I've seen quite a few people giving out suggestions for Katarina builds, and it never ceases to amaze me how many people don't understand the premise of the hero. Simply put, Katarina is meant to be AP, and here is why. As with my previous guides, I don't intend on talking about the mechanics of Katarina and expect the reader to know the gist of the hero.

Masteries: 21/0/9: Katarina is a mobile nuker and built around cooldowns rather then mana. Rather then wasting gold on items that don't fit her, you should be utilizing the golem as much as possible.

Runes: Spell Penetration and Vitality

Leveling: It is very dependent on the way whoever you are laning up against acts. Kat truly shines in mid when her opponent is afraid of her. I almost always take shunpo at level 1 and immediately begin hit and run. Wait for Shunpo to cooldown, and repeat, and study the way they react. Some people run away, which is great for you, and some people fight back, which can be tricky depending on who you are fighting. Does your opponent out damage you? If so, take a level of ki and shunpo in with that for the damage reduc (That destroys mages.) Also, check for regen. A lot of players run things like dagger or lifesteal which is a total death sentence because you can harrass the **** out of them while remaining safe yourself with the item build I propose.

I generally run this..

1: Shunpo
2: Ki or Blades
Then you follow the process of Shunpo / Blades / Shunpo / Blades throwing in death lotus whenever you can. Despite what some think, Ki shouldn't really take a total focus over your damage.

Summoner Spells:

Without a doubt, Cleanse and Exhaust. Cleanse makes it so easy to bait foolish Ashe's or to juke out of a TF stun in early game, and an extremely awesome "Oh ****" button or an amazing way to get someone who is just out of your reach due to a slow/stun. Exhaust because the only thing that Katarina really needs to perfect herself is a bit of control to keep people in her Lotus grasp.

Items:AP. AP. AP!!! So many people go AD and completely miss the entire idea of what Kat is about. An AD kat Shunpos in and has to hit for a few moments where as an AP Kat shunpos in and takes down an Ashe in 1 second before she Shunpo's to safety. AP Is a needed tool to enforce the idea that Kat is a mobile nuker. During a teamfight, you leap all over the place doing insane amounts of damage. Let me paint you the picture of a typical fight for an AP kat that an AD Kat could never pull off for reasons that I'm happy to explain. Katarina is a MOBILE NUKER. You should be bouncing all over the place for the entire fight. I've seen to many AD Kat's shunpo in and then after their Lotus is over they are pathetic and useless and roam around being free kills where as an AP Kat has the burst damage required to turn a Team fight around.

An Ashe lurks in the back of a teamfight that Katarina hasn't yet entered. You shunpo/bb in and, as AP kat, literally take half of Ashe's HP followed by a BB. Ashe will die in 1-3 seconds flat, where as with Katarina, shunpo is simply a means of getting close to her, followed by the meager bb and THEN the real damage begins with your lotus. The thing about Katarina is that you don't want to give your enemies a chance to react. People talk about sustained damage with her which baffles me because why would you talk about sustained damage with someone so squishy that they are one CC away from being dead. Katarina relies on burst. With Katarina it's not about who is the biggest threat to the team, but who dies the quickest because of her insanely amazing passive. The second Ashe is dead, you have a free shunpo out to safety or you can continue delivering nearly equal burst to whoever has the least HP. Since you completely obliterate anyone who isn't a tank, and seeing as you targetted whoever has the least HP, you just killed them as well, thus giving you 30 seconds off of your cooldown on an ult that is already 45 seconds.

People say her sustained damage > Burst damage which is just insanity due to the fact that you can down a squishy in literally 2 seconds and then follow up with another 600 damage on someone and an ult that works like Fiddlestick's ult on steroids. Triple kills become the norm as AP Katarina.

As for the build itself...

Doran's Shield + 1 HP Pot. Doran's Shield is an amazing item that gives you the needed regen and armor to withstand your opponents harassment. I've seen many TFs and Ashe's go Lifesteal or something as silly as a single sapphire crystal which is so stupid because anyone who is decent at harassment and lane control will let you stupidly auto attack until the creeps are bordering your tower and then anytime they step even slightly close to the creeps you shunpo in and wreck another chunk of their HP. A well played Kat will often get first blood simply because people can't counter her early game harassment without changing their builds around.

My second trip back I get Sorc Boots or (Rarely) Merc treads. I don't see much of a point in anti CC when I run cleanse and I don't really stick around long enough to be targeted by stuns seeing as I don't have to rely on auto attacking for kills like AD Kat's.

I then get Zhonya's Ring. The new ring is so awesome for Kat in mid game because it boosts her AP above 100 and the protection it gives you is amazing if a gank goes awry because it lets you sit long enough to get your shunpo back so you can A.) Burst them again or B.) Shunpo to safety. It saves my life on multiple accounts.

I then get a Rylai's Sceptor. A perfect item that gives Kat a bit of a slower mentality and it works in amazing synergy with her Death Lotus as an AoE pseudo exhaust.

After that I tend to run Void Staff followed by Abyssal Sceptor for a bit of protection and the stacked magic penetration (Resistance debuff.)

If the game continues at this point I usually sell my Doran's Shield and get Nashor's tooth due to purely preference.

Items you should never get: Soulstealer or any of those other charged based items. They are snowball items and overly risky, not to mention a waste of money as all they do is offer AP and little else in way.