Well, basically this is my build for katarina ... I look the other builds, and they not really fit my style, so I decided to make my own guide, some items are weird, and others are situational, so, look items description to more details
The build is not perfect, i know, is completely open to change and constructive comments, if you dont like, dont vote negative without a comment, it helps improve the guide.
The guide is not complet, of course, i will add more details in time and change the guide if riot make changes, i will add tutorial videos too when i have time.
And well, english is not my main language, so i can have mystakes ... feel free to correct me
Last update : 19/11/2011

PROS
- Tons of damage
- NO MANA
- Very low cooldowns
- Multi target ulti and Q
- A flash skill Shunpo
- Easy to play
- Can make a game alone if the user is good
- Can take all lanes
- Good chasing
- Increible gank potential
- Can take very different builds, and it stills viable
- Your ulti can hit and detect invisibles
- Chain of deaths with your passive
- And well... it's a hot girl

CONS
- You will get focused
- Exhaust and you are down
- Very ulti dependant
- High expectations for kata players
- CC vulnerable
- Bad farm
- Bad early game
- Not a good jungler
- Need good reflexes to play and really shine in a game
- Can be avoid with a flash

The passive of katarina, the thing that distinguishes a good katarina,of a pro one, 25 more gold for each kill or ***itance, you can get feed faster, and will get you items sooner, and when you kill someone, the cooldown of all your skills are reduced 15 seconds, what means that? you can use your Bouncing Blades, your Preparation and your Shunpo another time, that allows you a chain of deaths. One of the best passives of the game, if not the best


The skill i maximize first, use it to get last hit of minions, if the enemy is near the minions, it can be hit too, that allows you to make constant damage

I get Preparation at level 3, when activated, change the effect of the bouncing blad and Shunpo, that allows you to make combo(look below section)


Amazing skill, very versatile, for both scape and chase, you can jump to the enemy target to deal damage, you can jump to a teammate or minion to scape, and the best part, you can even Shunpo to visors, you can have in the inventory a visor all the time, so you can put the visor, jump to them, and scape safely, combined with Voracity, allows you to make a chain of deaths


Kata's ulti, deals TONS of damage to 3 nearly enemys, a channeled ulti, it can be stopped with any stun or silence, if you know they will stop your ulti, dont use it, you are very ulti dependant so, dont waste it for nothing, most of the times, if they stop your ulti in a teamfight, you are death

This is what makes katarina, you have to learn when and why make that combos, otherwise you will fail.

Preparation + Bouncing Blades = All targets will have the same damage, and heal effects are reduced 50%, good for enemys that use potions, or if they can heal

Preparation + Shunpo = Gives you a damage reduction of 15% of ALL damage for 3 seconds, that gives you a lot more of survivability, you can even towerdive with this(don't do this at lvl 3 xD)

Preparation + Bouncing Blades to a minion + Shunpo to a minion or ally = All targets will have the same damage, and heal effects are reduced 50%, you deal damage with that, and then turn back to a minion or ally so, you won't take damage, repeating this will kill the enemy or make him back, a lame combo

Preparation + Shunpo + Death Lotus = The main combo of a katarina, gives you the 15% damage reduction and if you have Hextech Revolver, it makes you a hard target to take down

A lot of people maximize Shunpo first, and then get the Bouncing Blades, but i dont like this, Shunpo do more damage to a single target, i wont discuss that, but Bouncing Blades gives you more farming and pushing potential, and constantly do damage to the enemy if he stays with the minions, and a lot of people take Preparation at lvl 13, but i take it at 3, why? that 15% reduction in early game helps, and can get you the first blood more easily, and with Bouncing Blades + Preparation you can nullify enemy potions and heals, and it's completely effective vs a vladimir or an akali
and of course, Death Lotus as soon as possibe, in most of the cases, you are nothing without ulti

Not much to say about masteries, 21/9 configuration, get all ap masteries in ofensive, and armor, m. res and life for defensive tree, i personally prefer more damage instead of more survability.

