whats up Mobafire peeps!
Ive been playing LoL since beta and Karthus is one of the champs that I've stuck with since I first played him. Most other Karthus that I see never seem to play the style that I play so I figured hey lets make a guide!

Hes one of my favorite champs because I feel that he is well rounded. Hes a good farmer, he can harass with the best of them , he has possibly the best ult in the game :D and he brings a ton of utility to any team.

This guide is my play style. Not the best way to play Karthus but a fun way. It is centered on nuking down and basically steam rolling under leveled champions If you can pull it off like I do, you will steamroll and carry your team.

Pros:
-Awesome farmer
-Can almost always win mid
-Good control of baron and dragon
-His ult is a team fight changer
-Awesome passive which allows for kill cleanups
-Really hard to gank or runaway from

Cons:
-Definitely needs to be fed to survive mid and late game
-Squishy and easy to kill if not positioned properly or Wall of Pain is on CD
-Item dependent
-Constant QQing

Terms used:

CC = Crowd Control (Stun, fear, slow, snare, etc)
AP = Ability Power
AD = Attack Damage
MPen = Magic Penetration
CDR = Cooldown Reduction
OOM = Out of Mana
HP = Health/Health Points/Hit Points
DoT = Damage Over Time
AoE = Area of Effect
MRR = Magic Resistance Reduction
MRes = Magic Resistance
CS = creep score
MS = move speed

Death Defied

Upon dying, Karthus enters a spirit form allowing him to continue casting spells while dead for 7 seconds.

-This is a awesome passive! The best for cleaning up kills whether its with Requiem or with Lay Waste spamming. Also good to switch on Defile while in the passive as it will damage if you die in the middle of a team fight.

Lay Waste

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

-This skill has to be...contrary to popular belief, his bread and butter. This is your main farming and harassing utility. Its pretty strong early game and takes a bit to master but when you do!!! It does double damage if it hits a single target. This means a couple things... #1 it will do a **** ton of damage if landed correctly #2 You can tear through dragon and baron.

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 | Cost 100 mana | Range 1000

-This ability is underrated and underused by most Karthus. It has a HUGE range and slows whole teams. This combined with Flash makes you a real hard karthus to kill. Great in team fights because you slow, reduce MRes and basically distrupt ****. People fear the wall remember that!

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.


-This is the gold maker and killer late game. Good to take out whole minion waves and gain good mana back on last hit. You will tend to go oom early game if not used correctly. Very good in combination with Zhonya's Hourglass it still works while in stasis.

Requiem

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


-Now...how do I put this...its the big daddy of all ulti's. Be prepared to hear "noob champ" "cheap ult" "L2P" but thats the fun of it. This spell will grant you and your team alot of kills. Karthus on a basic level can clean up one or two kills with this ultimate and on an advance level can get your team an ace if used in fight. Its always good to keep attention to players items and skills when using this skill. If you ult sivir and she has a spell shield then you just wasted your ult. Also pay attention to banshee's veil.

Recommended

Probaly the best summoner spell in the game. Great to set up a kill and survive a gank. In combination with Wall of Pain this makes you really hard to kill and saves your Mejai's Soulstealer stacks.
Another skill that helps your survibility. Helps you chase down enemies and run away from them. Also good for getting to a lane to save a tower

Okay

Good for map control and gets you back to a lane fast. Good way to also get to a team fight and sometimes undetected.
Good way to chip them down and get an ult off. Also can be used to secure a kill in lane
Another good skill to use to escape CC. I see this more useful in ranked games

No way

Sounds good on paper...more mana right?!?! Not really. It is a waste of a spell and you should be able to monitor your mana enough to not need this spell in the first place.
Leave this one to your AD carries

***Rest are left out for obvious reasons***

Here I go with
magic pen marks for more damage.
Flat armor seals for early game survivability
Flat cooldown glyphs for better cooldown on wall and ult
and for quints I go with flat AP so that you can gain some early dominance

I start with Amplifying Tome to start. Now keep in mind this is for more advanced players. I then rush Mejai's Soulstealer...I normally get this before I hit 6.

I get Sorcerer's Shoes just because I love magic pen

Void Staff is another huge damage increase

By the time you have gotten the first items you should have enough AP to keep the kills coming and then you can get your big items.

