Build Guide by P.DiddyXD
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Not Updated For Current Season
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Karthus is by far one of the coolest characters and has not only the most 'rage-quiting' ult but is also really fun to play! This guide looks at karthus's weaknesses and fixes them via correct item choice and gameplay. Unlike most guides, i do not use rod of ages for karthus simply because it takes ages to get the added bonuses when in fact you want the power right now! Using this build, ive managed to get on average 15/2/10 with karthus with a best of 28/1/22 (having gotten 3 pentakills with karthus in real matches).
MASTERIES & SPELLS:
Standard 9/0/21 for ap mage. I find teleport and flash the most useful since you can hold mid (yes karthus should alwasy get mid) quite easily and shop at the same time with teleport. And flash is a must since karthus is very squishy and needs to get out of melee range very quickly! The other alternatives commonly seen are clarity and ignite; you dont need clarity if you last-hits minions for mana regen and if you build tear of the goddess (TOG) you will have large amounts of mana. For beginners, you must learn not to needlessly spam your wall of pain or defile early game (which costs a fair bit), and instead use lay waste to harass and last-hit minions. As for ignite, since you have tons of ap runes and you are stacking lots of ap early, you will always get your kills - even if you die you can throw down some lay wastes and finish with requiem (ur frickin awesome ult!) to kill them, so really death is not a problem for karthus and since he does not need the slight damage from ignite, its really a waste.
While it is not essential to get all the skills early on, i find it useful to prevent early ganking through at least 1 point in wall of pain and also 1 point of defile (which scares most players away due to high dps). So basically max out lay waste (an extremely cheap and powerful spell if used on a single target) and of course your uber ult requiem (at levels 6/11/16).
The reds are magic penetration (definately a must), whilst the others are ap/level (this is better than flat ap since the benefits are greater by lvl 10, and since you are mid you will reach it fast). AP runes make karthus god! No amount of health runes will help his squishyness, you just need to learn to play with 'safely' by kiting and annoying the **** outta people with ur wall of pain + lay waste as harass (and of course punish those idiots on low health using ur ult!!).
Ok so you must be wondering 'OMG hes a noob cos he doesnt get rod of ages?', so here are the reasons for my item choices:
1) getting majai's is risky; this is true if you dont play smart or the opponent team ganks too much, however i highly recommend getting it since karthus' ult can not only nuke ppl from range to get kills, but it counts as assists too! Also, the best thing about karthus is that even if you die (and become the ghost via his passive 'death defied') you can get kills using ur abilities and so still maintain ur majai stacks!
2) karthus is so squishy that people will stun/slow him and towerdive the **** outta him; thus, getting zhonyas to negate tower-divers and then turning the tables by using wall of pain to slow them + lay waste to hurt them will easily counter their futile attempts of diving him.
3) karthus has early game mana issues; getting TOG is a cheap way of granting him unlimited mana for mid-end game (if you play smart and dont waste ur mana unnecessarily, the blue buff is not even needed). Plus, only upgrade to archangels later on since its major ap boost is based on your maximum mana, which is usually only significant towards endgame so its better to invest this ap money into other more useful items in the short-term.
4) karthus generally has very low health; rylai's fixes this easily, plus provides decent ap with a slowing effect to all your damage spells! Whats not to like?
5) once ppl see karthus, they will stack banshees or magic resist (MR) like force of nature; this is where things get annoying, because you think that ur ult can finish them when all of sudden they have a 'shield' or hav enough MR to survive the blast. This will usually happen by mid-late game, as such, a void staff is a must to counter their MR and make your spells (particularly ur nuke) hit harder! As for the gay banshees veil, the trick is not to initiate with ur ult anymore (yes karthus does should not ks the team, but rather assist the team by reducing all opponents health and scaring them), so you should ideally wait til their 'shield' is down. This can be particularly tricky for characters such as morgana/sivir/shen/vlad who have skills that block your ult.
6) getting another archangels staff late-game; If the game manages to last this long, you will have a massive mana pool and so another staff is a cheap and effective way of getting lots of ap (although if ur loaded and dont have 4k mana, then another zhonyas is always good). Here i have suggested getting a void staff for the extra magic penetration, however if your opponents do not have MR, then by all means you should own them even more by getting another archangels staff instead.
TIPS & TRICKS:
i) 'the chase'; if an opponent is on half health or are simply afraid of u (as they should be!) cast wall of pain behind them and they will always run into it, becoming slowed. Then aim lay waste infront of them as they flee and it will always blow up in their face, drastically reducing their health. Continue chasing until they die or if they reach their tower, you would have them on very low heatlh (less than 400 is advisable) and then you should initiate ur ult immediately (due to cast time and since they will try to recall). This combo always works on non-healing non-tank champs, although do note that some champs hav higher MR or 'shield' abilities that prevent you from finishing with your ult so its best to wait til they have really low health or hav their 'shield' on cooldown.
ii) 'the great escape'; if a melee champ rushes towards you then you must immediately cast wall of pain inbetween you and the approaching champ, then run or flash away. Too often i see ppl cast wall of pain much too late to be of any use. Also, as you flee, you should learn to quickly cast lay waste behind you so that they get damaged if they pursue the chase (this takes some time to practice and learn correctly without slowing you down much).
iii) 'fishing'; if you are on low health and are near your tower (with zhonyas ready), kite your opponent towards your tower and wait til they try to dive you, then activate defile (your uber dps magic 'circle of death') and quickly cast zhonyas. Not only with this surprise them, but they also gain tower agro from trying to dive you and you can severly damage them with defile. Usually they are forced to retreat or recall, if you manage to do heaps of damage then by all means ult the **** outta them :)
iv) 'i see you'(sauron voice of course lol); a lot of people think that karthus' wall of pain is quite useless, however this is wrong! It is extremely useful for checking bushes and preventing ganks, not only that but since it increases in size and duration, you can use it to gain massive line of sight of your or your opponent's jungle. This can be great for setting up ganks or countering opponent ganks! You can also easily check the baron and dragon safely by standing on the other side of the cave and casting your wall down for line of sight - this can lead to some very interesting ganks!
v) 'power from beyond the grave'; if there is a massive team gank, and you know your opponents are squishees or do not have MR, it is always best to go along with your team into the 5v5; this is because you can once again activate defile for some massive aoe damage whilst throwing walls behind them to keep them within the aoe. If they focus you, as they always will, then activate zhonyas. If you die and become the karthus ghost , then keep spamming your lay waste to get kills or assists and time your ult carefully to get the pentakill!!! Ive done this numerous times and it pretty much wins the game since your allies can just rush their inhibitor. Alternatively, if you dont wish to kamakazi, then you can always play the standard 'roa' karthus move by standing far back and nuking them, however this playstyle is far too passive for karthus' amazing ap ratios.
To solve mana problems, make TOG.
To solve tower-divers, rush zhonyas.
To get bonus health, make rylai's.
To become an op god, stack your majais quickly, finish your archangel staff and own with void staff for added magic penetration.
Play smart and dont be scared of death for it is only the beginning.... to a pentakill! :)
GL HF ALL!!