Hi, I am an AP mid player who primarly prefers assassin champions, especially katarina, i've been an avid Katarina player for quite some time now and i want to share my personal preference of how to play her. Keep in mind that you will excel by finding your own playstyle but here are some guidelines if you're looking to get started with this champion, i highly recommend modifying the build/playstyle of this champion to match your own preferences aswell.

http://tinypic.com/view.php?pic=2i7bgj6&s=6

Here are my current stats for Katarina in season 3.

I run 3 different runepages on Katarina, the things all those 3 have incommon is the quints and the marks, i use movement speed quints for added mobility in chasing enemies and roaming faster, it will also help you escape from junglers who can not gapclose on you effectively. You can run flat AP quints aswell, it will add a small amount of damage to your early harass however i choose not to use them since i value roaming and mobility higher throughout the game.

For glyphs i use ap/lvl or magic resist depending on how rough the lane is, if its a laner with strong burst and/or strong harass i will usually pick up the magic resists glyphs.

I pick up ap/lvl glyphs against lanes which i feel i can get away with it, dont be hesitant to stick with mr glyphs if you do not feel comfortable at all playing her yet, it helps you survive in lane and negate some harass damage.

For seals i usually go hp/lvl yellows since i prefer not to build health items at her most of the time so when i get my resistances i will still have some health to make them more efficient.

If i expect to face an opponent with alot of physical damage i will pick up my armor seals instead to negate their harass, it is vital in some matchups (pantheon etc) which can be quite brutal without armor during the laningphase.

I use magic penetration marks on every single Katarina runepage i own, its quite a nice bonus in magic penetration which will negate some of your opponents magic resist.

Level 1 95% of my games you will see me start boots and 3 potions the only times i stray from that opening is if im facing an extremely rough lane against a physical damage dealer that is looking to pressure me really hard in lane, in that case i will go cloth armor and 5 pots for extra armor and sustain in lane.
Boots
Health Potion
Cloth Armor


The first time i recall i buy different things depending on the matchup/gold i back out with/enemy heroes etc, its completely situational, the following are my most common though.
Sorcerer's Shoes
sight ward

This one is for the times you are backing off with 900 gold or more, pick up sorcerer's shoes to shred your opponents mr and gain additional mobility, pick up additional health potions if needed aswell and make sure to buy wards, wards are your best friends as katarina, if possible ALWAYS have atleast 1 ward on you after you have been shopping assuming you have the space to carry it on you, preferrably 2 wards. (further explanation about the wards in the tips & tricks section)

If you do not have enough gold to purchase every single item above i would advice you to just buy health potions and 2 wards, upgrade the shoes on your next trip home.

Negatron Cloak sight ward
buy this instead of sorcerer's shoes if you need it against your lane opponent (helps even more if they have a jungler who deals primarly magic damage). This is a more safe option which you will give up some early damage for in exchange for survivability in lane.

Elixir of Fortitude
You can buy one of these in combination with any of the 2 routes mentioned above, it will help you with a slight burst of health to bait your opponent into engaging you overestimating his burst against you and might give you a kill in when he has used his cooldowns, this is only optional and situational, but feel free to try it out, it has helped me out during some sick all ins which left me with next to no health left at all.

The rest of the game your item builds will differ from how the game is going & what you are facing.

Here are the items i will usually buy and my reasoning behind it.

Abyssal Mask
This item is a must have if the opponent is heavy on magic damage (AP champion top and AP champion mid for example) if they have alot of magic damage, buy it. It adds some MR shred for your team and yourself aswell while giving you a nice amount of AP. You can get this as your first major item but i would not recommend buying it much later, you can hold off buying it as your second major item at the latest in my opinion, i like it early as the MR shred will usually be more effective the earlier you complete it. (do not hesitate to buy it if they only have one with magic damage as long as he is big enough threat for you)

Deathfire Grasp
This item is great for roaming around and securing kills on single opponents, gives you alot of additional burst for the main target you want to kill fast in teamfights and has a nice chunk of AP on it to benefit your whole spell rotation.

The problem with rushing it is that it has a really expensive component and cost to complete the item which will leave your inventory blank for a while unless you back out with 1600 gold or more early, its viable getting as your first major item in some games if you can farm the needlessly large rod fast while not sitting around with nothing in your inventory for a long time.

in other words, do not complete this early unless you are doing well, and its still optional/situational.

Rabadon's Deathcap
This item is pretty much just boosting your entire spell rotation with tons of ap, which is excellent, pick this up when you need/want raw ap, works extremely well if you are far ahead in levels and farm and will help you demolish them completely in cases like that. If i am superfar ahead this is usually my first major item of choice since you will just beast through their entire team with it.

