Hello, dear reader, it has been a while since I used my Mobafire account, and since I updated this guide...

This is my Karthus guide that did not fail me when I needed it, and it should not fail you if you are going to use it, and know how to play.

Karthus is an easy champion to play, and a bloody hard one to master.

1. Buy starting items, and then go mid.
2. Wait for minions and farm with bothand basic attacks.
3. Whenever you see a clear shot on the enemy laner, use both your and basic attack followed up with another to harass, that way, you are going to deal quite some damage, and get some free damage, on them while waiting for to come off cooldown.
4. Always chill, do not get upset if you miss a cs, if you teammate dies... Who gives a... The point is that you are playing Karthus, and that you can carry the game(most likely) if the enemy team is not brutally fed whilst your is at 3K gold in minute 15...
5. Do not worry about dying too much, especially in teamfights, go in, cast your Wall of Pain on the enemy carry and support, that will debilitate them and make it easy for you to hit them with .
6. Use Zhonyas Hourglass when needed to survive and deal free damage with E to enemy team in a teamfight, because 2.5 seconds of interrupted damage on 3 to 5 people is a very good thing for your team.
7. Always try to get as much objectives as possible, regardless the game phase, if you can get a tower, get it, if you can force a Dragon, do so! Kills mean a lot, but I have seen teams with 40 kills that lost to the team with 20 kills, just because the 40 kill team had much less towers and much less gold overall!
8. After you die, cast 2 or 3 depending on your skill and ability to use the Lay Waste ability, then cast Karthus's ultimate to do the maximum damage to the enemy team. If you lost the fight completely, think about is it a good idea to use the Requiem or should you save it for kill sniping later on when you respawn!

Also, TIMING!

Time is everything with Karthus, including the ability to kill someone.
Time your ultimate, never rush it or u will waste it, and it has a bloody long cooldown!
Time your movement, you can get killed in 0.1 second with Karthus.
Time everything!
Zilean has a clock on his back, I suggest you to buy one and put it in front of your face.

Marks:Greater Mark of Magic Penetration- .87 Magic Pen x9
Marks result in 8 Magic penetration points. Those do not need any explanation. More damage, and they are in the same time the only viable runes that you can get for Red section.

Seals:Greater Seal of Scaling Ability Power- .1 Ability Power/lvl x9
Seals result in moderate amount of Ability power in late game, 17 to be exact. That is not much, but since you have Defile to restore your mana during the laning phase, you do not need mana regen, nor do you need Cooldown Reduction, because Seals give almost no Cooldown Reduction.

Glyphs:Greater Glyph of Scaling Cooldown Reduction- .09% Cooldown Reduction/lvl x9
Glyphs result in moderate Cooldown reduction of 15% at level 18. That amount of Cooldown reduction is significant enough to impact your ability cooldown and since you are not going to get the , because it is mediocre. A powerhouse like Karthus needs extreme stats that make him strong, not mediocre!

Quintessences:Greater Quintessence of Scaling Ability Power- .43 Ability power/lvl x3
Quintessences result in 23 Ability Power at level 18. That combined with Seals is going to give you 40 Ability power, which is quite a number for Karthus's set of 3 AoE abilities.

21:0:9

I am not going to explain every mastery nor am I going to tell you why should you take those, I believe that you know why are you using those masteries. I mean seriously, every single author explains why are they using offensive masteries on a mage, combined with utility mastery branch. I know that some use it to drop in few drops of humor essence while explaining, but this is not a humorous guide, you are here to increase your win rate, not your smile per day rate.

Offensive branch of masteries are used to increase your damage to the maximum.
Defensive are not being taken because you need damage, not health or defensive stats.
Utility branch is there to increase your performance by boosting your speed, so you can place morebeneath your enemy's feet. Also it will increase your buff duration since you are going to kill the enemy jungler and take his blue buff whenever possible.

This guide is made for ranked games, so I am not even thinking of naming mirror lane or anything like that. I hope that you have at least some experience with Karthus and know how to farm, use spells, gank, ward, steal stuff and beat people up to take their wallet.

So, to continue, you entered a game, you probably played 5 games before this one and you got ****ty placement in pick selection and were unable to play Karthus. Now, this is a new game, clear your mind, take a smoke, or resume with chainsmoking like i do for 8 hours when i play(I once did, now my gaming is very rare but i still follow the game of League and know more than probably Morello does, since i devoted 5 and half years of my life to the League and i played it with burning passion and love. I studied every champion for months so i can go against them, that says a lot about my mental state...)

Now lets continue after my little biography, you are in the spawn pool, you bough your faerie charm and 4 mana regen pots and 4 health pots. Go to lane, and wait for minions behind the tower. Once they arrive, as i said, farm with both Lay Waste and basic attacks, and when it is possible to harass without being punished do so.
Your goal is to farm like Nasus and not slack while doing so since you are much less tanky.
After you are at about 900 gold which is just few minutes in, about 7th minute, go back to base, buy the Tear of Goddess and cloth footwraps. Go back to the lane, you have the scaling ability power runes that augment your spells so you do not actually need a lot of ap currently. Return to power-farming, try to stay safe and call in for ganks when