This is simple guide.. I dont like guides when you must read for hours and you learn 2, 3 new things.. This is maybe for someone so bad and fail build, but try it once and you will see its pros..

Hello again, fellow summoners!

For those of you who had the chance to encounter the sinister blade in a battle and witness her might, leading you to a huge desire of buying her, I would like to recommend a build. This build is for those of you who just started playing as her or simply need an improvement in your current build. I will not discuss AD vs AP Katarina, I simply find AP far better, but note that if you are looking for a quality AD Katarina build or any AD Katarina build in the first place, this is not the post to look at.

AP Katarina seems to be the frequent choice of a few players I have encountered.

For runes, I am getting:

-Marks- Magic Penetration (Greater Mark of Insight) x9
-Seals- Armor (Greater Seal of Resilence) x9
-Glyphs- Ability Power (Greater Glyph of Force) x9
-Quintessences- Ability power x2 (Greater Quint of Potency) Magic Penetration (Greater Quint of Insight)

My masteries are pretty much defense oriented because I need the extra health, armor, and CD percentage they offer. Still, on offense I maxed out only ability power, CD reduction and the 10% Magic penetration. That makes it a 9/16/1 (Do the math if you're interested in my level)

Summoner Spells:

Choices vary as always. I trust you not to pick Promote or Clarity. Surge is not a good choice either. Ghost gives you a good movement speed, but offers nothing more then that. Flash is always a good choice, though you'd think with Shunpo she doesn't need it. I pretty much always take Flash+Ignite, to allow me to possibly tower dive, finish off that pesky opponent that managed to run off with low health, and then safely flash out of there before I get hurt/get hurt more. Flash and Ignite are a good combination, but then again, who am I to judge? This is just a suggestion, you may choose to adopt it, or not.

Starting items and abilities:

We have 3 types of AP Katarinas so far:

1. "I'm French and I'm stupid" - Uses her first point for Killer Instincts, but buys an amplifying tome to increase her attacks (that don't exist until lvl 2 which is just enough to get her killed.)

2. "I'm French but I think twice" - Buys herself a Doran's shield for protection, and spends her point for Bouncing Blade. Great idea, but when matched against 2 heroes, she won't do more then scratch one of them and die after they both rush at her. (Yeah, armor, health regen and hp sound nice, though sadly you can't do a thing but watch your hp melt down if a Jax+Teemo, Master+Trynda, or Pantheon+Jax are your lane opponents)

3. "I'm French and I PWN!" - Introducing the option that pays off - Buys herself the Boots of Speed, and three health potions, to compensate for the health she might lose if matched against 2 heroes at once. Uses her point to get Shunpo, and either jumps in to bring harm, or jumps out and evades death, but returns to battle instantly, after consuming a potion.

We will be discussing the third option, apparently.

We got the potions, and the boots. We have the movement speed and 3x increased time of staying on our lane. That means, more farming, more harrasing, more KILLING! Of course, you will want to make sure that there is not too much running, but even if there is, Shunpo! And boots will do their thing. (In extreme situations, flash+shunpo).

Most people go for a Hextech Revolver, and make it either into a Will Of The Ancients, or the Hextech gunblade. I don't do that. I don't come back to the summoner's platform until I have 860 gold (+35, maybe for a potion). Then, I get myself a Blasting Wand. My runes and masteries allowed me to have 10 AP from the start, so the 40 that the Blasting Wand gives, makes it into a 50, not a joking matter early game. What do you do then? Well, you harass and farm. (if you see that an enemy is running with 60 hp left, you don't focus on killing the minions, right?) A kill and a bit of farming can get you to another 860 gold pretty quickly. You buy a new Blasting Wand. You will already have 90 AP, while your enemies, AP or AD will be struggling with numbers such as 80, 70, or if you're lucky, 60!

What then? You don't expect this build to be made of Blasting Wands only, do you? I hope not, because that would be a waste of time. Make sure you have 3 health potions on you at all times. You never know when it might come in handy. One for when you lost heath in a team fight that you won, but want to push the lane. One if you get ignited, and one if you are slowed in a fight but still running away.

