I know I didn't finish my boots or itemization in the main picture. Read the guide and you'll understand. that is just my core build.

DO NOT KILL STEAL WITH Requiem!!!!!

enjoy the guide! :)

Best Ranked game as karth so far: 11-4-9 or 8-2-5 (20 min surrender)
Best normal game as karth so far: 16-4-5 (20 min surrender) or 26-9-28 (quadra/baron steal)

Hey guys, this is my low Elo Karthus guide. It's only my second guide, so constructive criticism is appreciated :)
I decided to make a Karthus guide because I love the champ. I play him all the time in regular games, and average 17 kills per game. I decided to play around with him in ranked, and wasn't upset with the results.

enough rambling, time for a guide!

for runes I go with the basic AP carry setup. 9 Greater Mark of Magic Penetration 9 Greater Seal of Ability Power 9 Greater Glyph of Ability Power and 3 greater quintessence of potency. this setup gives you about 29 starting AP, and like 9 MPen.

I do this because I don't build any AP until mid game. That's also why I take the Burning Embers mastery over the Tenacity mastery. feel free to change the masteries, this is my personal setup so I have decent level 1 survivability.

Ignite for the extra DoT. I get plenty of early game kills through spamming Q, flashing, igniting, and then walking away. great for slamming champs like Vladimir or Soraka, because it reduces healing.

Flash because it's Flash. great for escape from ganks, positioning, showing off, whatever.

other possible summoner spells:

Teleport good for getting back in lane.
Exhaust if you have to go against a lot of AD champs, or your team needs CC
Clairvoyance. if you aren't sure whether or not your ult will get the kill, CV on them and check their hp and mr. takes skill for placement, and is getting nerfed soon.
Heal. its kind of gimicky, but you can bait someone when you have low hp, heal, rape, and if they do kill you, you have Death Defied for the finisher. I dont like heal personally, but it can work.

Never get:
Revive
Rally
Smite
Fortify

the ones i didnt mention are kind of whatever to me. use them if you want. I dont c

Items are kinda straight forward.

your core build is: Archangel's Staff Rylai's Crystal Scepter Rabadon's Deathcap and Zhonya's Hourglass. You also need to get Blue Buff as often as you can. you need boots, but we'll talk about that later.

start with Sapphire Crystal, a Health Potion and a Mana Potion, so you can spam your Q even at level 1. build an early Archangel's Staff (you should have it around level 6 if you farm well, but don't get any kills. if you get kills, enjoy your 140 AP at level 4)

If you are dominating mid lane (which you should be. you're effing Karthus) then go back as soon as you have enough gold for Tear of the Goddess. That way you start getting mana really early on.

The rest is simple. Needlessly Large Rod if you farm well. otherwise grab your Giant's Belt and get an early Rylai's Crystal Scepter for the slow, survivability, and AP.
finish the core build in whatever order the game calls for. sometimes you want to nuke. so go Rabadon's Deathcap right after your Archangel's Staff, then Zhonya's Hourglass. if you're more of the DoT Karthus you'll need the survivability of Rylai's Crystal Scepter and Zhonya's Hourglass

I only listed 4 items in this build. Thats because no two games are alike, and you'll have to adapt to their team. sometimes you can stack Rabadon's Deathcap and sometimes you need to get tanky items ( Banshee's Veil). Just use common sense.

BOOTS
there are 3 viable options for boots. if you're going tanky/ they have a lotta CC, get Mercury's Treads
if you're going for nuke: Sorcerer's Shoes
if you're going for a lot of ults/ Q out the butt: Ionian Boots of Lucidity

other viable items on Karthus: Will of the Ancients, Rod of Ages, Abyssal Mask, Mejai's Soulstealer, Void Staff

Q Lay Waste Karthus actual damage doer. unlike popular belief, Karthus is not a 1 click champ. Lay Waste is what you use for harass, farm, damage, everything. I get this at level one and max ASAP.

W Wall of Pain. This is a handy move that is good at blocking escapes. I get this at level two, then leave it alone til late game. (I sometimes get an extra level or two for the MPen, depends who im against)

E Defile. This keeps you in lane. Use the active sparingly, because it drains your mana fast. very nice with Zhonya's Hourglass active and Flash.

R Requiem. what makes Karthus stand out from the rest. This is a high damage universal Ultimate with a long cooldown. Use this to kill secure, NOT TO KILL STEAL. Although it does crazy damage, and is universal, it is easily countered. Remember, always try to check a Champs HP and MR before you ult. just cuz they look low doesnt mean you can kill them. Play intelligently.

Negatives to KS'ing with Requiem:
You put your ult on CD, which means you won't have it when its needed to secure a kill.
you steal gold from someone who earned the kill.
you piss your team off, leading to reporting, ragequits, trolling, etc.
you probably lose the game for your team, you selfish noob.


how to use your powers in game:
early game: you simply farm/harass with Lay Waste. when they're low, Flash in, Ignite and throw up the wall to block escape. If before level 6, make sure you land your Q, and Flash AFTER they Flash. if you have Requiem ready for use, let them flash away with nothing, and kill them anyways. It's very satisfying.

Mid game: get Rylai's Crystal Scepter soon. the slow with your powerset almost guarantee's that you will get kills. Just be ready for ganks. If a teamfight breaks out, pull the strings from the backround. Ult people who flash away with nothing. wait around for a sec, and you could easily get a triple.

around level 11-13, get blue buff and at least Giant's Belt. then you can solo dragon. communicate with your jungler about wards, staying in lane so they dont suspect you're there, and all that jazz. Get a pink ward so you can kill their wards around dragon.

Late game: this is when you get aggresive. Flash in, E, Zhonya's Hourglass active. then spam til you die. AFTER you die, ult. make sure you do within 3 seconds after you die, or else you won't be allowed to cast it in spirit form. Use your Ult to initiate (communicate with the tank), or to help your team turret dive and live. Claim the jungle as yours.

NOTE: I apologize that this isn't as in depth as it was when I first posted it, Mobafire glitched when I saved an edit, and deleted this entire section. I will (hopefully) update it soon, and give you a much better explination of how to play Karthus

Pros:
Easy to farm with
Fun ult
does amazing damage
can solo jungle creeps easily
secures kills your team would otherwise not get.
Death Defied gives you a guaranteed 7 seconds to do damage
Dancing on a dead Miss Fortune or Morgana body is ROFL worthy

Cons:
always focused first (which is fine, cuz of Death Defied. just so annoying >.> )
easily countered.
soft if you dont build tanky
easily countered.
Requiem is a major KS temptation. just dont do it.
easily countered.
low mobility.
easily countered.

Hexdrinker. most people forget about it, but if they grab it, goodbye Requiem.

Soraka. If she is chosen before you choose Karthus choose someone else. If they choose her to counter you, good luck. you have to have awesome team communication, and amazing timing with your R to even hope for a kill with it. She is the antithesis of Karthus. that *****.

Heal. noob heal is super annoying. can block your ult kind of often. fortunately the Cool Down is longer than Requiem.

shields. Riven, Morgana, Lux, Orianna etc. wait til you see them use it, and ult about a second or two after they pop their shield. it should wear away before your channel ends, and still be on CD. timing is hard, practice often.

pretty much anyone with a decent heal or shield will be hard to beat. its all in timing. thats how you can tell a noob Karthus from a pro Karthus.

Summary: Work with your team. It's better that way. Don't kill steal. (ive said that like 5 times. get the point?)

conclusion: let me know what you think about the guide. I will update it when i have more time. constructive criticism is appreciated. I hope you enjoyed my take on Karthus.