Build Guide by CowboyBebop

Not Updated For Current Season

This guide has not yet been updated for the current season. Please keep this in mind while reading. You can see the most recently updated guides on the browse guides page.

League of Legends Build Guide Author CowboyBebop

Bebops guide to ultimate Karthus ownage!

CowboyBebop Last updated on January 9, 2011
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Ability Sequence

Ability Key Q
Ability Key W
Ability Key E
Ability Key R

Not Updated For Current Season

The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.


Brute Force
Improved Rally

Offense: 21

Strength of Spirit
Veteran's Scars

Defense: 0

Expanded Mind
Blink of an Eye
Mystical Vision
Presence of the Master

Utility: 9

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Hi everyone, this is my first guide ever written, so accept the fact it might not be fantastic even though im giving my best to make it a good guide.

Why am i giving you guys another karthus guide?
Well first of all i found that there is a lot of experimenting in the existing Karthus guides, with no one yet to post what i found the most simple yet most efficient way to play Karthus.

I never found any other hero giving that damage output as you can reach it with Karthus,
besides Karthus is either flamed as the 1 button hero or the uber lamer.
Well i take out the 1 button hero argument just because i show you how to take teams apart without even using your ultimate!

This guide is concentrating on the absolute AP ownage and the biggest damage output, while finding somewhat of a really acceptable survivability.

If you start with "FFS lame build, hes using 3 times the same item!" Just leave now and please dont rate OR read my guide to the very end and rate it as an overall guide since you might find it helpful regarding other aspects than only the build, huh? Cheers ;)

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Pros / Cons


  • Possibly the highest magic damage output in League of Legends
  • 1089 AP IS insane!
  • The longer the game lasts, the more you become unbeatable 1on1
  • No one ever will farm better than you do!
  • Who doesn't like to kill others while your officially already dead?

  • Squishy in the beginning
  • Quite often you will find yourself being target nr.1 in teamfights
  • Karthus Mirror Matches are maybe the worst experience you will ever have while playing LoL

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Ok so why did i pick those runes...

We want to achieve heaps of AP in this build so the 3Greater quintessance of insight are self explanatory, the best AP you can get via runes (23.22 AP on lvl 18).

9Greater marks of insight will boost your Mpen a little bit since we only getSorcerer's Shoes. I for myself think this is a better choice than getting 1.8 AP each.

9Greater seals of knowledge will assist you with your Mana pool because our plan is to turn heaps of our mana in AP.

9Greater Glyphs of Force will, again, boost your AP, well i think those are self explanatory...

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I chose the 21/0/9 way because the 5% extra damage greatly pump ourultimate and ourLay Waste. As you ask yourself now "wait, lay waste +5% that guy is nuts", 5% of a 400 damage lay waste really does stack up, when you think about spamming one every second. Also, the 15% Mpen are a must for every caster.
Most of the other points spent in the offense tree are used to make your lasthitting a little bit easier early game, giving you armor penetration, more base damage and attackspeed.

The 9 points in the utility tree focus on our regeneration and on our mana pool, again, as mana means AP, we want to have heaps of mana.

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Summoner Spells

As Summoner Spells i choseTeleport andFlash.

Teleport allows you to greatly increase mobility. Use it early game to insta heal in your base and be back on your lane in 5 seconds. While regenerating you can easily go shopping ;)
During mid game you can use it to teleport all around the map, defending towers (As you kill creepwaves within seconds due to Defile) or just catching that 30 creeps trolling around somewhere on the map. You will be first most times, stacking huge amounts of exp and gold!
Also its always nice if you dont have to run over half the map if you decide you go for a gank.
Teleport to that creep out of enemy sight and run the last 10m through the forest, nearly giving them no time to call any misses.

Flash on the other hand is your All-In-One Spell for everything. Use it to chase heros, use it to initiate that gank (More in gameplay), use it to escape through walls.
Its best purpose early game might be to save you in mid from death. Sometimes it happens there is no miss called and that Jax and Sion come out of the bushes, attemting to gank you.
Yes, you might cast your Wall of Pain, but hey, stun is stun and you will be dead...
Cast your wall towards them, start running for your life and teleport towards your tower will save your *** in 99%.

You wouldn't need clarity as some people take it because i reckon we will achieve the biggest mana pool this game has ever seen and Defile gives you more mana regeneration than anything else.
We dont need exhaust because we have our Wall of Pain to slow the enemy and hell no, we dont need Ignite since we have quiet enough damage output already.

