Welcome to my first guide. Everytime I play Karthus, the enemy team *****es me about how I only play for kills. This is not true about me, or more importantly, Karthus. This guide is my personal attempt to show the world how Karthus can play as a nuker and grab those quadras without even thinking of killstealing. I guess this guide is first and foremost, a defense against the idea that all I do is KS.

Now Karthus is an AP mage whomeant for one thing: consistent damage output. Unlike other high AP magi that throw their skills, back away and wait for cooldowns, then throw their spells again, Karthus's role is to enter the clash, gradually wear out the opposition, and finish them off afterwards. This guide will show you just how to fulfill this role.

To start, here are Karthus's abilities. After, I'll move on to tactics.

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This is what makes Karthus so deadly in team fights. Upon dying, he is capable of casting spells for no mana for 7 seconds. This means that even if the enemy team takes you out first, this only dictates that they have lost the chance to use their skills on your teammates. All your team has to do now is make sure the fight continues within your cast ranges, and before the 7 seconds are up, your team will have aced the enemy; at least, that's how it turns out with me. This is the ability from which I drew the conclusion of how Karthus should be played.

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Lay Waste creates a small explosion at your cursor that reveals the surrounding area, and damages enemy units caught in it. If it hits only a single target, this deals double damage. The low mana cost and cooldown means that it is extremely spammable, and becomes useful for scouting, harassing, last-hitting, forcing enemies to step in directions they would otherwise avoid... use your imagination. It also has a respectable cast range. Landing hits with Lay Waste comes with practice.

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This useful little spell that reveals the area it is placed in, slows targets caught in it, and reduces armor and MR. Again, landing this skill takes practice. Oftentimes, a good player is able to slow the entire enemy team with one Wall of Pain, allowing his allies to pick off the enemy champions one by one. While Lay Waste is used to rake in kills, Wall of Pain is used to rake in assists. It is also used for more cautious scouting than Lay Waste, because not only will it reveal the target, but inhibit any affected unit's ability to approach or run.

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Defile, like all of Karthus's other abilities, has many uses. Early game, it is more valued for its ability to keep up your casts of Lay Waste. Later, it is used to rapidly decay enemy hp. With Rylai's Crystal Scepter, this grants Karthus a -MS aura that keeps nearby enemies in check. Sufficient CDR allows Karthus to toggle this on and off repeatedly, dealing damage every time it is toggled on, rather than every second, as said in the description. This is the "radiation" of the nuke that Karthus tries to be. Zhonya's Hourglass works with this ability almost as well as it does with Crowstorm or Slicing Maelstrom.

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If Defile is the radiation, Requiem is the explosion itself. Early game, this serves the purpose of taking out fleeing enemy champions. Later, it serves to deal all its damage at the start of the clash, softening the enemy team for yours. This later purpose is the reason why Mejai's Soulstealer is so valued when I play Karthus. It shakes up the enemy team just enough for them to die when you enter the clash and tap Defile, Wall of Pain, and Lay Waste. Should that not be enough, remember that it's unlikely Karthus is the only one in your team capable of damage. Your allies should finish up your work soon enough.

Greater Mark of Magic Penetration = 9
Greater Seal of Scaling Ability Power = 9
Greater Glyph of Scaling Ability Power = 9
Greater Quintessence of Ability Power = 9

This is the most common rune set I use for Karthus. Greater Mark of Magic Penetration coupled with Greater Quintessence of Ability Power allows me to deal respectable damage early game. Greater Seal of Scaling Ability Power and Greater Glyph of Scaling Ability Power scale better into late game, giving a good 58 ability power.

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Greater Mark of Ability Power
Greater Mark of Scaling Ability Power
Greater Seal of Ability Power
Greater Glyph of Ability Power
Greater Quintessence of Magic Penetration
Greater Quintessence of Scaling Ability Power

These are all good choices for damage. When selecting runes, the main question you ask yourself is: will the game last long? If you believe it will, then Force runes are a better option. otherwise, Potency is the way to go. Insight runes are taken if you feel you can take all the AP you want from items and masteries, and instead need to focus on ignoring magic resistance. Of course, if the enemy team fails to build magic resistance, then you tend to deal true damage when your Wall of Pain is out anyway.

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Greater Mark of Cooldown Reduction
Greater Seal of Cooldown Reduction
Greater Glyph of Cooldown Reduction
Greater Glyph of Scaling Cooldown Reduction
Greater Quintessence of Cooldown Reduction
Greater Quintessence of Movement Speed
Greater Quintessence of Revival

These runes focus less on damage, and so I rarely use them. For CDR, I usually rely on the 20 stacks of Mejai's Soulstealer. Why CDR? Because of Defile. Remember that Defile deals damage upon activation, and every second afterwards. It has a .5 second cooldown, and CDR allows you to toggle it quickly. With 20% CDR, instead of dealing damage every second, Defile chews through nearby enemies every .8 second. By taking other CDR reduction items, the rate at which Defile breaks down opposition is greatly magnified. Greater Quintessence of Movement Speed is an option because of Karthus's slow movement speed. The ability to respawn quickly is also a good choice, as it sucks to be stuck in respawn time when you could have picked up a kill with Requiem.

