Sup everyone! The time has come to tell people the truth... To expose what makes Karthus so busted that his enjoyers can print LP with him.
In this mini-guide I will explain Karthus' identity and provide nice builds and tricks.
For better looking text, use zoom feature. For me (win 10+ chrome), it is Ctrl+ Mouse wheel UP

He is niche champ, who mostly played by mainers, similar to Vel'Koz. Cuz often it is difficult for player to find his vibe and purpose. His Q Lay Waste high dmg output from significant range, slow from W Wall of Pain makes him strong addition to almost any properly played teamfight. However, such teamfights not always happen, and he suffers from lack of team assist.
He can be beaten in 1v1 early and late by decent number of jungle opponents, as they often can ignore slow effect of his Wall by mobilities or sidestep, then dodge a lot of his Q's, using their high move speed.

I treat him as Zoning Team-reliant High-DPS champ. AP carry with extra range. Almost great champ if not his very special Q.

PROS

++Fast jungle clear.

++Strong at zoning. Spammable long range Q is big problem for squishy ranged carries and not very mobile tankier champs with large hitboxes, such as Voli, Morde.
W wall is very strong in choke points. Enemy cannot feel safe near their tower,cuz safety is not real here and the wall can screw it.
* Common mistake: placing wall too early/far, without being able to follow it with own/allied dmg/chain CC.

++Fail-deadly/cheesy main passive. Makes him useful mid-late even in some unlucky scenarios. Allows aggressive plays and tanking for other team members, and even dying inside of enemy team for ever greater zoning/dmg output from new gained position.


CONS

--Mechanically not easy at first. Main dmg source Q is not reliable spell, can be easily dodged, often requires slow from W or Rylai's Crystal Scepter or allied champ with CC.

--Immobile and lacks hard CC. Makes him vulnerable to 1v1 and focused attacks


In jungle Karthus has no mana issues, and can utilize his strong clear for powerfarm, earlier ganks and scaling for team fights. He need to be careful about invading junglers tho. He can provide decent level of assist when ganking lanes, but not always, due to not very reliable Wall CC.

It may be weak pick if ( list is not exhaustive) :

--Enemy champs are too mobile and allies cannot provide enough CC

-- Enemy jungler is active and strong early ganker, and can snowball enemy scalers out of control. Jarvan IV Warwick

--Enemy JG is scaler who becomes strong relatively early, and can counter Karthus by their skillset and/or standart build Diana Nasus

--Enemy JG is hyperscaler or/and 1v9 champ and want free farm undisturbed Gwen Jax Master Yi and half of the roster...

PREEMPTIVE STRIKE

PERIMETER




Additional stuff:

**Don't forget to move between casts to maintain the necessary distance, which should be enough for series of Qs, and outranging enemy attack/ spell range at same time. "Stop movement" key can be useful for this.

**Q, then W asap guarantees Q hit and maximizes DPS. Can be tricky on some terrains, so it can be W+Q instead. W+Q if we want precisely placed Wall first of all.

**Autoattacks and most spells have self-lock animation time and can be answered with your Q for better chance to hit

**Always start from blue buff ( or enemy Raptors) unless it is occupied by strong enemy group.

**Large Krug, Wolf, Raptor can be hit by "solo" Q. After they lost enough HP, use multitarget Q. Use E when possible if affected by Blue buff, unless it eats all mana and makes u unable to finish camp with Qs.

**Learn where Large mobs are and how to pull them with Q from max range and out of sight. Move closer to next camp between casts.

**Do not stay idle, if u're rooted, fight back with Qs, until root ends.

**When ganking, use pings near allied champs so they can see it. Do not ping too much. Two single signals with 3+ s delay should be enough to show that u comin.

**To get gud: 0.Learn how to draft.( important on non-blindable champs like Karthus) 1. Analyse ur own mistakes by using replays 2. Learn from the replayss of high-elo sweats 3. Do not take anything too serious. 4. Respect break timers and playtime limits.



Wut about Rylai's Crystal Scepter, my precioussss

This thing is CORE item unless your team provides enough CC for your Qs to hit. Utility level is insane. Give it a try. Allows much easier times against melee dashless champs. Thanks to your E-Defile. Single hit by your Q can lead to easy deadly sequence. With help of your W wall it is guaranteed vs dashless champs. Slow from Ult can be useful for teamfight if timed well.