Pros
Great Farming
One of the highest Magic DPS potentials in the game
Rage inducing Ult
One of the best slows in the game at 80% AND MR+Armor reduction. Pure awesome
Isn't afraid of Death and will likely take someone with him from the grave

Cons
Squishy
Especially weak to burst Unless you build for it
Takes a lot of time to master

Runes are simple.
Magic penetration reds as they are the most valuable to have.
AP/level seals and glyphs because by the time you hit level 6, they give the exact same amount of AP as the flat ap glyphs/seals.

AP quints because the per level ap quints are simply not as good at level 6, they only give 2.58 AP each then, whereas your flat AP quints give 4.95 each.

This setup is best because you really want your first Requiem to kill its target, nothing is more disappointing than messing that up, and the lost gold can have a real negative impact as the cooldown is quite long at level 1. These runes alone will give you approx 29 AP @ level 6 for "free."

Rushing negates any need for extra mana regen. Cooldown reduction runes are not worth it on karthus as it only benefits two spells and IMO they are on balanced cool downs not worth investing in more than masteries + blue pots.


Masteries:

Standard. Never go without free 15% magic reduction (early game this is near nothing, late it can be free minus 10 to 15 which is really good for a mastery)

Utility is just super good on casters, the 9% CDR for free is all you'll really need. You also benefit from the mana regen and movespeed, as well as buff timer if you end up with blue. Greed is taken because I'm greedy. ;)

is your best spell to level first. Learning to hit with it is crucial to mastering . It can be very useful for last hitting, provided you always try to only hit one minion at a time. The lay waste explosion effect range can be seen if you hover your cursor over the skill. If you've never played Karthus before, take him into a custom game and practice a lot in hitting specific stationary minions for a while. Then only try hitting certain ones when they're moving. Once you get a good feel for the delay and the area you'll be pro at it.

is taken at level 2 for its passive mana regeneration.
It is leveled up last because it is a late game spell. Using defile in lane for harass is bad play. There is no faster way to go out of mana and become useless. Early game you only use defile when going for a kill. After level 9, if you wish to alternate between Defile and Wall that is a decent idea.

Level 4 is when you get this, and when you have wall you can seriously injure your opponent. The trick with when 1v1, is to simply drop it right on top of your enemy!

In this way the slow is unavoidable and immediate. If you get your opponent injured, drop a wall on him and really make him feel the "pain" of lay waste spam.

Now if someone charges you instead, then back off dropping lay waste along the way. You really need to evaluate your opponent as Karthus, so that you can accurately predict their movement pattern.

If you are not doing well with harass then you should wait until level 6 to attempt using your wall. Then if you Q them enough, you'll put them into Requiem kill range.

Do not underestimate leveling up wall of pain first, as it is not just a powerful slow, but also a good MR/armor debuff to all who pass through it. It is more helpful to your team than extra E damage at this point in the game.

Landing Lay waste on moving targets can be hard, Landing it on people who've been slowed is not.

and are optimal.

Why teleport? A few reasons:
1. Lane presence. Quickly farm up 995 gold, then B and buy your Tear + Boots. Tele back
2. Getting to team fights, surprise ganks, tower saving and tower pushing. Karthus kills creeps insanely fast, and late game he can kill un-attended towers as well because of his high AP.

:
Other than your wall you have no way to escape, and a level 1 wall probably won't even save you if you're caught off guard by a jungle gank.


Acceptable

If you want double escape summoners then take ghost but be warned that in most cases this will not help you.

If you get the mastery point, Exhaust+Wall can be brutal combo in lane. It can actually be a really good spell on him, I just love teleport but there is no denying that exhaust is a fantastic karthus spell.


Also if you want to be cool like PhantomLancer and Dyrus then you can run Revive. This can be an incredibly powerful technique when the right situation arises but you better have good judgement on using it.

Clarity is un-needed once you get tear of the goddess and becomes incredibly useless late game.

Early Game CORE ITEMS (as in, do not skip)


Note: Take Boots + 3 pots to start when facing a skill shot champion such as Brand, Orianna, Ezreal, Urgot, etc. Consider taking Boots + 2hp pots + 1 mana pot to afford some harrassing. Boots 3 pots is probably ideal unless you are completely unafraid of the enemy.