Zhonya's Hourglass
There is absolutely no game where this item would be a questionable pickup, EVER. I consider this item a must have on katarina in her full build. Get it when you have enough damage since it will help you stay alive a while if you are not getting a reset of your cooldowns when you first jump or you are getting focused hard.

If you build a rabadon's deathcap first this is what i recommend you following up with as your second major item, you will not regret it.

Quicksilver Sash
This is a situational item that you should pick up after getting some damage to avoid getting locked down by lots of hard CC and supressions (Malzahar ulti/skarner ulti etc)

Never get this as your first major item though.

Void Staff
When the enemy team begins to have a good amount of magic resistance late game this is item can be picked up

Never get this early though.

Guardian Angel
This item is great on Katarina, its basically a second chance at reseting on their team if you die while trying, in my 6 item build going into lategame, i will always have this among my goods. However you need damage before you start building a GA, if you're not a threat it does not matter if you live twice.

Here are some items i do not include in my build and my reasoning behind doing so.

Rylai's Crystal Scepter
This item provides a minor slow on your aoe spells and a good one on your E, My problem with it though is that it does not improve your ability to burst enemies down as quickly as the rest of the items and i do not feel that the utility the slows offer or the health is worth it, it will most oftenly not save you if you are getting focused either way and you're looking to kill your most important target on your first usage off your spells anyways, so the slow will usually not help you in doing so. Its not a horrible item on katarina but i think its inferior compared to the others mentioned above.

Some might argue that the slow from E might help you stick on them with your ultimate, usually if you do not kill someone with your spell rotations its because of CC or them flashing out right when you E them, not them running away. The slow your other spells offer is weak and not significant enough to get this item in my opinion.

Will of the Ancients This item provides some minor healing on Katarina however it heals less for area of effect damage, which is your biggest damage output. only your E provides you with the full healing amount. Its not horrible, it heals for an okay amount but i do not feel like its the most efficient item to get on Katarina.

Liandry's Torment Katarina is based so much on her AoE damage and this item actually gets weaker on spells like that, while it aswell gets more effective if their movement is impaired which Katarina is depending others to do for her, its not the most efficient choice in my opinion.

Hextech Gunblade Just like with the will of the ancients the spellvamp feels kind of underwhelming and while it grants a pretty nice burst of damage thats scales with your AP i prefer going deathfire grasp over it as it adds more damage overall on your target if you are looking for single target burst.

Okay here is a real question of preference, there are 2 good ways to level up Katarians spells right now.

This one focuses on you maxing Q for Safer harass in lane and slightly more upfront burst damage when you procc your mark. When you are using this skill order you are loosing the utility you get from maxing W which i will talk about more below.

This one focuses on you maxing your W for that massive movementspeed burst for a short duration and it actually gives you faster pushing in mid, riskier to harass with though as you have to get closer to them and is more often than not putting your E on cooldown if you are facing a ranged champion.

Try them both out and choose after preference, i switch between both but most oftenly use the max Q one. It is situational after lane aswell in many cases which i will talk about more in my matchups section.

Here i will try to give some tips for common matchups i face in mid as Katarina.

Kassadin

When you are facing a Kassadin, you SHOULD not be able not kill him, unless he majorly screwes up. He has a great kit against kata, his silence will abort your ulti so do not even try to ult him while he has that off cooldown. If his Q is on cooldown and you ult him he will R away, if he uses both of those and you can do so (safely) you can jump in and do your spell rotation (Q E W R) and punish him. This usually wont kill him unless he has taken alot of free damage since his passive gives him alot of resilence against you but it can force him out of lane, force him to play more passive which is benefitial for you.

The only advantage Kassadin doesnt have over Katarina in lane is pushing power, Katarina outpushes him greatly and you should abuse this as much as possible to force him to his turret. While there he will have a harder time csing and can not focus on harassin you or roaming without loosing farm, which will give you a headstart should you find a opportunity to roam while he is busy cleaning up your creeps.

Basically you are not looking to kill him in lane, it wont happen, unless he misplays alot. You are looking to outfarm and outroam him.

In teamfights you should try to not be vulnerable to his silence, if you have to wait until its on cooldown, then wait. you wont do anything if you allow him to silence you once you E into their team anyway, you just made yourself vulnerable instead. (this is true for most of the cc when playing Katarina but kassadins silence is one that really screws you over, not only interupting your ulti but its duration is long enough to set you up for further cc or kill you)

Do not have him as a first target either, unless its a for sure quick kill and he is like 20% health when you go on him, you can not take him out by yourself unless you are ridiculuosly fed.

