Hey there mobafire! My names Ethan and this is my first mobafire guide. Il start off by saying i am not an experienced level 20 pro player. I am a guy who plays this game for fun but hates losing and loves killing people. I looked into other Karthus guides and i was generally disappointed with my scores. I tweaked some things here and there and have created a build that i do pretty good on. And without further ado here it is.

The masteries are pretty straight forward. Offense is for power. Power = kills. Now for utility. I put skills in there to increase the mana pool so i can use my Q and E more. I hate when my R is down and i dont have enough mana to get the final blow with my Q or run out of mana in a team fight with my E. Time spent dead is in there because karthus is known to be a suicidal double, triple and even quadra killer and i like getting back up faster when i die.

Quintessence on Ap for Power and damage.

Seal on Replenishment to get more Mana Regen. Helps a ton for farming

Mark on insight for magic penetration. Helps a ton for killing em off with your R

Glyph of force to get get more AP at a higher level to boost your Q ,E , and R

If you want to be a good Karth, you need to get fed. In order to get fed you always need to be ahead of your opponent in minion kills. 10 minion kills = 1 player kill worth of gold. Use your Q to finish off minions to grab the gold. Try to only hit one minion at a time to deal 2x at early levels in order to not run out of mana. In order to be good at farming you need to "zone" out your opponent. You need to harass your opponent with your q making sure you lead him into it. You want to make him B and you want to stay in lane as much as possible. Beware of ganks though.