Hello my name is Mampex but you may know me better under the name "Gaufre99". I play League of Legends since season 2 and I got to Diamond 5 (not the best but hey I am happy!) By playing pretty much only karthus from platinum 5 to D5.
Even though i do not have as many games as karthus as I do with, say Rumble or Fiddlesticks, I have played him a fair amount, so I thought I would make a guide for my friends.

Karthus is a Mage, an AP carry who is not seen much anymore but everyone has heard of him as a "braindead" or "noob" champion because of his ultimate.

I'll try to give you tips on him and eventually I hope to improve at Karthus myself!

Let's starts with Karthus' strengths and weaknesses:

Pros:

-Very easy to farm with.
-One of the best late game champions, every item you get is a power spike.
-Fantastic team fight presence.
-Very fun to play :)
-Ridiculous damage, you will often be top damage dealt (which is all that matters by the way)
-Global ult means you can help your whole team as soon as you're level 6
-Great passive, you can die in a team fight and still be useful

Cons:

-Really immobile, so you have no escape and might have a hard time catching up to people with dashes or blink.
-Horrible mana problems
-While he is not THAT terrible early game, Karthus needs some levels before his Lay waste deals enough damage to 1v1 a lot of champions
-Wall is awful at rank one and needs to be maxed last
-Very long cooldown on ultimate early game
-Can be camped and rendered useless
-Need to be good at hitting bonbecs
-Not a lot of cc (only slows)

After all, karthus has a lot of problems, but I'd say his pro's outshine his con's by a mile if you know what you're doing.

Next up I am going to explain Karthus' spells.

His passive, Death Defied, allows him to still cast spells for 7 seconds, but he cannot move, auto attack, or use summoner spells during this time.


This passive is probably one of the best in the game. It allows karthus to go full DPS, and even if he dies, he will remain relevant in a team fight. Your Defile will be cast automatically if you die and your spells cost 0 mana so do not worry about that. However, you cannot cast your Requiem if less than 3 seconds are left on your passive so you have to chose the right time to use it.

His Q, Lay waste (the bonbon as I like to call it) Creates a delayed blast (delayed by 0.5 seconds i believe) on the target location That deals damage to all enemy hit. If you only hit one enemy, the damage dealt is double (including the ap ratio from 0.3 to 0.6)

Your main Skill, 1 second cooldown and it deals a lot of damage, since your auto attacks are horrible and low ranged, use it to farm aswell. You also get mana back while last hitting as soon as you have a point in Defile.
You need to pretty much predict where the enemy is going to go, dash, try to juke or run to.
For example, if nidalee lands her spear on you, that probably means she will try to use her cougar jump on you, so put Lay Waste to where she is going to jump to instead of her actual position.
If you are chasing a champion with a dash, say lee sin, and you think he is going to ward-dash over the wall, use your q to the point you think he is going to dash to instead of where he is right now.
The same goes for a lot of champions. It's also obviously up to luck since your opponent might play it differently, but eventually you'll do it as if it was basic knowledge.
When trading 1v1, try to isolate your opponent from his minion wave so he takes double damage.
This spell procs rylai's and deathfire touch in two different ways:
If you hit a single enemy, it will count as if you used a single target spell (4 second deathfire touch, 40% 1.5 second slow from rylai)
However, if you hit more than one enemy, you will get the aoe effect (2 second deathfire touch, 40% 1 second slow rylai)

His W, Wall of pain, creates a wall that slows and reduces the magic resistance of opponents that pass through it for 5 seconds

Pretty interesting spell. The wall is in no way a one point wonder, yet you still have to keep it rank one until level 14. It costs 100 mana, which is enormous early game (like 4 Qs) and slows by 40%, unfortunately this slow decays over the duration. You need to place the wall either to block off an enemy's path, or directly on top of him to proc the slow and MR debuff immediately.
Thankfully, not all is bad for this spell, as when you actually put points into it, it grows in size and slow amount which gets to a ridiculous 1200 units size and 80% to 40% slow over the duration!
Obviously with rylai, this makes karthus great at chasing and landing lots of bonbecs on the enemy team.

His E, Defile, passively regenerates mana every time you kill a unit (this scales with the rank of the ability)
When activated, it deals magic damage in a zone around karthus.