The kills provided by your Blasting Wands should get you to a 1600 gold at some point. Once you have that sort of money, go on, buy a Needlessly Large Rod. Your old 90 AP just got a +80 AP boost, creating a 170 AP in total, making you a versatile match against your opponents who are set back with gold and xp. At this point you are pretty strong and you can very easily fend off enemies off their lanes. Be careful about using your ulti, though, because, if any CC gets you while you spin your death lotus (CC - Slows, Stuns, Snares, Fears) your ulti will be cancelled and you will either be dead or dying. Also, just because you have 170 AP and a channel based ulti, it doesn't mean you can just Shunpo into a 5 vs 1 and expect a pentakill. Be patient. Harass from afar, close in when you know your enemy has nowhere to run, and is lower at least 2/3 health then you. This assassin based style of play will pretty quickly get you to the 1140 gold. Get yourself a full Rabadon Deathcap. Congrats! You've reached 235 AP in lightning speed, leaving your opponents on numbers like 100, 117, 130 at most! You now have a large advantage over them! Still, that doesn't mean you're done buying stuff. At this point, teamfights are starting, which is a great opportunity to score double, triple or quadra kills if the enemy is really that weak. This will lead to a 860 gold faster then ever, adding a Blasting Wand and 40 more AP to your possesion. Why do I keep telling you to get Blasting Wands all the time? Why don't I tell you 'Get a pickaxe, and a vampiric scepter and build that gunblade already? Because my friends, Blasting Wand is a unique cheap *** item that gives you 40 AP and a wide variety of choices. What do I mean by this? Okay. You feel like you're in dire need of a LOT of AP? Get a Blasting Wand and make it into a Rabadon's Deathcap. Does the enemy keep focusing you with their CC abilities? Get a Blasting Wand, make it into a Moonspell Blade, and get Tenacity, which will reduce the time of you being pinned down and helpless. Your opponents are building magic resist armor in order to make your Death Lotus less deadly? Get a Blasting Wand, make it into a Void Staff and watch their helt melt down regardless of their armors. Are you feeling squishy even at lvl 18? No problem, get a Blasting Wand, make it into a Rylai's Crystal Scepter, and get even more AP followed with a large health bonus and a chance to slow your opponnents in a fight. So, yes, all in all, Blasting Wand is a very useful item, compared to the Amplifying Tome, at least from my viewpoint. By now, you should have a Rabadon's Deathcaps and 2 Blasting Wands to make into whatever you need at the moment. While you're waiting to discover whether you'd prosper more from Abyssal Scepter, Void Staff or a Moonspell Blade, get an Amplifying Tome. "Are we making a hextech revolver? Finally! There is no good Katarina build without the Hextech Revolver."

No. We're not making the Hextech Revolver. We're making a Mejai's Soulstealer. We are confident of being able to score kills and assists, and as you all know, Mejai's Soulstealer offers you a AP boost per kill, up to 20 stacks. By now you will already have either a Void Staff or an Abyssal Scepter, depends on your playstyle and the situation you are in.
That leaves you with one Blasting Wand that you can make into a Rylai's Crystal Scepter, or maybe gather some gold and make a second Rabadon's Deathcap. All in all, your total AP should be around 864, which combined with a Death Lotus is bound to bring you a quadra kill in an open fight, considered that you don't get CC - ed. Do you know what this means? This means that with this number, your Shunpo drains your enemy for 875 hp straight off! If followed by a Bouncing Blade, it robs the enemy off another 454 hp. Your 2 abilities with a ridiculous cooldown count will already make the enemy half dead! Is it necesarry to mention what the Death Lotus does? In case you're interested, your channel ulti that lasts for 3 seconds will dish out a total of 365 - 619 Magic Damage to 3 nearby champions, slowing them, and rendering them unable to evade your Shunpo, that will, by the way, be free to use after each kill. OP? Well, no. She has a lot of flaws, but thanks to this build, I learned to overcome them.
For boots, upgrade them at any time you feel like you could use a trait they offer. You can get ANYTHING, really. From Boots of Swiftness to Ionian Boots of Lucidity. The truth is, it doesn't matter which boots you're packing when you have 864 AP. If you want EVEN lower cooldowns, take the Ionian Boots of Lucidity. If you want more magic penetration, go for the Sorcerer's Shoes. If you want higher mobility, go for either Boots of Swiftness or the Boots of Mobility.

I hope this build helped someone, because I know it helped and it still helps me. Now, I'm not saying I'm a pro Katarina player, I'm actually nowhere near that, I just found a way to make her deadlier, and chose to share it with you. Remember, it's up to you whether you will adopt this or not. Any comments, feedback, suggestions, critics, praises and so on are welcome.