Some people like the heal or other stuff but in my opinion those 2 are the most useful Summoner Spells for Karthus.

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Skill Sequence

I always keep the focus on Lay Waste as you will use this spell to lasthit creeps and to harass enemy heros. In 1on1 Situations the double damage turns nearly all fights to wins, with you probably seeing that Ashe losing 1/3 or half hp thanks to your little bomb.

Skill Defile on level 2 to enhance your mana regeneration as soon as possible and DO NOT
forget to skill Wall of Pain on level 4. You wont be skilling this for a long time afterwards,
but in fact, you need the one lvl of slow just to make it easier for you to catch up with Defile when chasing enemies.
If you forget Wall of Pain on lvl 4, you have to sacrifice one level of Lay Waste to get the slow before turning 6.

For the rest, always max Lay Waste and Requiem when possible, followed by Defile and finally Wall of Pain.

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Start of withMeki Pendant and 2health potions. As soon as you can get theTear of the Goddess cause we want to start stacking up mana as soon as possible.
Continue withBoots of Speed.

As the tears' effect is Unique and the same as the one inArchangel's Staff, we now can focus on our next item.
Start off with anotherSapphire Crystal and try to be quick buying the rest ofCatalyst the Protector and finallyRod of Ages.

Until here everything should be done as quick as possible for several reasons:

  • Tear of the Goddess should start stacking mana as soon as possible
  • You want your Rod of Ages bonuses as soon as possible and it takes 20 minutes to get them all

From here on everything is way more relaxing. Finish yourSorcerer's Shoes and after that your firstArchangel's Staff.

Now you got some time to focus on yourRabadon's Deathcap. I usually start withNeedlessly Large Rod but in fact it doesn't really matter.
Once you got it, always get yourBlasting Wand first and then finish it and get the rest of your other Archangel's Staffs.

YES This is heaps of money but hey you will be the farming god and the hero killer Nr. 1 in the game.

I always tried out other items aswell, but what i found is:
  • We dont need Rylai's Crystal Scepter as we have enough slow with our Wall of Pain and Hp from Rod of Ages
  • Instead of getting Magic Penetration Items i like to go for the pure Damage as at some point it is just overwhelming. Of course if the whole enemy team goes Magic Resistance dont hesitate to get Void Staff or Abyssal Scepter
  • Some of you will cry for Mejai's Soulstealer. I don't get that item because Karthus is a hero which i play more aggressive than any other. Just give them hell a lot damage and if you get killed, finish them off with your ultimate (due to your passive). You will be dead but your team will be thankful for being alive fighting 1 or 2 opponents with hp low as hell.
    Mejai's is made for heros which are STAYING ALIVE but since we don't mind Dying we won't buy it!
  • Zhonya's Hourglass... Well i thought about it and tried it out. I think those 2 seconds dont help you in any way. If you are going in a teambattle and want them to get damage from defile so you activate hourglass, they will simply run out your area of effect. If you use it as a last second saver when you are the main target of the enemy team, most time they just slay you two seconds later. Plus we got our flash which is our main escape tool.

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Early Game

Start off withMeki Pendant and twohealth potions and go on the mid lane.
UseLay Waste to lasthit creeps and to harass the enemy hero. Remember that single targets get double damage, so always try to hit the hero and only the hero.

For me writing my first guide it is hard to give you tips on how to control your hero as i have only words written to describe what i mean :D

I can tell you one thing, most of the new players just aim their mouse on the enemy hero and press Q. It does take a while to get the hang of it, but the secret for all players who play Karthus for the first time is: Don't aim your bomb where the enemy is, aim it to where he is walking!
So if the enemy would run in a straight line, put the bomb in front of his feet so it explodes just when he walks on it. As the skill of both you and your enemy raise, it will be more and more of a cat and mouse game, but as you carry on playing Karthus you will find it easier and easier guessing where the enemy is going.

If everything goes well, you will either a) kill your enemy, b) force him to play super defensive or c) make him go back to base quite often.

It is really important that you go back to base as soon as you have 605 Gold, or in case you got the first blood or a kill 955 Gold. Rush for yourTear of the Goddess as it gives you (together with Defiles' Passive) unlimited mana even in the early game.
Use your teleport to be back on your lane immediatly so you don't lose that much experience.

Your main priorities are harassing (killing) the enemy hero and trying to get every single creep kill on your lane to rush for your tear.