-- Simply put, you need mana. Nobody can get the passive faster than Karthus can, it's made for him.

-- The boots of choice, you need penetration and none of the other boots really help Karthus much at all.

-- Sustain, and against non burst champs it will make you godlike in 1v1 battles.

Mid Game Items

-- Pure and simple every AP carry needs it.

To start building your Banshee Veil

- Helps kill everyone. Either people are buying MR or they're about to by the time you get this, so it's only logical.




Late Game
-- You should be on the upper end of the mana stacks. HUGE boost to your AP

- Choice defensive item as its the only MR you'll have and it comes with health + a spell shield.

Blue Elixirs. Nice extra ap.

- If enemy doesn't really build MR you can get a **** ton of reduction with this item + Boots + Your Wall of pain. Upwards of -80 MR, making void staff unnecessary.

Very expensive item but one that can be very useful on Karthus in some situations. If you're very PRO at using the activation it can be more helpful than banshee veil.

Fairly expensive item but you can torment an individual with Lay waste shots, and your defile will slow----but only on the first tick of damage. This is more suited to a bulky karthus build, which is a different way of playing him.

At level 6, your Requiem base damage will be 267. (Only counting runes as your ap)
This chart shows you how much damage you'll deal based on the Magic resist of your target champion. It shows the assumed base MR in the first column, followed by their effective magic resist against your spells and the damage that R will do.

Obviously if you have your sorcerers shoes by level 6 or your first time using ult, it can make a substantial difference in damage dealt.

In your first requiem, you will need to ensure that you get a kill or an assist. This is simple, see an enemy below 200 hp with no way of healing or dodging and they will die unless they have 50 MR or higher. Alternatively you can coordinate with your lanes and jungle if an enemy is very overextended, and greatly increase the jungle gank success rate. This second method requires a lot of trust in your jungler, be wary about that in solo queue as you have to wait a long time to use it again, and Karthus needs the gold.

Late game, you need to be watching your enemy. Do they all have banshee veil? If so, then you can rule out using as an initiation. In fact, in Solo Queue I strongly strongly suggest that you do NOT use it as initiation. If your team doesn't immediately capitalize, then you just wasted your ultimate.In an arranged team this could be very useful and give you a good advantage knocking off 500-800 hp of every enemy.


Mostly you want to Q from out of their range and lay down a Wall of Pain that hits as many as possible. Wall of Pain debuffs MR & Armor so it helps everyone on your team deal more damage.

Now once they've taken some hurt, you can enter the battle. You can't be afraid to die as Karthus, and you also have to know when it is okay to die. If your team is ahead or it is a very tight battle go for it. If not you'll have to try and pick people off with lay waste. If they just obliterate your team mates, well then gg you won't be able to do much.

Karthus thrives on being with AoE stuns. Any champion capable of snaring/stunning the enemy team will make your life easy. Let them initiate, then place wall and flash in with Defile on and Qs flying everywhere. It won't matter if they kill you because your team will assuredly win the fight.

If you get Zhonya's, you can take focus, Hit your active with Defile on, and then die.

When purposefully letting the team focus you it should be obvious to ult after you are dead to avoid interruption.

In fact, never ult when you are alive unless you are miles from the fight. You will get interrupted or simply killed. Always have defile on while dead. If your team can keep them in your circle of death, then it will be easy win. To be safe, don't cast more than 2 lay waste bombs before ulting or you'll run out of time after that damn nerf. Try to have wall ready when you're dead.

Karthus LOVES LOVES LOVES having on his team.

Jarvan IV is great to have both as a team-mate and an enemy because of his ult.

Galio is just as great as amumu if he can get his ult off and nobody interrupts it.

Soraka, because troloolololol global damage and global heal.

Sona for AoE stun ultimate

Fiddlesticks as your jungler is pretty amazing. Land one good wall while Fiddle channels Crowstorm and ace the enemy. (factor in that Defile and Crowstorm combined is an INSANE amount of DPS people are taking, and with the slow from your wall their only hope is flash, but you can just flash after them. Anddd fiddle passive + wall debuff is like -40 MR)

Every physical AD except for Caitlyn and Corki should be incredibly easy to lane against. They all move pretty predictably and have to stand still to hit you. will melt them. I say Cait and Corki are harder because of their very good pokes. Also cait range and ult will own you if you miss even one chance to Q her, so she demands perfect play.

