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 adapt to his mechanics or 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 are 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 their dashes, then dodge a lot of his Q's, using their high move speed.
Usually he serves as empowerment to the team, not as counter to someone.

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

PROS

++Fast jungle clear. Allows quicker movemend around map for earlier ganks or jungle steals.

++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. When assisted by tanky CC-rich ally, Karthus can stay outside of enemy range and freely melt enemy HP.

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. Allows aggressive plays and tanking for other team members, and even dying inside of enemy team for ever greater zoning/dmg output from newly gained position.

++Gamechanging ult vs squishy comps, if used early.

CONS

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

--Immobile and lacks hard CC. Makes him vulnerable to 1v1 and focused attacks, including dive. Often he is target n1.

--Cannot be oppressive vs almost any jg opponent. Which allows them to outscale for free or simply snowball their team early.

--Kinda mana-hungry

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 and Q.

When Karthus jungle is good:

++When allied team can survive early and have no scaling hard counters in late game.

++Allied team have tanks with CC. They reduce enemy HP restoration from dmg dealt, and allow Karthus to attack from outside of enemy reach.

++Enemy team is squishy and cannot quickly restore HP by lifesteal/ omnivamp / healer. Makes Requiem more impactful.


When bad :

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

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

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

--Enemy JG is hyperscaler or/and 1v5 champ and want free farm undisturbed Gwen Jax Master Yi and half of the roster...

PREEMPTIVE STRIKE

PERIMETER




THE MOVES

In jungle we have 3 dueling situations for Karthus:

1.He encounters visible enemy at safe range (~0.8*Q max range). That Eneme have no strong gapcloser. From here: W> Q+move> Q+move...Q, maybe E . Ult if needed to secure kill. Optional: If they have short area-targeted dash, do not spend Wall early, allow them to waste their dash first.

2.He got into enemy dash range. Some champs can reach Karthus with dash, but cannot maintain their melee range. Like Irelia or Diana with missed "dash reset debuff spell" and w/o Stridebreaker or something. Use wall and gain distance. Often this will not save u from such champs , but definitely will take their time and HP.

**Avoid using wall first if u're in their dash range and they have it ready

3.He encounters more mobile champ with damage like Kassadin or Hecarim with that new Phase Rush, or both. He dies.


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 above anything else.

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

**Sometimes it is better to not secure single kill with Ult. Rather, keep it for big teamfight before object.



**Always start from blue buff ( or enemy Raptors, and then own blue buff) 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.



**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.

++Karthus is not very blindable champ. Sometimes he can be directly countered by jungle opponent. Or cannot neutralize enemy scaling jungler or laner, due to not always strong 1v1 or gank potential. Sometimes team shows lack of teamplay, and he is not very strong duelist.

He likes teamplay and allies with reliable CC, which enables his long range damage,and counters enemy dive. Tanky ally like Leona Nautilus can lock enemy in place and mitigate their damage, reducing their HP restoration from dmg dealt.

Default game plan is: powerfarm with occasional ganks and objects, scale for team fights, avoid engaging in duels vs diffucult opponents.

++ Rylai's Crystal Scepter is core item for most builds.

++Get at least 40 Ability Haste for more reliable Qs

++Early ults in mid-late game create significant advantage vs squishy champs. Item effects on affected champs can make allied follow-up easier.

++Non-centered Qs allow to force enemy movement in direction( s) where they are less covered by Q.