Mid Game

Once you get your ultimate start using it whenever you get a chance. If you play single player games, let your team know "Got ulti" so they can call it if the enemy is escaping somewhere else. Always watch the minimap to see where enemies are close to one of your towers. Even if you are not there someone else of your team might go for a gank.

Here is now what we call the big difference between Karthus and Karthus players.
The bad Karthus player just waits with ulti until his mates bashed the hero to 500hp and starts casting his ulti so by the time it is casted the enemy is down to 100 to 200 hp.
I call that not teamplay-productive worst killstealer behaviour ever found in multiplayer games.

You want to be the Karthus who either
a) sends in his ulti as soon as your mates engage to make it easier for them to get the kill
b) keeps his ulti to the very end and uses it to kill that 50 hp Ashe running away with haste

Both acceptable ways to stack money (in a) assists, in b) kills) and your team will be more than thankful. Again, LoL is a teamgame and how often did i see the noobs winning over 1 or 2 pros just because they had amazing teamplay and were ganking as hell. If you are hated by your team (it's easy to be hated as Karthus), its way harder to win.

As you are level 8 or 10 and your Defile starts actually doing damage, start ganking.
Go back into the fog of war so the enemy doesnt see what you are doing.
Use your teleport to one of the sidelanes, but make sure you are still in fog of war when arriving.
Go the last piece through the forest, still unseen.
Blink through the forest to the enemies, activate Defile and cast your Wall of Pain towards their tower (or if they run somewhere else, in that direction).
By that time your teammates should have joined you and you just bomb the **** out of them using your Lay Waste.

I think you win most of the fights for 2 reasons:
1. there is a really short amount of time that you are missing on your lane so it is possible they are not prepared well (there is no "miss" called).
2. Surprise effect is on your side: There is nothing worse than a 2 level higher Karthus popping out of nowhere, blocking your escape path with his wall and dealing heaps of damage.
Suprise nearly always ends up in Confusion and Chaos, at least the first couple of times.

After you finished your Tear of the Goddess just grab some normal boots and go straight for yourCatalyst the Protector. Try to be really quick and finish it to yourRod of Ages.
It will be the only item giving you HP bonus so its nice to have early, PLUS it takes 20 minutes to reach its full potential.

Late Game

As the game continues just continue getting the rest of your build in the order described earlier. You running around ganking people and getting kills with your ulti should have given you plenty of gold during midgame.
Now you know those moments when the first towers are down and there are HORDES of creeps fighting, half the team running there to grab some money? Simply teleport there and activate Defile. 3 Seconds and you killed all of them, giving you heaps of gold. You will finish games with 350 creeps killed more and more often.

As the game goes on and teamfights come up, wait for you tank to engage and the run/flash in the crowd with defile. As i mentioned earlier it DOES NOT if you die (okay, your Rod of Ages gives you quite some HP). You will do so much damage even 8 seconds after you are dead its enough to kill their entire team.
Remember that in the lategame your Defile does more damage compared to your Lay Waste. Yes for single enemies Lay Waste is awesome but for teamfights you want that insane damage output Defile gives you.

Therefore you want to be IN the battle, not standing in the back throwing in some bombs!

Well if you play like that it shouldnt be any hard to win your games. YES you don't have 20/0/0 Scores, they might look like 14/8/6 but hey your team wins and that is what counts!

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Unique Skills Or The Math Afterwards

So some of you think "hey that is impossible" or "how can defile be that devastating in teamfights?", well here we go:

2370 HP is in my opinion way enough for a caster

With more than 4482 / 5482 (the 2. one is plus the 1000 possible mana from Archangel's Staff) Mana,
each Staff gives you 134,47 / 164,46 AP
adding up to a total of 842.18 / 914,14 AP

Now we got Rabadon's Deathcap, giving us a nice 30% Boost, which makes it a total of
1089.43 / 1188,38 AP

Ever seen that much AP? i havent!

Ok what does that mean to us?

Lay Waste does a Maximum of 476,51 damage, plus double damage for single targets

Defile does 407,09 damage EVERY TICK and you can basically have it on the whole time

Your ultimate does 1381,86 damage to all heros. Use it to initiate fights and bring them to half hp immediatly!

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Thanks for reading the guide guys, i just couldn't find anything better for Karthus then that and i play him close to every day!

As i mentioned this was my first guide and i didn't know how i could use those mini icons where the description of the item/spell pops up if you mouse over it.
I'd like to change those cause for now i can only use those big images without any mouseover-description ;)

Rate fair, Have fun playing and see you next time,

Cowboy Bebop