Ahri
Ahri is actually a fairly good pick against Katarina, but both can outplay eachother in lane.
Basically you want to punish her as soon as one of the following things happen
-She manages her mana poorly and runs out of mana
-She misses her E while trying to harass you
-You can force her ulti while surviving the aftermath (do not forget to keep track of their jungler while doing this, its a super risky move that you only want to do when you can get out alive) Its more benefitial if you manage to trade your ulti for hers since she is more vulnerable without it and yours is on a shorter cooldown.

Basically its up to ahri to loose this matchup, the more stuff she hits and the more conservative she is with her E the worse the lane will be for you, if she randomly throws it around make her regret it. Be careful for her Ulti all in on you once you go around 60-70% hp you wont escape if she hits her stuff.

Swain
If the swain player is good he will punish you so hard early levels, you can not retaliate his punishment, farm with Q, miss CS if you would take to much damage going for it. NEVER use your E on swain during the early laningphase against him that means you just opened up yourself for a snare and lost most of your health, even if his snare is on cooldown he will punish you hard for it with his superior damage early.

This lane i would just try to farm early and roam if possible, he wont be that big of a problem later but in the start of the game he has the potential to give you a really hard time. (negatron cloak highly recommended)

Cho'gath
This is the absolute worst midlaner for Katarina to face ever, whenever i see a mid cho gath on the enemy team im just disgusted.

Okay so you got a cho gath in mid against you here is how the lane is going to go

-You can not harass him
-You can not kill him
-You can not outpush him

Only farm and roam when facing a cho gath, do not even think about harassing him, he will just heal it up just as fast as he took damage. Be careful aswell, if he catches you he has a good burst and a big part of it is true damage so you will not be able to negate it other than health, which will put your damage output behind.

Orianna
Orianna has quite nice pressure against Katarina, her enhanced autoattacks and ball can bully you in lane if she is good at handling it however you can take advantage of her missing her ball and jump in on her and punish her abit, this lane is all about if orianna can use her ball effectively and outpush your properly since you should not be able to push the wave before her (if you walk up for a W she will for sure try to punish you for that)

Basically evade her harass and retaliate if you will come out ahead, and keep up in farm, she can punish your roaming by pushing the wave before you, if you sacrifice the farm for roaming and not picking up a kill you will eventually fall behind, play wisely.

Cassiopeia

Brutal harass once she lands a poison and gets in E on you, possibilites for outplaying her with E if you can predict her ult and make her miss it (you will appear behind her) or when she fails to apply poisons to you or even worse, uses E when you are not poisoned, if those things happen, punish her for it.

Morgana
Pretty straightforward matchup, you are not dying against her unless you mess up, avoid getting snared and match her push, keep E of cooldowns in case of her ulting you.

This matchup should not be problematic.

Lux
When facing lux she will hurt if she hits her stuff & her autos on you while you are debuffed, however you can punish her if she uses her q poorly, its a free jump for you as long as you know the jungler is not there (wards/check map if hes on another lane and so on)

Malzahar
Ok this guy is obnoxious, i typically will just farm and roam when playing against malz, and get a neg cloak to negate harass and prevent him going all in on me with ultimate, beware of his jungler coming in combination with his ult, ward so you are aware of it.

Diana
You can punish her before level 6 by maxing Q and constantly poking her, evade her Q's as much as you can and just keep poking, forcing her to blow all her sustain or shield with mana, either way she is going to loose resources, i recommend negatron cloak in this lane, keep your ulti off cooldowns as long as her E is off cooldown, dont let her get free Q R combos on you and farm this lane, you can outplay her if she does mistakes but she has the advantage as soon as she hits 6.

Pantheon
When facing a pantheon, buy cloth armor and 5 health potions since you will recieve alot of harass, you will not win trading damage with him so just farm and roam, you can outpush him the later levels of the laningphase. (you will outscale him as long as you get your farm so no need to feel pressured to get far ahead of him, if you both go even its good for you)

Sion
This is a hard lane for katarina which will be picked mostly just to screw your laningphase over, just as with pantheon you will outscale him if you are both even so get the farm you can get and play safe.

When he activates his shield do not open up yourself for a stun even if that means missing a minion kill. You will not outpush him since he can punish you going near the creepwave with his shield harass, his laning harass and burst is strong in the laningphase so i suggest buying a negatron cloak to survive it. As with pantheon you will not win any early damage exchanges against him.