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Any runes not mentioned, I have no use for. Feel free to experiment, however. I built this guide from experience, and not from watching champion spotlights or reading other guides. This is after all, a guide, and not a rule book.

CORE

Doran's Ring
I open up with Doran's Ring to make up for Karthus's lack of defense. It gives me good staying power, and pushes my AP to 37 at level 1. This isn't bad, for a caster relying heavily on Force runes. It helps with last-hitting creeps with Lay Waste, and builds damage for harrassing as well.

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Amplifying Tome and Mejai's Soulstealer
If you last-hit well enough, you will have enough money for Mejai's Soulstealer by level 6. The reason for getting Mejai's is so that you can begin building AP by using Requiem either for picking up escaping enemies, or dealing damage for an assist when you see an enemy is about to die. If you ask: "Why Mejai's Soulstealer if Karthus will be dying and losing stacks?" If you feel you cannot keep your stacks up, you may choose not to get this. I justify Mejai's Soulstealer because by late game, I often do not cast Requiem while in my spirit form. I will discuss this in a bit, but for now, note that this tactic means I am almost always at 20 stacks when casting my ultimate.

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Boots and Sorcerer's Shoes
Sorcerer's Shoes are the only real choice of boots I use with Karthus. The reason is that I want to deal as much damage as I can early game with my ultimate. It tends to be a big factor to have a base 30 MR to screw up Requiem's damage output and save enemy heroes from early kills.

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Blasting Wand, Ruby Crystal, Sapphire Crystal, Catalyst the Protector, and Rod of Ages
Rod of Ages is taken because when it grows to full power, it gives as much AP, and more hp than a rushed Rylai's Crystal Scepter. The mana and hp regen per level-up is also quite useful, and the mana bonus works wonders with Karthus's role of dealing sustained damage. If farm is good, I get the Blasting Wand first.

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EXTENSION

Zhonya's Hourglass
I take this item after my core about 90% of the time. The ability power is good, and so is the armor. The real purpose of the hourglass is the Stasis ability, which buys Karthus additional time to wear his enemies down with Defile. Used offensively or defensively, the 2 second difference often means 600 points of difference from all enemies dumb enough not to back away from you. If they do back away from you, then who knows? Maybe you'll even be able to make it out of a tight fix.

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Rabadon's Deathcap
There are games that don't last long enough to finish this item, but in case your team cannot capitalize on your sheer AP before you complete this, then you might as well build it. This forces your AP beyond reasonable limits, and can allow you to grab kills with Requiem incredibly early in team fights. I've personally seen softer champions drop dead from 40% hp with a single cast of Requiem, and that was without Executioner or a full rune set.

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Rylai's Crystal Scepter
Simply because Karthus is slow, you might as well pick this item to slow enemies to your pace. It works with Lay Waste, and deals additional slow if you hit it as a single-target nuke, and it works with Defile, slowing the entire enemy team. The 500 bonus HP is also nothing to regret, and 80 AP gives you more damage. Be sure to check if you need it though. Rylai's Crystal Scepter is addictive, but might take up good inventory space if your opponents call for situational items.

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Void Staff
This is another addictive item, but is not always recommended. 70 AP is outclassed by a lot of other items, and 40% magic penetration is not that useful in games where the enemy team doesn't build up MR items. If you find yourself facing off against tanks however, this is a good idea.

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Abyssal Mask
This is another anti-tank item. It scales well with Sorcerer's Shoes and Wall of Pain. Be careful though. Since this is not Magic Penetration, your Requiem will not benefit from the damage amp if the enemy strays too far. The advantage is that your allies will also deal better damage. It might be better for another AP champion, such as Katarina to take this, but if the situation calls for it, then go ahead.

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Deathfire Grasp
This is a situational item used against champions with raw HP, ergo Sion, or soft champions, ergo Vayne. In the first scenario, this greatly weakens Sion's ability to tank. When this happens, your team of course, takes him down. In the second scenario, it just kills Vayne before she can kill anyone else. Remember that because of your sheer AP, this will remove almost 50% of any opponent's remaining HP. By running away and casting Requiem immediately after Deathfire Grasp takes its toll, you deal respectable damage to the entire enemy team and wipe Vayne off the map.

