Hi Mobafire people!
I've been playing Karthus for some time now, and I feel that I wanted to make a build for him. Many find Karthus to be a noob champion, because of his ulti, but I find him funny to play - He is a great farmer and good at harrasing. Since the last patch, where Zhonya's Ring was changed, he has become even funnier to play in my opinion. I don't know if a guide is needed, but I felt like making one. I hope you'll enjoy the build.

This guide is updated for patch 1.0.0.118b from May 2011

Change: Added Void Staff to the core build and changed the item sequence to get Archangel's Staff later.

Death defied - passive This passive allowes you to cast spells for 8 seconds after your death
Best used to cast your ultimate and help your team win a teamfight. If you have the mana just toggle defile on and the enemy will drop health fast!




Creates a delayed blast at Karthus' cursor position. After 0.5 seconds, deals 40 / 60 / 80 / 100 / 120 (+30% of ability power) magic damage to each nearby enemy, this deals double damage if it hits only a single unit.

Cooldown 1 seconds | Cost 20 / 28 / 36 / 44 / 52 mana | Range 875

- For Karthus, this is what bewbs are to dudes - Sweet Beans! This is your main farming capability, until you have enough mana to keep up Defile, when your taking down another wave of minions. You will want to max this first, as it is your best harrasing skill and it gives you many minion kills. And minion kills restores a bit of your mana. It will benefit you most to use it on the ranged minions, as they are easier to kill. In early game mostly use it to farm, as it is quite easy to avoid, if you aren't pro at using it (I'm not that good myself).
- When you are dead, try to take as much HP as possible with this. It can grant you assists or even some kills during a game.




Wall of pain Creates a 800 / 900 / 1000 / 1100 / 1200 distance wide wall through target point. Reduces enemy armor and magic resistance by 15 / 20 / 25 / 30 / 35 and reduces movement speed by up to 40 / 50 / 60 / 70 / 80%; debuff lasts 5 seconds. The wall lasts 7 seconds.
cooldown: 22 seconds
One of the best gank tools / debuffs in the game. Set a gank or escape from enemys. This ability makes the difference in teamfights!




Defile Toggle Off: When Karthus kills a unit, he restores 20 / 27 / 34 / 41 / 48 mana.

Toggle On: Drains 30 / 42 / 54 / 66 / 78 Mana to deal 30 / 50 / 70 / 90 / 110 (+25% of ability power) damage to nearby enemies each second.
cooldown: 0.5 seconds after toggeling off
Very strong AoE spell. Your late game farming tool as well.




After channeling for 3 seconds, Karthus deals 250 / 400 / 550 (+60% of ability power) magic damage to all enemy champions (regardless of distance).

Cooldown 180 / 150 / 120 seconds | Cost 200 / 300 / 400 mana | Range 10000

Cooldown 0.5 seconds | Range 550

- If Lay Waste was bewbz to boys, this must be what Robin is to Batman. (I don't know if that's better than bewbz, but I did not know what else to say.)
This spell will grant you a lot of kills if you use it well. It is mainly made to finish of enemies with low hp. Make sure that your teammates tell you, when to finish someone off. And they better tell it fast, because it pisses Karthus of, when his ulti is wasted and he can't finish the next enemy off. It really sucks if they have Banshee's ready or Zhonya's active. Then they will ignore the spell, so try to see if their Banshee-shield is up, before you finish them off. When you have used this spell, try and get the blue buff for cooldown reduction. Just make sure that you get some kills with this, because you need to get fed, to get items. If you are under-fed, you'll have a hard time, believe me.

TELEPORT[/h1

]
: Karthus will get mid very often and in order to stay on the right amount of mana, or you have to come back for items, teleport will be very usefull. Another way in which teleport stands out is tactical map usage. Sounds strange? Let me explain it to you. Often you and your team push a lane and find yourselves blocked by the enemy. Everyone is just standing there doing nothing. With teleport you can swap lane fast and go for a turret kill or force the enemy to split. With the ability to devastate turrets (explained in the item section) and superb push capabilities this is an excellent spell for Karthus.

FLASH

(advanced players): Karthus, just the same as anivia, has low survivability, and is pretty slow. Getting away will always be a problem. CC (crowd control) has the upper hand when it comes to getting away and be killed by the enemy. Then your wall of pain will be of no use. Flash is the solution. Getting away from target range and have all the time laying a nice wall of pain! This skill should only be added if you won't have to get back all the time for mana.

(9-0-21)


Offense
I take 9 in offense, mainly to get that extra spell penetration from Archaic Knowledge. It also gives you some extra ability power and cooldown reduction.

Utility
I go with 21 in utility to get:
- Mana regeneration & mana
- Extra xp
- Lower cooldowns on my summoner spells
- Lower cooldowns on my abilities.

You can go with other mastery trees, if you prefer. This is simply my way, which fits me the best. I think mastery trees are quite individual - You could go defensive for better survivability.