Karthus
Karthus is not hard to deal with during the laningphase as katarina as long as there is no jungler nearby you can punish him, i usually max Q this lane and poke him and going aggressive with my E W aswell, if he slows you thats the only time he should ever catch you out with a Q, which he most likely will do to countermeasure your harass when you are backing off.

Try to predict his wall and dodge it otherwise dodge Q's the best you can or stand next to minions to reduce the damage taken, he should not damage you severely enough to get you killed if doing this. You can punish him alot during the laningphase as long as the jungler is not a threat to you.
He will outscale you though if he farms good but other than that you will have every other advantage against him.

Use your R alot even it means not killing him but sending him back to base, and deny creeps by pushing it, when you get ahead you will usually get him killed by harassing and going all in with your R

Usually the karthus will bring an exhaust to this lane, which will be used defensively most of the time, at the best it saves him when off cooldown, never had problems laning against a karthus, its the best matchup for katarina in my opinion.

Twisted Fate
An extremely good TF player can be somewhat threatening but they are rare, TF excels at pushing fast in lane with his cards and then roaming with his ulti, you can ward your midlane in the middle of the lane right out of his tower range that detects your ward to see which direction he is heading and warn your lane for his arrival, you will not be able to follow him fast enough, so push his tower as much as possible should he decide to ultimate to a lane.

If he uses his card on creeps you have an opportunity to go in on him and punish him, quite alot of twisted fates use their cards unwisely and that is your prime opportunity to get in harass, if you jump on him while his card is off cooldown he will gold card you and follow up with wild cards and some autos which will make the trade less benefitial for you, especially if he gets a E procc on that aswell. you can max Q and poke him in lane aswell as long as he do not have a card drawn.

Leblanc
Leblanc has a huge advantage in terms of early damage and an easy time silencing, she has really poor pushing power however so get a negatron cloak in this lane and outpush her and outroam her.

Do not underestimate her early damage and harass and this lane should be pretty easy to handle once you get a negatron cloak, there is only so much she can do against you if she is pushed up against her tower the entire laningphase. I would not recommend going all in or trading too much with her unless you are ahead and will win that trade/all in.

Brand
The only time you should ever use your E on a brand is if he misses his stuff, he outdamages and outtrades you early so only take advantage of him using his skills or mana poorly and runs out of mana, you can Q poke him behind creeps (preferrably with minions behind you to evade his W with your E)

If he maxes E just to mess with you and starts spamming it and autoattacking, just play conservative and do not open yourself up for too much damage as it can make you blow all your health potions early, this also means he will be vulnerable to jungle ganks if he goes deep in the lane.

Fiddlesticks
He is like a less threatening version of cho gath, you will not be able to harass him effectively because of his healing and you can not kill him because of his CC (unless he uses it really poorly and puts himself in a horrible position) He will typically harass you with his silence and or fearing you into a life drain which forces you to run away so even though you have better push than him it can be problematic actually pushing since he will force you off the wave alot.

When playing against a fiddlesticks on the enemy team i usually pick up a negatron cloak and turn it into a quicksilver sash later in the game, to stop his massive fear.

You are pretty much relying on farming and roaming in this matchup, it is not that hard to stay even in farm however it can be complicated actually getting the way pushed for your roaming if he punishes you for it, try asking for help from your jungler if he is constantly stand ahead of his wave waiting for you to clear it.

Annie

Annie has a really strong burst potential and you should avoiding trading with her if she is able to retaliate with her passive stun. she has a really long auto attack range aswell which will edge in some more damage to top it off, get a negatron cloak this matchup for sure since her harass and all in will be highly problematic without it. you can outpush her if you manage to not get punished to hard by her in doing so, she usually wants so have a stun ready so she will be conservative with her spells most of the time, forcing her to blow her W stun on creeps to counter your push will force her to stard building up charges again, i would not recommend going aggressive that much in this matchup since she will outdamage you.

Anivia
Anivia has huge pushing problems pre 6 and you should do whatever in your power to abuse this, do not focus on harassing her with E since it will put you in a good position for you to Q + E you, just focus on pushing and use your E to dodge her Q, she will be pushed to tower with a harder time lasthitting until she hits 6 if doing so, giving you a free opportunity to help your jungler to counterjungle or defend your own jungler or roam early if an opportunity arises.

after 6 this lane becomes worse, she is hard to kill aswell as most anivias i face go chalice and catalyst which will give her alot of mana and health & mr to withstand your early damage, she will outpush you after 6 aswell and her R + E combos will hurt if you let her get them in, i usually do not go negatron cloak in this matchup though since i usually get away with sorcerer's shoes and something offensive after that instead. just focus on farming and roaming after level 6 if you are not ahead enough to come out on top in trades.

