Hi guys!

I am D o n garang (without spaces) and I play on Europe West. At this moment I am the #84 Karthus in the world and I decided to make a guide for him since I know him quite well. I am in Diamond 5 and planning on climbing to master or even challenger this new season! I have started playing Karthus since season 2 where PhantomL0rd trolled with him and ran TP & Revive. Since then I fell in love with the champ. I have played over 1000 games with him over 4-5 different accounts with an average of a 70% winrate. I have studied Karthus after PL's stream and mastered him. Right now, it is your turn!

Karthus is a low mobilty, high damage output champion who can burst people down in seconds. (If played right.)

Let us start with his passive.

Passive / Death Defied

"Upon Dying, Karthus enters spirit form that allows him to continue casting spells for 7 seconds."

This is one of the reasons why Karthus is overpowered. Even when you get killed in team fights, you still have 7 whole seconds to continue casting spells and trust me. They hurt.

Q / Lay Waste

"Karthus unleashes a delayed blast at a location, dealing damage to nearby enemies."

One of the strongest abilities in-game in my opinion. If you hit Lay Waste on a single target, the damage is doubled. That is why he can poke and burst champions quickly.

UPDATE:
Since patch 10.16 the AP ratio went from 0.35 to 0.3. This only affects the late game a little bit, but not that much. He still is a valid pick.

W / Wall of Pain

"Karthus creates a passable screen of leeching energy. Any enemy units that walk through the screen have their Movement Speed and Magic Resist reduced for a period."

This ability is amazing. No matter how much magic resist the enemy has, you can always damage them in combination with Sorcerer's Shoes, Void Staff and Morellonomicon.

E / Defile

"Karthus passively steals energy from his victims, gaining Mana on each kill. Alternatively, Karthus can surround himself in the souls of his prey, dealing damage to nearby enemies, buit quickly draining his own Mana."

Great ability to sustain in lane! The Mana you get back after killing a unit is +- enough for 1 extra Q. In team fights you must activate this ability and keep it activated. Only turn it off if you are low on Mana. I would not recommend turning this ability on in early game since it will drain out your Mana quickly.

R / Requiem

]

"After channeling for 3 seconds, Karthus deals damage to all enemy champions."

An ability that deals 250 damage on its first level to all five players at the same time. This is a game changing ultimate. In combination with your magic penetration you can basically deal true damage on carries in late game. You have the possibility to one-shot them.

Don't use your ultimate just to secure a kill. If your bot lane gets ganked by the enemy jungler or your mid laner, activate it! There is a high chance that the enemy team will back off since you dealt a lot of damage to them. This way you saved your bottom lane and maybe secured an assist for yourself! Or you can use it when you see your top laner / bot laners fight. Either way, teamplay is important!

This season Karthus is all about dealing high burst damage AND DOT damage. That's why Liandry's Torment is important together with Demonic Embrace. So the runes stay the same!

Abilities wise, you should always start with your Lay Waste. No questions asked.
Your second ability should also be a no-brainer: your Defile.

From now you got an option. You can put a point in your Wall of Pain but only if you know that you can get a secured kill out of it. Or if your jungler does a level 3 gank. If this is not case, put a third point in your Q Lay Waste. The damage boost will reward you anyway.

Now on every single skill point should be placed in Lay Waste, followed up by Defile and at last Wall of Pain. Your ult Requiem on level 6,11,16 of course.

There are a lot of options for Summoner Spells.

Flash is a must on Karthus though. But your second Summoner Spell slot is customable.

The first option is to pick Exhaust. I would recommend this when you're playing vs an assassin champion just like Zed or Talon. The slow will also help you land your Q's better.

The second (and last) option is to pick Teleport. This way you will not miss a lot of farm. There is no real other reason to pick this Summoner Spell.

Just like every single champion, Karthus has some strengths and weaknesses.

Pros
+High Damage
+Global ult hitting all enemies at the same time
+AoE damage
+Has CC (Crowd Control)
+Even when you're dead you can participate in team fights with your passive
+Strong early game

Cons
-Squishy
-No mobility
-Gets countered by a lot of champions

After experimenting with a large item set, I've found out that buying ]]Liandry's Anguish]] in combination with Rylia's Scepter and Horizon Focus one of the strongest combination of items there is.

These items provide you with a less duration Twisted Fate ult ( Destiny) that also deals damage, slows the enemy down and applies a DoT on them that prevents them from recalling, proccing Warmog's Armor's passive etc.

However, with this seasons' new items, Malignance, Luden’s Companion and Stormsurge form a great set of items to instantly buy as early as possible.

When the first creeps are in lane and when they are fighting each other, use your Q Lay Waste on the caster minions (single hit them). Do it until all 3 of them are dead. This way you can push your wave and try to poke the enemy mid laner down. Try to deny him experience and cs as well. In all cases you shouldn't use your Q Lay Waste on multiple enemies, only if you can kill them all at the same time with just one Q Lay Waste.
Try to take the raptors as well after you've pushed your wave into his turret. A little bit more farm is always welcome.
As soon as you reach level six, you should look at top lane and bottom lane to look at the enemy players their health bar. Maybe you can secure a kill.

In team fights you should be the one who initiates. Since you have your Zhonya's Hourglass in combination with your other items, you should be good to go. But before you go into your Hourglass, don't forget to activate your E. It's literally free damage. Don't use your ult if you're alive in the team fight, leave if for when you're dead. Don't use it too quickly either, try to land some Q's and try to time your ult.

Al right. Let's top it off by saying that Karthus isn't viable in every single ELO. In higher ELO's he will be countered and outplayed 95% of the times. Hitting your Q's will be a real pain in the *ss and you will probably get one shotted by the enemy. In lower ELO's (plat 2 and lower), he is an overpowered champion. Most of the players do not know what to build or rush against him. Try to use that to your advantage.

If you have any questions, go ahead, and ask me in the comment section! You can also add me on League of Legends too! My in-game name is Ding Dong Gaming.

So far I've been doing great with the same build as I've shown you guys in my guide.
I ended up in Platinum 2 with a 8-1 win ratio with

Karthus

These are my statistics so far.