Some people take 9/21 masteries, and its good too, gives you more survability

Both configurations are good, feel free to try both of them

Why i never put points on utility tree? Simple, you dont have mana, you have spell drain on utility tree, but i wont sacrifice ap, or more defense for just that

Greater Mark of Magic Penetration
Not much to say, all her skills deal magic damage, and you want magic penetration, like all the casters

Greater Quintessence of Health
Why this and not ap quinta? both are viable, you can mix them, but i get fortitude because you are going to be focused... always, it gives a bit more survivability in early game (you need it) and 5 ap more for each quinta is not really a big change, but if you like more the ap, go for it, it's good too

Greater Glyph of Cooldown Reduction Greater Glyph of Scaling Cooldown Reduction
Cd glyph reduction, it really helps, why i mix them? i get a bit more cd reduction at early, and a bit more at late, you can get full celerity for a better late or full focus for a better early, but i like more have both of them (it's not a big difference after all)


Greater Seal of Vitality
Same reason as the quintas, at late game, when you make your ulti in a teamfight, you are going to be focused, 175 life more at lvl 18 can save your life, or have more time to deal damage with your ulti, so your teammates can finish the job, and that hp have a better effect combined with Preparation, of course

RECOMMENDED


I love that spell, you can scape jumping walls, combined with your [shunpo] it gives you a terrible range and a surprise atack that usually gives you a kill, (or more), or you can jump a wall and enter a teamfight with your ulti... they dont expect that and can make your game.
You need flash for katarina, it helps A LOT, for everything... i can't imagine a katarina with no flash

My second favourite spell for katarina, ignite don't stop your ulti, so they can't heal a lot
when you are in your ulti and ignite them.
Or for example, you make your combo vs 2 enemies, and they both are going to scape with minimal health in different ways... ignite one, shunpo other.
You can live with no ignite, but i think it's really usefull

GOOD SPELLS

That annoying trynda with ulti gets useless with exhaust, good for chase, for take stronger enemies down, or when you make your ulti, Exhaust and they are gone, they cant scape
It's definately a good spell for katarina, you can use it and its very viable, recommended in some cases, i prefer the other ones, but feel free to use it



Really? heal? Yes, it can help for katarina begginers, to keep you alive when you are doing ulti, to heal teammates, or to surprise enemies, people say it's a noob spell, but it's very viable for katarina, i still prefer the other spells, so i never use heal anymore


Getting CCed? You are going to enjoy it, it's very good for katarina, but with my buid I use Quicksilver Sash, thats why i dont need Cleanse, if you dont like to use 1 item spot for the Quicksilver Sash, you can get Cleanse, the choice is yours


Well, usefull for ganks, to scape, to get faster into a teamfight... Take it if you like it, is a good spell, but i don't recommend it



NOT GOOD SPELLS


Simply not, you dont need it with flash, it can be usefull for escape or to get enemys in range, but thats why you have flash... don't take it for katarina


Katarina don't have mana, remember? Completely useless


Only for junglers, and you are not a effective one


NO
Too long cooldown just to revive, if you are doing a good job, you wont die enough to make it viable, it's just wasting a spell


Usefull, but let support take it, you need other spells to shine

Here goes the best part of the guide, or the extensive one xD
A lot of build are viable for katarina, but these are the ones that i use it, and the best ones for me.

Standard build:

The build i use in most of the games, with good effects, why i priorize the rabbadon's deathcap instead of the Rylai's Crystal Scepter ?
Most people priorize the Rylai's Crystal Scepter as the first major item, and is good, the passive combined with your ulti can do more damage than just ap, then why i take rabbadon's deathcap ? Burst damage, you need it, specially for the surprise atacks that i like so much,more harash potential... but really deppends on your style, so feel free to choose



i will discuss each item

Offtank build(really?):


When you dont want to be that squishy

My old build:


The build i used to play, but they nerfed the hextech gunblade, so i think will of the ancients is better now, it's a standard katarina build, and stills viable, you can play with it with a good results, you can see it lacks one item, this item deppend on the match

AD build:
(not yet)

And now, i will explain everything

VS
Very nice question, most of the people take cooldown boots, and other people take sorcerer's shoes, cooldown boots can help you A LOT, if you like that item, take it, whitout questions, BUT i still prefer sorcerer's shoes, why?