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Archangel's Staff
This is a great item for Karthus, but it is an even bigger gamble than Mejai's Soulstealer. First of all, the base AP is not that good, and second, because you need to cast a lot to get that 1000 mana cap. This isn't a problem, but there are faster ways to increase your AP. If you must have the mana and AP bonus, take Tear of the Goddess early game, and finish the staff late game. Rushing the full Archangel's Staff from the beginning is just too big a risk to take, and will not guarantee a burst of damage from any of your skills, even with Surge

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Other mentionables are:
Banshee's Veil sacrifices offense to gain much needed time on the battlefield.
Will of the Ancients works wonders when regenerating with Zhonya's Hourglass active.
Haunting Guise is an early game item for additional MP.

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Regarding unmentioned items, I just don't see the purpose of them, but try to experiment.

This is the primary ability sequence I use with Karthus. It maximizes my damage output with Lay Waste ASAP, gives me a level of Wall of Pain which I find sufficient for its slow, and incredible mana regeneration and extra damage with Defile.

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I sometimes do this if I find my allies are more than capable of killing, but lacking in a good CC ability. This maximizes Wall of Pain's slow, allowing allies to pick up kills every time you gank. The downside is that your own damage output is not that great until late game, and you will have to rack up on assists to gain stacks of Mejai's Soulstealer.

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This one I rarely use, though I have relied on it once. It is a balance between the first two builds, and usually is the result of having to adapt to a good enemy team countering your initial play style. This is not recommended, but may be necessary at times.

VIABLE


Ghost and Surge are my most valued Summoner spells. I know you're probably thinking: "What the ****? Surge? How can Karthus make use of the AS increase?" I can see your selling point, but here's my defense.

I choose Ghost because of my lack of mobility. Half the time, a well-timed Ghost can spell the difference between a kill and a missed opportunity. It is capable of chasing champions who get overconfident with Flash or some other high mobility skill.

I choose Surge of course, for the AP increase. The burst of AP from Surge works naturally well with Karthus if you play him the way I do as a consistent damage over time dealer. By tapping Surge upon entering a clash, Defile and Lay Waste enjoy significant increases in damage. Because of the increase in AS as well, Karthus can let loose a few normal attacks in between taps of Lay Waste. Ignite grants true damage that can be fatal, but will only be useful on a single target. Karthus is not a single-target assassin.

Also, if you think that the AS is useless, well so is the AD from Ignite, but you don't complain there.

Flash is of course, viable for anyone. I just do not see it outclassing Ghost's chasing and escape ability in any place away from walls narrow enough to Flash over. Since most clashes and team fights take place in lanes, Ghost tends to close the gap made by flash faster than most enemies can run. If you choose to get this, you might as well take Summoner's Insight to back it up.

Clairvoyance is good when you want to be sure you can kill fleeing enemy champions, and feel the need to look at their remaining hp. It is also a viable scouting tool. Of course, if your team uses wards, this isn't as necessary.

Cleanse buys you extra time before dying, and can waste a lot of Ignites and CC abilities.

Teleport is just really handy for mobility, though you have to have an allied target.

What the fuuu... Revive? I know, I know. This is not something I don't normally get, but it has utilitarian purposes, like catching enemies off guard with Requiem when they think you're still respawning. The bonus MS from Summoner's Resolve is also great for preparing yourself for another clash. Still, I don't really pick it up that much.

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NON-VIABLE


While Heal can be useful, it loses its usefulness the more games you play. The same is true for Clarity. Karthus can't really use Heal to pull his hp back up and buy time to keep up his Defile, as in a team fight or gank, he most likely will have Ignite on him. He doesn't need Clarity because a single Doran's Ring makes up for his mana consumption early game.

Ignite and Exhaust are in general, good choices for any champion. The downside of course, is that you gain much less AP than from Surge, and there isn't really any need for Karthus to carry this, since your team's assassin or fighter, or maybe all of them will have either or both of these spells.

Smite is taken by the Jungler Karthus. I do not like jungling, so if you want to take this, go ahead. I'm not, since my lane control is usually something I do not like giving up.

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Remember, I play Karthus to wear down the enemy team, not to guarantee killing only one of them. That is a job better done by nukers like Veigar. In reality, a lot of summoner spells are viable for Karthus. I just mark them as non-viable because while they work, they do not seem to fit his role the way I see it. Feel free to pick whatever summoner spell you're more comfortable with.

This guide is the general concept of how I see Karthus. I'll try to place the pros and cons, teemwork, and advanced tactics later on. For now, tell me what you think. I know I'm bound to get negative criticism, especially for the out of the box idea of choosing Surge over Ignite. Still, I'm open to suggestion. If you doubt this build, try it out. Try playing Karthus the way I do, and then vote. I'll also ad some pics, maybe, and I'll add other stuff to show how this really works.

For now, I've got to eat.