-Level 1: 50 DMG, Channeling
-Level 2: 65 DMG, Channeling
-Level 3: 80 DMG, Channeling
Pros / Cons
Pros:
- No Mana
- Easy to Master
- Great Ganker
- Amazing Ultimate
- Hot and Sexy
- Good mid-late game farmer
Cons:
- Gets focused a lot
Masteries

I play 21 points on Offensive because i want to get the AP,CDR and Magic Penetration that it gives. I play 5 points on Defense for the magic resist and the armor so i won't be able to do die so easily. And the final 4 points i play them on the Utility tree for the reduced time spent dead and to improve my flash spell.
Runes

I get the magic penetration runes because both her shunpo and bouncing blades benefits from it. I get the health runes so i can have a bit more health and so i can survive a bit more. And finally i get the ability power runes because Katarina is hero that plays with ability power and she needs as much as she can get.
Summoner Spells
Flash: For me flash is the best summoner spell for Katarina because along with shumpo it's like having two flashes. Imagine chasing a fleeing enemy champion that is not in the range of your shunpo. You simply flash closer to him and then boom you kill him with shunpo.
Ignite: I get ignite because it helps me with the damage. And whenever it is on cooldown i get 10 more ability power and damage.
Exhaust: Exhaust is a really nice spell for fleeing or slowing an enemy champion. If the enemy champion doesn't got stun you get to him with shunpo then you put exhaust on him and you tear him apart with your ultimate.It is good for fleeing too.
Ghost: Ghost is another good summoner spell for katarina. You can use with the same way as you could use flash and shunpo while chasing a fleeing enemy champion or when you are trying to run away to save yourself.
Laning
Who you want to lane against (solo):
Squishy chars:
Ashe, Warwick ,Teemo, Twitch, Yi, Karthus, Cho'Gath (early game), or any other, non high DMG char.
Who NOT to lane against Disablers:
Ex: Ryze, Fiddlesticks, Heimerdinger (his turrets will dominate you), Annie (even thought she is very squishy), Chogath (he is very easy until level 6 when he gets his ultimate and starts feasting), Mortekaiser (I hate lane against Morde his shield wastes my shunpo)
Who to lane with:
Stuns/Disablers: Fiddlesticks, Twisted Fate, Ryze, Malphite, Cho'Gath, Shaco, Nasus (that slow is killer)
Who not to lane with:
DPS/Casters: Twitch, Teemo, Yi, Tryndamere (in most cases), Gangplank, Anivia.