There is the answer, when you kill a champion, your three skills will be reset, unaffected with cooldown, thats why i priorize magic penetration, you will deal more damage, and if you kill a enemy, cooldown = 0, why you want cooldown if you can do that?
But if you cant exploit your passive, you have higher cooldowns, and that can cause you death... so, the decision is yours

Another point is, the marks, combined by masteries, and the sorcerer's boot with the Void Staff can lower the effect of a Void Staff, be carefull with that

Ok, now i will discuss all the possible items for katarina, the items i use, the items that can be good, etc

The mejai, katarina is one of the chars that can maximize the effect of a mejai, with the proper ganks and not dying, that can make you invincible, and enemys will surrender if you do a good job. But, is a snowball item, if you like it, and you are good with katarina, go for it, dont take it if you are a new player, never.


Already said, both boots are good, take what you prefer or fits more your playstyle

A very good item, gives a decent ap, and the spell drain you need, i usually get it as the first crafted item, you need that spell drain for heal yourself, and gives you more survivability in Death Lotus, get this item, always.

Nerfed item, gives 20% spell drain and 15% life steal, a good ap boost, and ad (your q, and ulti are hibrids, and heavily affected with ad), and the active is pretty good, because you don't have any cc, good for chase, and good for kill. This is a very decent item, and perfect for katarina.

So, if hextech gunblade is that perfect, why you choose will of the ancients? Till de nerf, will of the ancients have more spell drain(5% more) and the aura is pretty decent, but you only can have one, so if any of your team take this item, take hextech gunblade, no doubt about that

My first major buy in my standard build, a great burst of ap, you have to get that item on katarina, always, this item have no special pasive(except 30% more ap, that is insanely good), but really worths the cost.

The core item of a katarina, the passive is insanely good with all skills, you can chase with it, but it's specially good with Death Lotus, they will be slowed if they are in the range of the ulti, all the time, so they cant scape with no flash, the hp boost is good too, gives you more survibality, and the ap is good too. You need this item.

More normal defense, 100 ap more, and a passive that make you invulnerable 2 seconds... perfect item, dont you think? The worst part is, if you use your Death Lotus and then the hourglass, your Death Lotus will stop, but it give you a lot of survival potential, and can keep you alive most of the cases, why i don't take it? simply, is not my style... A very good item indeed, you can take it if you like it and the other team have a lot of AD.

Underestimated item, it gives you a decent magic defense, and the active is far better than a Cleanse, with a very lower cd, when you have to use it?
You are going to enter the teamfight, you active your Preparation and Shunpo to the enemy, and then you get stunned... use inmediatly a Quicksilver Sash and Death Lotus, you need good reflexes for that, all happens really fast. A very good item, and very cheap, i definetly recommend it.

Why not? Gives a decent ap, more magic defense and reduce magic defense of the enemys, is a good item if they have a lot of ap, but very situational

This item is VERY discussed for katarina, most of the people say it's useless for katarina, and in most of the cases, it is, but well, this item gives you more speed, you dont need it, but it's always welcome, gives a bit more of magic resistance, that is good for you, and a decent ap,it gives mana too... but that is useless.
If i say in most of the cases is useless why i take it? it's situational, the passive of this item helps you in a 1 vs 1... no more, no less, if you always go to teamfights , dont take this item, go for a Zhonya's Hourglass for example

If they are getting magic resist to counter you, take it, it gives you 40% magic penetration, it really helps if they are stacking magic resist, but useless if they dont.

ANOTHER ITEMS:

More ap and ad for each skill used, with this item, your ulti will get stronger and stronger with more time active, a decent item for katarina but it's very underestimated, feel free to test it, i personally prefer direct burst damage than gradually damage.