Vladimir

Before he hits like 7-9 and gets his hextech you can actually trade damage with him and come out ahead if you wait for him to use E or Q on creeps to push faster (you will outpush him as long as his E is not maxed, which no vladimir ever skills up first) if he saves them to counter your harass or harass you, just push him to his turret instead.

Once he gets his hextech he will be extremely hard to harass down low enough so keep pushing and forcing him to turret until his E is leveled up enough to counter you doing so, and roam if possible while he is stuck at his tower.

once he can push at the same rate as you its a farmlane for you, just farm unless you are ahead enough from your early game to beat him down.

Zyra
Zyra has some really nice damage potential however she relies on you casting your E before she should ever be able to punish you with it, hence if she decides to use her stuff first just punish her by using your E and rotation on her, be aware of jungler when doing this as always.

If she however only uses her Q and plants to harass, judge if its appropriate to go in while she still has her E up. Just farm and punish her if she tries to use her snare on you.

Her ultimate is not a problem regarding your ultimate since the delay on it before snapping is long enough for you to channel your ultimate.

Mordekaiser
This is a fairly rough lane since his passive will make him very hard to trade with effectively and hes has really good pushing power, try to farm during this lane and roam since your roam is far superior to his. Negatron is optional if you find his harass strong enough to buy it. (i usually run MR glyphs against this matchup)


Galio
When facing a galio, out push him early since he can not keep up until he has his chalice without dropping all of his mana, you can punish him aswell if he uses his spells to push early levels or misses them. Force as much mana as you can before he has the chalice and freeze the lane close to your tower if possible and punish him hard for ever trying to get near it, once he has his chalice and his ultimate its basically you cleaning up his pushed wave and getting farm, your not getting any kills or pressure on him once he has his needed supply of mana.

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Do note that sometimes your opponent will be making bad plays or be really far behind for various reasons if then you can punish them more than just farming and roaming, the farm roam is pretty much your autopilot mindset when they are not making mistakes for you to be able to punish them.

How do you know if you want to trade damage/punish your lane opponent?
Depends, here are the things i keep in mind when deciding if its appropriate.

-What is on cooldown on the enemy? Will i benefit more from going agressive?

-Can the jungler be there? If yes, will i die if i Use my E on the enemy? (you can ignore jungle pressure from weak early junglers such as warwick pre 6, malphite pre 6, if you have flash up you can use your E agressively until they hit their prime)

-Do they have a shen or nocturne? if yes then do not all in unless their ultimate is on cooldown or you have a flash up and you are confident you can flash out if shen ults etc, calculate the risks and prepare a countermeasure if things go wrong before they do.

- Ward one side, in midlane atleast. stay close to that side since its safe, they should not be able to gank you if you hug a warded side (exceptions for flash ults which you will have to account for when you decide how far out you want to step on your lane)

- You can use your E to jump on wards, i try to keep one at me as a reserve always as a escape tool, practice until you can do it fast enough.

-If you have to choose between taking a long way when roaming/coming back from a roam or checking a brush head on when enemies are out of your sight, always pick the long way.

-Many games i've dominated early as Katarina because of roaming and snowballing that way even against hard lanes, if you cannot kill your lane opponent find different ways to get ahead.

-Be aware of what CC is up and not up when going in a teamfight, unless you have a clear kill on a extremely dangerous target but one that will probably cost your life (example: fed ad carry lategame, you can sacrifice your own life for that if you can ensure that you will get him)
Otherwise play safe and do not engage, you do not want to attract any attention or CC.

-When ganking a lane with a stun walk towards them and Q + W, hold on to your E & R until stun is used, proceed to catch up with E and R when they use it on you.

Flash + E is a extremely lethal combo since your opponents (ad carrys in teamfights) or people overstaying when they shouldnt in lanes but far back can net you some kills on unexpecting opponents, do not only use it as an escape.

(this can backfire if they are baiting and the jungler is waiting behind the tower, be careful, its a high risk move and should not be done if you are far ahead and might risk giving up a killing spree for that flash + e)

- If several opponents are on 10% life and its no longer about damage but speed on which you have to kill them before they scatter, use E + W if you are _sure_ it will kill them, since Q has a short cast time it will speed up the resets slightly which can be the difference between one getting away or not. (its extremely uncommon that i would find it usable to skip my Q but it has happened)

- Try getting used to smartcast when playing katarina, it helps wardjumping with your E and reseting your skills on champions at a quicker rate.