This is my first build, let me know if you have any comments by leaving them here, or email me at james_lamb3@yahoo.com with KARTHUS FEEDBACK in the subject line.

Item icons and pictures coming soon........

I'm fairly new to the community and only have a level 25 account, however I have found that many of the people that I run into while playing 5v5's can't manage their Karthus character very well. I kept looking for a build with a high rating but it never came, so I've adapted mine from 3 that I really like. The three are each fairly good, but are a little off and haven't been updated for the new masteries. That being said, I've gone head to head with other Karthuses in mid lane, and have never lost mid to them. This is probably the best build I know of for someone looking to go full AP with Karthus. Without further ado, lets get right into this setup. Even if your team doesn't walk out with the win (most of the time its because they expect you to initiate) you still walk away with tons of kills, as you can see here:

So the runes, as you can see are geared only to increase your AP. Which is really what you need, since you have enough survivability with the health pots and heal to live through the squishy part of your laning phase and your mana pot and some discretion on casting lay waste will refund some of the mana you lose while creep farming. Karthus is a character who's gameplay and communication revolve solely around his ult.

The masteries are built much like the runes. All of the runes are built to increase AP and damage especially when they are their last leg. That's why executioner is fairly important to this build. You can see this build adds 22 AP and increases the amount by 5%, and when you're talking about over 1000 AP at full build 5% ends up being alot, and it stacks with Rabadon's DC.

Since we've established that we are boosting your AP, we are trying to stack as much AP into your items with minimum attention to survivability. You always wanna start out with boots ,2 health pots, and 1 mana pot. This gives you mobility to harass using Q (lay waste) while being able to avoid the return damage they will no doubt try and lay on you. It also allows you to survive early game ganks, sometimes I've had the entire other team try and kill me right out of the gate, and it never works as long as I have the pots. Sometimes if I quickly overpower the enemy champ in mid lane, I will recall and grab an extra mana pot. One of the downsides of this build is that if you spam Q and E you will lose mana really quickly during the laning phase. Generally speaking, you should try not to recall until you hit level 6 and have 750 to upgrade your boots. After that, your Tear of the Goddess should build fairly quickly and the Archangel's Staff will follow suit, If you notice that you don't have the Sorcerer's boots, Archangel's Staff, and a spare blasting wand by level 10 you should start laying the E (defile) on thick. Using it together with Q is really important. After that you just pick up kills and farm mins to get the remaining weapons. You should hit full build around 60-70 minutes into the game, and by then your ult will hit for 1200+ and all enemy champs will be forced to waste item slots on Magic Resist items.

If you find that you are getting steam-rolled by one character class or another, don't be afraid to pick up a magic resist item or armor item to make yourself less vulnerable until you get a couple rabadon's deathcaps in your inventory.

Unlike some other characters, Karthus' skill sequence isn't the same for both dominion and classic modes. In classic mode you're going to want to build up your main harass skill, Lay Waste (Q) fairly early. It is helpful to build a fairly strong defile or at least have one early game to deter melee champions away from attacking you, and to add extra damage on top of the damage you already do with lay waste. It is also helpful to instruct your teammates to fight close to where you die, so that the skills you can cast up to 8 seconds after you die help turn the fight around to their favor. Late game it is important to trap them with your wall, and then chase them with E active while spamming Q. Hitting them after they've run through your wall is a good way to add more damage to your already lethal attacks due to their decreased magic resistance.

In dominion however, due to increased movement speed of everything, I have found Defile and Wall of Pain to be more usefull. I normally level Lay Waste once, and then max it out last, partially because I've found it so hard to land on moving champs. The item sequence is the same though.

For Karthus I primarily use ghost and heal. I've had some people ask me why I don't use abilities like surge or ignite. Surge seems like a great idea for someone that's full AP. However the truth is that it just doesn't add that much too be viable over the ability to keep champs in your defile via ghost or the ability to survive early ganks AND late team fights. The problem with exhaust is that while it does the same thing (increases your speed relative to your victims) it only targets one champ, if you ghost you can keep up with multiple champs instead of picking one out of the bunch.

Pros:

He is great at clean ups from team fights, those champs that always get away don't anymore.

He gives really great map coverage, you don't have to be in a team fight to earn kills and assists in it.

After he hits level 8 or 9 he jungles like a pro.

Cons:

There are characters who can jump over or move through your wall, like fizz. Or ones that can dodge your ult by healing or using skills, like Gangplank eating oranges. Try and wait till they've blown their summoner skills and used their champ skills before firing the ult.

Karthus is really item dependent, you can't count on being fed, you have to be aggressive and devour.

When Karthus' wall is on cooldown he is susceptible to being ganked. And his wall has a longer CD.

His ult also has a 2 minute CD, you can't afford to just use it on a whim, and they know its coming.

Karthus was made to hog the mid lane. In the early game your going to want to auto-attack minions and then finish them with your lay waste, you have to use it with discretion because he will become starved for mana quickly if you just spam it. You also want to keep him moving when you're popping in and out for Q spam on enemy champs. When you lane against melee champs play conservatively but chances are if you act weak while your heal is up, they will try to turret dive you, then you simply wall trap them, pop E, and spam Q. Nothing works better. When laning against other casters like Veigar and brand, remember that mobility will solve most of your problems. Keep moving to avoid getting hit with their nukes. Also remember to stay behind your minions. Ranged champs that are a little bit of a pain but easily manageable with some skill include: Veigar, Brand, Morgana, Heimerdinger, Ashe, Vayne, Caitlyn, Lux, and Xerath. The ranged or mage types that you NEVER want to lane with are Leblanc and Anivia. Swain is substantially harder to lane with than those on the previous list, however not nearly as bad as the two I just mentioned. Leblanc is super hard to hit with her flash damage and constant teleportation, while Anivia does way more damage than you early game and you can't kill her egg in the first half of the game. Other ranged or mage champs are really easily disarmed. Teemo, graves, keenen, kog'maw, orianna, annie, and vladmir never offer much of a threat when you just move and stay behind minions except to finish a kill.

When mirror laning (laning against a Karthus) just remember the tricks you'd use. Watch out for his wall, keep moving, and try and build a stronger defile than he does. Its also more important to recall more often after he hits lvl 6 and try and kill minions to buy items more quickly, chances are, if you use this build you can outplay him.

After you hit level 8 or 9 you should try and jungle the blue buff. It will decrease the frequency between your recalls, keeping you in the lane longer and increasing your damage output.

Killing enemy champs and effectively assisting your teammates will rely on their communication with you. Ideally, you should keep them posted on your ult's damage output, and how long till it's ready to fire. However, this rarely works. I normally have to monitor the map while i'm a moving to and from lanes. Occasionally you will get a good team but don't count on it. You should also never expect to initiate with Karthus. Ulting can happen in two places, either 3 or 4 seconds after your teammate has initiated, or after everyone is starting run away. Ideally you cast it when 2 or 3 champs are at 1/4 - 1/3 health. It really comes down to whether you want kills or assists.