This spell is not very good until late game, and has a huge problem, the damage rate on it is horrible (once every second). This means that enemy can avoid taking damage from it sometimes if they get out at the right moment which kinda sucks. Anyway, early game this deals probably less damage than an auto attack, but it can help you last hit and deal some damage to melee champions, don't underestimate it.
Don't underestimate the mana cost aswell, as it ramps up very quickly if you start using your Qs alongside it. When you get a few ranks in it though, it starts to really deal significant damage. Anyway The mana regeneration on it is really nice, it means you can farm with Lay waste with very little mana loss and if you kill something with an auto attack you get a lot of mana back. This spell is also very scary in team fights, it's almost a mini fiddlesticks ult when you're full build, and it scares melee champions away from you.

His R is Requiem. Karthus Channels for 3 seconds before dealing magic damage to every champion alive, regardless of distance.

This is probably karthus' Signature Spell I'd Say. Requiem is a very scary ultimate, and the longer the game goes, the more damage it will deal.
Because it is guaranteed damage on 5 people (unless they have zhonya's, a spell shield or something to avoid it entirely), this means you will deal ridiculous damage overall in a team fight with this spell alone.
However, this spell's cooldown is extremely high, especially at rank one. Which is why you should try to not waste it. try to watch for an opportunity to ult bot lane at level 6 for an assisst or a kill (don't use it just to last hit champions, but also don't use it too early as your opponent might flee when they see your ult)
In team fights, you should use it mostly when you are dead, since you will probably get either killed or CC'd when channeling and in passive you cannot be stopped.
Try not to team fight when your ult is down, unless you are at an advantage, as even if you mess up, your ult might just help win it. It's very important. Otherwise tell your team "My ult is up in X".
Watch for enemies CD's, for example, if you really need to kill sivir, focus her with lay waste until she is forced to use spell shield for it, then use your ultimate.
The same goes for zhonya, fizz's E, Vlad's W...
Also, mid game, watch for enemy items, sometimes they seem low enough for your ult to kill, but they might carry hexdrinker, or items that give a lot of MR like spirit visage.
Late game try not to ult for one person, unless your team needs that person out of the fight before you can even face your opponents.

Some combos:

W-Q:
Quite self explanatory, just use your w on someone, then it is way harder to miss your Lay waste, and it reduces their MR.

Flash-Q:
If you flash and use Q, assuming the enemy has no dash or escape and they are low enough to die, it might just surprise them enough that they'd die before being able to dodge. Don't Q too late after flashing obviously, as this is all about the element of surprise.

Flash-E:
If the enemy is once again super low and you know they would die from just one proc of your Defile, Flash and use E immediately. Your E deals damage instantly so they will probably die. ;)

Q-R:
Best done in passive. Spam Q until you cast it, then spam your R key and you will ult at the same time your Q hits. This allows you to get perhaps one more Q in before you are not able to cast your ult in passive or they get out of range. It seems complicated but is actually really intuitive. I am not good enough at english to explain it properly though i guess.


That's pretty much it since karthus is not a combo caster but rather a champion with only one spammable spell, one AOE with no cooldown and two long cooldown spells.

In the early game, cover your jungle so you do not get invaded on. But be careful.
Lay waste gives vision so don't hesitate to use it to scout brushes once or twice.

Then, start farming. Do not push the lane, unless you are versus a low pressure jungler and a mid laner that will have lots of problems farming under turret, but usually, I just like to get the lane to push towards me.

At level 3 if your opponent is low ranged you can perhaps bully him with your isolated Q, but do not take too much damage back.

Remember that your main goal is to scale and farm as you will probably outscale your opponent, and if not, be as useful as him in team fights.

I'd say mid game starts at level 8/9.
By this point you perhaps have your Rod of Ages and maybe even your sorcerer's shoes, which means you deal a lot of damage. If you have exhaust up, and assuming you are even, you probably can start trading 1v1.

Focus on farming still, Roam only if you know you are not wasting your time, but help for objectives such as dragon and even herald if needed (don't take it though it sucks on karthus)
Farm Wraiths if your jungler doesn't give you blue by the way

30+minutes, at this point, you are really strong.

You will probably have void staff thus dealing a lot of damage.
Aim to team fight when your ult is up.
In team fights, active defile, wall them, and spam Q, go in the middle of them and deal as much damage as you can while getting closer to them, then you will probably die. Q a couple time and R, that's it really.
Remember that you are fantastic at taking baron so help your team if they want to do it. That's it really.
Remember to focus their mvp most of the time, you don't always want to stay in the back and peel.

That's pretty much it, if you drag it to late game, you can win a team fight by yourself.

Well that's pretty much it, was just a guide I wanted to make for some friends of mine!
I hope you will enjoy playing karthus with this guide and that's it.

Good bye!