Hello, I'm Haywyre. A Katarina one trick who has played Kat for around two and a half years now. My peak was D4 and have accumulated over 1 million mastery points on her across multiple accounts. I am ranked top 100 NA for Kat, peak rank 40.
Katarina is an extremely agile and bursty champion, with a high-risk high reward playstyle. She is super rewarding when played right and her kit is fully understood.

Pros – bursty, agile, great at team fighting, great at picking
Cons – squishy, very vulnerable to CC, high-risk, many bad matchups/susceptible to poke

Comps good with Kat:
Kat goes great with tanky comps with lots of cc and support, when your comp is tanky it opens opportunities to look for all ins, While the enemies are throwing their cc at the front line, you sit at the back and wait for the enemy to be either low or have little cc.

Comps bad with Kat:
[Work in progress]

Some fun syneries with duo partners or friends would be Ivern , Elise , Volibear , anything really works with Kat as long as it has good setup since Kat can't really set up ganks on her own.

Ignite and Flash will always be the standard for Katarina and Flash cannot be exchanged. Teleport is changeable for ignite but it highly not recommended unless you are top. Another situational spell set would be and , this is viable against matchups like mainly Twisted Fate, but is also okay against Ahri, or other hard CC matchups(I tend to only go this against Twisted Fate).

Doran's Shield or Long Sword are the only viable items to start as of patch 10.2. Doran's Shield against long ranged poke, and Long Sword against match ups killable at LVLs 1-3. Focus on finishing your Bilgewater Cutless and from there on you completing your Gunblade . Sorcs are the best bang for your buck as the magic penetration is great for it's price, especially when they already have a null-magic mantle. Zhonya's is the next buy after Gunblade and boots 90% of time as even if they have no AD or very little, it can help dodge major abilities such as ultimates or help with poisons and ignites (DO NOT, DO NOT, use your Zhonya's as a Tryndamere ultimate, use it to dodge the most damaging or longest CC ability). Morellonomicon is a crazy good item, it is usually the third item you complete after Zhoya's because of the health, magic penetration, and that sweet sweet ap, plus it's really good against Vladamir or champions that have lots of or build healing (applies grievous wounds passive for three seconds). Tank items are very good on Katarina, but only in very certain scenarios, full AP? Spirit Visage that ***** up, now you have increased healing by 30% and your Gunblade is aboutta pop off, Banshee's Veil is another great by because it gives ten extra more magic resist and a shield that cancel's out one ability every 40 seconds. Full AD? Sunfire has never let me down, I wish i could tell you why but honestly it's just a god tier items against all AD, give it a shot when you can.

For more in-depth looks on her build's, refer to the item builds further up.

Katarina's kit is very simple but comboing on her is very difficult, especially in high ELO.

Passive: Voracity
First Passive: Innate: Whenever an enemy champion dies within 3 seconds of Katarina damaging them, her abilities' Cooldown reduction icon cooldowns are reduced by 15 seconds.
Secondary Passive: Sinister Steel - Whenever Katarina retrieves a Dagger, she uses it to slash through all nearby enemies, dealing 68 − 240 (based on level) (+ 100% bonus AD) (+ 55 / 70 / 85 / 100% (based on level) AP) Magic damage magic damage and reducing Shunpo Shunpo's Cooldown reduction icon cooldown by 78 / 84 / 90 / 96% (based on level).
Daggers last 4 seconds before disappearing.

Q - Bouncing Blade - ACTIVE: Katarina throws a Dagger to the target enemy that bounces to up to 2 nearby enemies, dealing magic damage to each target.
MAGIC DAMAGE:
75 / 105 / 135 / 165 / 195 (+ 30% AP)
The Dagger then lands on the ground 350 units opposite from where it struck the target. The time to land from striking the target is the same regardless of distance traveled.

W - Preparation - ACTIVE: Katarina tosses a Dagger into the air above her current location, gaining a decaying bonus movement speed until it lands after 1.25 seconds

E - Shunpo - ACTIVE: After a short delay, Katarina Flash blinks to the target location around the target unit or Dagger, dealing magic damage to the nearest enemy in range.
MAGIC DAMAGE:
15 / 30 / 45 / 60 / 75 (+ 50% AD) (+ 25% AP)
Shunpo resets Katarina's basic attack timer.
Upon blinking, Katarina remains in Channeling for 0.15 seconds. Movement command buffering is also delayed by 0.85 seconds.

R - Death Lotus - ACTIVE: Katarina rapidly Channeling for 2.5 seconds, throwing a dagger every 0.166 seconds to up to 3 nearby enemy champions, dealing magic damage and applying Grievous Wounds for 3 seconds, reducing healing on the target by 60%.
MAGIC DAMAGE PER DAGGER:»
25 / 37.5 / 50 (+ 22% bonus AD) (+ 19% AP)
Katarina does not need to have Sight icon vision of the targets to hit them, and she will prioritize the closest ones.

In the early game, you have very strong power spikes you want to try to abuse and get before the enemy laner. You want to abuse level advantages and try not to die too much. If it's a losing matchup like Diana, you want to playback, roam when it's guaranteed a reward out of it. Spam ping laners and potential areas Diana might be in. So she doesn't get too high of a lead on you. Katarina's early game isn't too complicated, focus on getting Gunblade and boots and you're good to go.

Mid game is where Katarina starts so shine. If she's not behind, she can burst most people on the map, especially carries. Focus on taking objectives with your team and don't forget to soak as many waves as possible. You want to keep your lead or create one if you don't have one already. CS is extremely important, but most people forget about it after the early game. Try to pick off the viable targets, which means squishies, take out the squishies. That nearly your only job. Prioritize dragons and vision on Baron.

This is when you shine your brightest on Kat. You should have around 3 or 4 items by now and you're reaching your peak of the game. Team fighting is the main objective of this game, you're a team fight monster and should not be dying before team fights. Don't split alone recklessly, if you still have your lead take Baron when appropriate. Team fights you want to play passive in the beginning chose who you should be targeting and who is the lowest, focus on gaining your resets. A general team fight rule is go in when around the majority of the team is around or below half hp. Clean up from there and take the appropriate objectives.

Overall, Katarina is a great champion to one trick in season 10 and is a great solo queue champion. I suggest if you want more in-depth guides, check out Katlife on YouTube. He has many amazing videos from Katarina Combos to Katarina informative game-plays. Another person I'd like to recommend is Flyerbek, he helped me get a feel for an aggressive Katarina play style as Katlife's is more layed back and gaining leads gradually. I think both are amazing content creators and highly recommend them. Katevolved is KEKW. In all, hope you guys enjoyed my guide and I'll be updating every patch.

Feel free to check out my Twitch and Youtube while you're here. Although I am extremely inactive on those platforms, I will be returning soon when I figure out how to get above 100fps streaming and recording. Oh, also my Twitter I am quite active though.

Twitch: https://www.twitch.tv/project_haywyre
YouTube: https://www.youtube.com/channel/UCO3LMyuBZHtImvo6789QiHQ?view_as=subscriber
Twitter: https://twitter.com/HaywyreNA