AP opponents are a much different story.

She will own you if you're not careful. Her walking pattern however, is painfully obvious when she has a stun. Just kite her and she'll back off. Never chase her if she still has that stun though or she'll melt you. If she carries flash and ignite, you need to know that at level 6 she can one combo you if you're at 30MR. Save your own flash for when she tries this. As soon as you hear her flash, you flash away.

Well this will just suck. His Q will destroy your health and it will silence you too. His only weakness is being melee so you can keep him away from creeps with lay waste. You should switch lanes in all honesty as you're just begging to get destroyed. His dodges but it has to be timed perfectly. **Note, if you will lane against Kassadin, you NEED to buy your Negatron cloak immediately after your Tear. NO EXCEPTIONS, it will greatly reduce the damage his Q's do to you and allow to farm without dying.

She is heavy, heavy burst. If you take her combo you are dead. She is squishy though, and you need to scare her with how much Lay Waste will hurt. Play extremely cautious, this lane is still winnable. Your farming should easily be better than hers.

If you can dodge her Q you will have no problem. Her Q is one of the slowest particles there is, but it still may be a good idea to take boots first. Don't forget about her egg.

Dodge Nevermore, try and kill pre-6. After that you should only try to kill with none of your own minions around. You should have no trouble farming creeps though as swain is a slow walker, if he comes to harass hit him with some land mines.

His pool dodges never forget it. He normally doesn't buy magic resist early on, and is extremely predictable in movement, you should be able to handle him no problem pre-level 9. After 9 he is more of a chore. The key is to exploit how hilariously weak he is levels 1-5.

don't get stunned or you'll die. You should probably start with boots against him. Focus on out farming him early on until you get some items. Never give him free damage with Conflagration, so whenever he farms your minions with pillar of flame, just back off til the blaze is gone. You can fairly easily just farm the entire laning phase or fight, it's up to you.

You need to dominate him early. He is very squishy like you except you can harass a lot more and a lot faster early. Once he has ulti and some AP back off. In late game he is your mortal enemy. Without your Veil passive up, he can easily one shot you.

BUY BOOTS level 1. Simply put if you dodge his Corrosive Charge, you will most likely be able to win. If you get hit by it, prepare to be raped.

Lay Waste will reveal any champions it hits in bushes and fog of War
Wall of pain grants 7 seconds of sight in fog of war, like a mini Clairvoyance However it no longer reveals champs in the bushes.
Wall of pain will also debuff all jungle creeps including Dragon and Baron
Extreme late game a Defile>Flash>Zhonya Combo is a great initiation.
Karthus kills Baron very very fast and with WoTA you should not be afraid to tank him for your team. In some cases you can solo baron on your own, though it requires you finishing your AA staff sooner than you want too. Death Cap, WoTA, AA staff built soon enough, and you can solo. I'll make a video if i get bored enough.

**Have good map awareness, be wary of team mates calling for to ult. Learn all heals, shields, and ways Req is avoided.

Once you get Revolver, you're much stronger with enemy minions close by in lane. Defile=constant healing

ANYONE foolish enough to stand in one place and 1v1 you is going to lose provided you both are not at a level disadvantage or fighting a burst caster.

Once you have your early game core, Karthus ganks can be very strong with Wall of Pain, Lay Waste and Revolver to keep you alive. If your enemies have over extended or you can help your jungler, then do it!

DON'T risk fighting 1v1 if your enemy stands next to his minions, this

severely lowers your DPS

Q is easy way to pop banshee's veil.

Thank you for viewing my build. I hope it helps you.

Season 2: Record so far: 13-3

Build 2 is the generic build you could make if don't like being squishy. You should take this path if you are a new Karthus player as it will be obviously more bulky, and still deal good damage.

Build Catalyst>Sorcerer's Shoes>RoA>(rest of build)

Take Mana regen runes for Seals since you won't have tear.

8/5/2011 - Made note of what I consider core to build 1.