Rabadon's Deathcap is basically a must have for any AP carry. It gives you soooo much AP and works good with your Mejai's Soulstealer

Zhonya's Hourglass is another must have late game. It gives you a ton of survivablity and tons of AP. Use the active in combination with Defile and you can, alot of the times stay alive and get the kill

Guardian Angel is just the icing on the cake. It gives you another go at it while giving you alot of armor and magic resist.

He is pretty manageable seeing as his blinds don't effect you much. Not too much of a threat just have him dancing with Lay Waste
Pretty OP at the moment. Just try not to get in his aoe skill shots or get stunned. Other than that keep him on his feet.
Pretty easy to work with just anticipate the volleys and watch out for level 6 as she will try to stun and kill you
Really easy champ to lane against. If she jumps in just wall and defile, and lay waste spam.
Really broken champion at the moment. She can zone you like no ones business. just try to keep your distance and harass.
Shes really tough. She has an escape and a nuke. Pretty dangerous champ to lane against. Just play safe and farm.
Shes a ***** to lane against. You will have to kill twice keep that in mind and she has the wall which can really **** you. Just farm up while she is wasting time harassing you. Play safe.
Mirror match is pretty easy. As other Karthus' will just try and ult you or half the time not be paying attention. Where you will shine is your farming priority.
As long as you can dodge skill shots you should be fine. And keep out of the laser!
She is not too bad until she hits 6...then...all hell breaks loose. Watch out when she has stun because it will most certainly mean death. If she drops tibbers I normally just counter with flash
Annoying. Try to time your harass until after she uses her Q. She also has that net to which you need to watch out...don't over commit on her. And most of her kills on you...if any will be snipes.
Not too hard of a champ to face. Just watch out for her slow.
Hes a *****. End game if you stacked AP and hes smart...he will make you pay for it. Counter his stun with flash.
Hes more of a one hit wonder. Not a factor until he hits level 6, then you have to respect his combo. His ult will **** up your day so watch out.

Farming is the most important part of being good. If you cant get a good farm you will be weak end game. Last hitting is essential.

Early game- use Lay Waste to take out caster creeps. when those are killed try and auto attack last hit the melee creeps.

Late game- Just use Defile and maybe one Lay Waste and you can kill tons.

Keep up the farm and focus on pushing and farming over killing champs and you will be fed through out.

Always prioritize yourself to mid or a solo lane as your ult is important.

Early game

- Start with the tome and farm up while gently harassing. Keep in mind that you dont want to recall until you have 800g for your soul stealer. Then harass enough and keep them low enough that when you hit 6 you can easily get a kill.

Mid game

- Keep your tower pushed and when it is go help with with other lanes ganking and keep your eye on enemy champions health. From here on out you should just be stacking with soulstealer and farming.

Late game

- You can really punish neutral bosses and keep the gold and buffs coming for your team. you should be buff enough to cause some real damage in team fights.

Ganking is really easy with Karthus if you use this combo.

Wall of Pain> Defile> Lay Waste spam

you can also use flash in combination with that.

If you are ganking from a bush, try to use your Wall of Pain first before anything because it gives you a good advantage because they wont see the slow coming.

Karthus can really shine in teamfights.
You always want to keep your position safe. You never want to be in the fight unless you have to.
So from here you can choose what you want to do.

Option #1
Try to drop your Wall of Pain and hit as many as possible. Then I open with Requiem and brings down the whole teams health. Which makes it an easier fight over all. Then from a distance either Lay Waste. Or go in with defile while keeping my finger on my Zhonya's Hourglass button if it gets too crazy and flash out.

Option #2
Drop Wall of Pain then Lay Waste spam. And keep your eye out for stragglers. If one is getting away either slow him and pick him off or just Requiem them to death. Same as option #1 but you dont open with your ult.

Overall Karthus is a really awesome champion to play. If you want to pick up some easy kills or just have fun seeing people rage hes the way to go.

I will be adding and cleaning up the guide as I go.

Keep in mind this is my first guide so be gentle :D

You can always check out the weekly show called Battle For Middle Lane @ www.theetrium.com. A show dedicated to League of Legends.

Thanks alot guys!