I've had much success with it, but ok.

@Geronimo: Yay for troll votes.

Because of teleport

utility spec much better :< tried this one out and failed miserably over and over

Not bad at all

Above

I've both tried this build/guide, and seen it used. I can honestly say I've seen very few guides that are as effective in explaining EXACTLY how to use his skills. And as far as teamfights go this build DOES mitigate karthus away from suicide bomber to imba-DPS.

Personally I don't use the CDR runes (I use magic pen in blue). Simply because his Q doesn't profit quite as much as other spellcasters (his ulti does though).

All-in-all an excellent build.
:]

Personally I prefer to stay alive longer, as it lets me get more damage out in the long run. To paraphrase another guide I read on here, if you die you have 7 seconds on a fixed spot - if you're alive you have as long as you can stay alive to do damage. On top of that, you can continue moving. My build ends me at 3.1k hp, assuming you have elixirs, and 3k-3.5k mana. I find this is much better than the standard 1.8-2k or so, as it lets me not melt in teamfights - you don't have to be a suicide bomber, just a massive AoE damage output.

I hadn't thought about getting the teleport mastery. I'll try it sometime! I also get Void Staff sometimes, but it really only helps for taking down tanks. I find the 15% from masteries is enough to keep your damage output steady throughout the game on the people you need to be killing.

To everyone asking why WotA is my last item on the list: Please read my items part of the guide. I explained why it's on there and when you would actually get it. It's NOT an item I get often, but it is good for healing against a strong early game harasser.

To Deathalo44:

I realize the CDR is pathetic, but it's more useful to me than MP/5, as with this build you don't NEED the MP/5. A fast tear along with your E's passive gives you all the regen you need. If you find yourself running out of mana on Karthus, learn to last hit better. That's where his mana comes from.

I don't understand what you mean by my build shown and build explained being different?

Tankiness is bad for Karthus? How so? Going straight AP, as I said earlier in this mass-reply, causes you to melt most of the time. I still receive ALMOST the same amount - above 850 if I replace my Zhonya or Rylai's with a second Archangel. You stay alive much longer and therefore deal more damage.

Demordir:

That's a good point. I don't really itemize towards it, since the 9% or whatever it is I get from runes and masteries seems to be enough. I'll try 9/0/21 for the CDR, but I don't really like the idea of it. The fast ult is great, but I think the extra 100 hp early game plus the resistances and such are much more useful. But I will try it for a few games!

Sorry about the wall of text, if you have any suggestions on what I can improve, please let me know!

See above

Greater seal of focus has pathetic cdr, and should be replaced by mana regen. Your build shown and your build explained are different (namely 9 21 0 and 21 9 0 or 21 0 9 respectively). Getting above 9 for ANY pure spellcaster is useless, most of it is just boosting your damage, the only one being decent is the final one which gives higher overall damage. Tankyness is very bad for karthus, meaning you have less time to get your AP goodies as well as the fact that they do very little for you after early game. Will of the ancients is kind of useless seeing you probably will not have high enough hp to regen good enough (Just like a glass cannon TF not getting lifesteal since he probably dies before it actually works).

Hope it helps

WotA as a final item. Whatt

nice itembuild, nice guide...good

Voted