Good guide! But I saw a video about Karthus with 4 Rabadon's DeathCap and he was with 1017 Magic Damage, so I'll do some changes in your guide while playing...

Great guide, have not lost a match with Karth yet (9 matches, 1 ranked) I have gone soulstealer every game after sorcerer's shoes and gotten 15+ stacks every game. His Q HURTS.

This guide creates one of the most powerful possible Karthus and also, the title is a nice touch along with very elaborated content.

I have used this build time and again and (almost) always win, of course, some of my success is contributed by my natural talent in AP champions, even still, this is the guide you want to be following if you want to play well (of course, skill is one limiting factor to absolute power).
+1 for you.

P.S. I even created an account just so I could give much praise to this almost, if not, perfect guide.

Used this build for "Kamikarthus", run in with ur E on, use the hourglass, die, 2 balls, ult and then 1 ball. Defnite triple kill at least :)

Nice guide!

I loved the build I tried my first game ever as Karthus and used this build and went 15/0/14!

little warning...i had to face a premade team with random fails on mine..soraka was mid against me..omg that zoning was rediculous.but anyhow good guide and your masteries/build is alright.end game score was 9/8/13(i was only person with positive score on my team. -_- ).

I tried both 21-0-9 and 9-0-21 and I like 21-0-9 more, since you have this mana regen from your passive. Good guide though.

great built plus 1 for you. i have been using this build for quite awhile. after awhile i realise that rushing rylai skepter was good the early extra health mana and slow really assisted me in mid games.

recently i tried another item build. first item rush after boots and tear of goddess is deathcap after that i rush tear of goddess to archmage angel staff. then i stack 3 more onto it.

what do u think about this built? wanna hear some comments from you.

its better to go RoA then archangels :p

This build is really good and it helped me alot with leaning/mastering karthus but have you ever though about masteries 21/0/9 ?

-1
Where to start... I did not like this guide, and I think there are better guides out there. I dont understand why this is #1 on mobafire.

I would'nt recommend starting with Mana Crystal, because I think its better to use Boots in order to easily avoid skillshots and get an additional hp pot to start with (better sustain). I also dont think you need to start with a mana pot at all, better get all hp.

Building Tear will make Karthus very fragile early game, I think Rod of Ages is enough to satisfy his mana the whole game. Archangel's staff is a bad item too. Dont get it, because there are better items.

Finishing the build with both Abyssal AND Void staff is counterproductive, since they dont support each other well at all (% spell pen is calculated after flat spell pen).

Last, but not least, I would pick Defile before wall of pain almost 100% of the time, since it helps your mana regain and lasthitting potential. It is good for lasthitting, since you may toggle it on/off instantly to deal 1 tick of damage to nearby creeps, if you need to.

Edit: I also find it weird that you would go with utility masteries on Karthus, since he benefits ALOT more from having specced into offense.

Btw, you Exhaust is barely mentioned, even though it is a great spell on Karthus. It makes landing your Q easier and makes him win 1v1 fights easier. Since he deals SUSTAINED damage, it will also many times be better than ignite. Obviously also a useful escape mechanism, since his Wall has 18 sec cooldown.

Realy nice guide! Been playing with Kartus a few games now and this guide realy helped me out.