Tips for building karthus
i Love he's R is there any tips for like items and stuff for him?

i Love he's R is there any tips for like items and stuff for him?

As a Karthus player, these guys all know their stuff. I would like to explain why I think you should get each item they say and which ones in which situations:
because each one of your spells (which you use all of the time) gives you extra maximum mana.
because of the speed and magic penetration.
because of the ability power, mana and health.
that transforms to
as the extra ability power stacks with your extra maximum mana, and the shield is always helpful when engaging or disengaging in a fight.
for when you get focused in teamfights.
is an amazing item in my opinion for
as he is able to double his E as a slowing aura, make his W mega-slow enemies where they can almost not even move, and all of his Qs slow, allowing him to catch up to anyone he hits with any of his abilities very quickly.
for the extra ability power.
for the extra magic penetration.
I would recommend this be your build order:
>
>
>
>
>
>
>
>
>
> 
So your final build should be something like this:

Sometimes certain items may be situational or you may want to build these items in a different order but as long as you get the general idea you should be fine.
in no particular order:

Nomicon for the cdr zhonyas for AP, armor, and active deathcap for extra AP void staff for more dmg (and for mr users) DFG for Ap and active AA for mana and more AP
You really shouldn't get
unless they're full of healers. Most of your damage comes from your Q and you can easily finish enemies off with your R. Just wanted to point that out. Get
for more Qs and overall more damage and safety.
Do not go
. Sure it makes your R do tons of damage but you'll die instantly. You may think but my passive! Sure your passive lets you do like a couple more shots but being alive means more Qs in the long run.
A typical build is
- It gives health, mana and AP. The health helps you when you go into a teamfight and do damage with your E and the passive heal helps you if you're struggling in your lane.
- This synergizes so well with your E. And when you go into teamfights it works with your Q too. And the MR helps you survive against AP bursters and works well with your Seraph's shield and RoA health.
- More AP = more damage.
- It gives you the mana to spam, the shield helps you to survive when you go in with E on and it synergizes with your
.
- The magic pen helps you do more damage and movement speed helps you dodge skill-shots and get into position for more Qs.
- Gives armor which works well with the RoA health and the active is great when an assassin like
tries to kill you.
And remember that this is just a generic build. You should always change the build based on the enemy team. If they're full of people who have no dashes and full of movement speed buffs then consider getting a
for the slow.

/
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Something along those lines is standard. The last item is situational, but I'm personally a fan of either Rylai's or Zhonya's.
know a build for one shoting all 5 champs? xD
if you really only want to one shot everyone one 20 stacks on

you either want to rush
or
as your first items, bc you need the mana. After that rush
and
, after that it's typical AP mage build. Just remember that there is a LOT of incentive to go full AP, so don't fall into a tanky AP trap (if you are mid, at least)
Current typical high ELO Karthus cookie cutter build:
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The High elo's stopped building RoA on Karthus a while ago, but I don't think most people have caught onto that yet. It used to be a point of debate, but then Rylai got buffed :/
BTW, the last 3 items are in no particular order.
deals the most dmg in general
is a must if they have a lot of MR
is the strongest teamfight item in general, and the stasis synergises with Karthus' E.
The High elo's stopped building Rylai on Karthus a while ago
I assume you mean RoA? Cause if so...
http://www.probuilds.net/champions/Karthus
Disagree.
Even with the changes to Rylai's, RoA still simultaneously offers more tankiness and more damage, and its build path is a lot better for laning.
Yes, I did mean RoA. Thank you for that correction, I edited the post you replied to ^_^
Rylai definitely deals more damage than RoA. 100 AP vs 60-80 AP, AND the slow lets you hit your Q's more consistently, which is you main source of dmg. RoA does offer more tankiness when it's completed, but during the item pathing the Giant's Belt actually offers 2ce as much health as the Catalyst. Both items have really accessible build paths if you ask me :/.
As far as builds go, I tend to focus much more on champion mains than on pro's. Pro's play a very different game (premade 5es against other pro teams) where different things become important. That and not all the pro's listed in your link are mid mains or regular Karthus players. Some are though, so this is interesting to see. However, when it comes to soloQ I believe more in the build paths and strategies of actual soloQ mains of that champion. Here are some: http://na.op.gg/summoner/userName=King+Ninjakramer http://na.op.gg/summoner/userName=Azingy http://na.op.gg/summoner/userName=God+Karthus+NA http://na.op.gg/summoner/userName=Plun http://euw.op.gg/summoner/userName=inojlol http://euw.op.gg/summoner/userName=Krisz+Kik+Essz http://euw.op.gg/summoner/userName=DionysiusL All D1/Master/Challenger players who play a crapton of Karthus and essentially follow the buildpath I offered there...
Now, re-researching it for this thread I did find that RoA IS built on Karthus sometimes by some D1 European players (like the last guy I linked). Interesting to see :/.
Rylai definitely deals more damage than RoA. 100 AP vs 60-80 AP, AND the slow lets you hit your Q's more consistently, which is you main source of dmg. .
RoA gives 93 AP when you take into account the passive on Seraph's embrace. But yeah, I do think that Rylai's is a really great item on Karthus - just not necessarily worth skipping RoA.
during the item pathing the Giant's Belt actually offers 2ce as much health as the Catalyst. Both items have really accessible build paths if you ask me :/.
The difference is, Giant's Belt is a much worse laning item than Catalyst. Consider that after a single level up, Catalyst is offering you just 30 less health than Giant's belt - after two level ups, not only has it provided you with 120 more health in lane, it's also given you 700 mana. That's ~25 extra Qs that you can get off in lane.
If you're a low level Karthus that just wants to farm from a distance, Catalyst is gonna do way more for you than a Giant's belt.
As far as builds go, I tend to focus much more on champion mains than on pro's. Pro's play a very different game (premade 5es against other pro teams) where different things become important. That and not all the pro's listed in your link are mid mains or regular Karthus players. Some are though, so this is interesting to see. However, when it comes to soloQ I believe more in the build paths and strategies of actual soloQ mains of that champion. Here are some:
Those builds are drawn from soloq games exclusively. Whenever a pro plays Karthus on their main or a known smurf, it gets recorded there. So, when Faker, Froggen and Alex Ich build RoA, they're doing it in EUW/KR Challenger against soloq players. And doing rather well for themselves, last I checked.
I take
and
for full cool down with the 5% from masteries

I don't like tear takes to long to be useful also rod of ages is sort of like tear you have to wait for the power
were as you rarely go oom with Athens and u get mr and cool down with the ap
exaughst is good against those ad mids like zed and yasuo flash is a obvious choice teleport or ignite are good instead of exhaust

,or
, or 
My build :
first item
second item


Rabadons cost too much to be effective.
no one is mentioning the global slow on the ult
Try this....
....it didnt work for me lol, but try it