Very good item if they only have one way to stop you, gives you more magic resitance, and more life, a shame you dont need mana, but stills a good item

Some people take this item for katarina, but i can't understand why, it gives you atack speed that you don't need, mana reg that you don't need, etc... decent for a hybrid kat maybe... but don't take it


FIST ITEM ?


I see people take this with katarina as first item, but i think it's a mistake... gives you 100hp and 15 ap, the mana regen is useless for you, and well, the item can't be evolved into anything, if you want ap, take Amplifying Tome or bots of speed, is a better choice

Maybe the best doran item for katarina, more health, more ad( Bouncing Blades, Death Lotus)and 3% life steal... the best doran item for katarina, but i still prefer the Amplifying Tome or Boots

Recomended item for katarina in riot's build, but i don't think it's a good idea, gives you more health regen, that is good, just 10 more defense and of course, 100 hp more, but as i said, you can't evolve that item, better get Amplifying Tome or Boots

And now the big question, or

Gives you more damage, and enough money to buy 1 potion

bots of speed Gives you more speed, and enough money to buy a lot of potions

If you dont need life at all, get a Amplifying Tome if you need life, (going mid or solo top, for example) get Boots

You can farm in all lanes of the game, solo lane vs 1 or 2, mid lane or bot lane
The method to farm with katarina is Bouncing Blades to minions, last hit always and if the enemy use the skills and can't make you damage, shunpo them and go away.

I recommend mid lane, you will lvl up faster, get more money, and can gank top and bot lane

For top lane vs 2, i just recommend to last hit, stay behind the minions and the range of the enemies and wait for a gank

In bot lane, you can do a god job too(see partners section)

If you don't take a solo lane and go with a partner, tell them you need to farm(it's true) so, don't go with a carry if possible

The best lane partners:
Katarina+ Amumu
Awesome combination, amumu stuns the target and you Shunpo and Bouncing Blades to them, in teamfights make your ultis together... amumu + katarina = win, simple

Katarina+ Galio
Same as amumu, a strong combination and ultis are perfect together

Katarina+ Leona
Leona is a cc with legs, so is a good partner, and have AOE ulti, with a good synchronization is a winned lane

Katarina+ Alistar
Keeps enemys away, heals you and have a stun... perfect isn't it?


Well, there are the best ones, champions with stuns or CCs are good too

Bad ones:

Katarina+ Caitlyn| Katarina+ Ashe| Katarina+ Tristana
They need to farm, and you too, maybe strong combinations, but both of you will lack money in mid game, if you are forced to go with a carry, let him farm, and annoy enemys

Definitely not, never:

Katarina+ Janna
Don't do this at home, if you are not sync, Janna's ulti will take enemys out of your Death Lotus, Janna with you will be more an annoyance, but other supports are welcome

Your job in a teamfight is simple, Preparation + Shunpo + Death Lotus, never go first, let offtank or tank do this, if you go first, you are dead meat, even if you are feed
if you can use flash from a wall and enter the teamfight by surprise, you will make a lot more damage, pentakill maybe.
Usually they will expect you to Shunpo to the teamfight, and reserve a stun for you, sometimes is better to wait a fraction of second, and when you see the stun, use Quicksilver Sash or Cleanse and then Death Lotus

Don't jungle, katarina is not made for that

Blue buff: If no one of your team needs, get it, or kill the one that have it, that 20% CD reduction is very good for you, you dont need mana regeneration, let the mana dependants take it if they need it





Red buff: Let the carry take it, you dont need it, you have a Rylai's Crystal Scepter remember?





Baron: You need it, your team need it, and the enemy team need it, get it as fast as possible with no risks.

And that's basically the way i play katarina, all constructive comments are welcome, and questions too, this guide will have tons of grammer mistakes, english is not my main lenguage, feel free to correct

I will add some tutorial videos of katarina as soon as possible

List of updates:
19-11-2011 Guide created