Magic penetration, there isn't other choice for a AP caster :P
I take HP/level because I usually buy , so I don't need mana regen yellows. +180HP at level 18 is a free Ruby Crystal. You will be a little bit beefier, which is awesome.
Other viable choices: MP5/level (if you really insist), Flat Armor (if you are fighting Urgot or Jax).
AP/level is a personal choice. I like the extra AP so I can be more deadly at late game, but there are other great choices.
Other viable choices: Flat MR, MR per level, Flat CDR, CDR per level, Magic Penetration, Flat AP.
I only buy my first item with AP after I got my Tear, Catalyst and boots (unless I started with Doran Ring), so I take this Quints to have some extra AP at level 1. +15 AP makes a difference, trust me!
Other vialbe choices: AP per level, Movement Speed, Flat HP, Flat CDR, CDR per level, Magic penetration.
Seriously, rune choices will change according to your playstyle. The ones I listed are the most common.
Flash is a must on Karthus. You are very squishy, you have no escape mechanism, and you will be focused in teamfights, and sometimes, you need to flash and toggle E to rape the enemies (example: Amumu uses bandage toss and ultimate, what do you do? FLASH AND PRESS E + QQQQQQQQ, you will deal a ****ton of damage, and the enemies will be too damaged to fight back)
For the other slot, I usually take , for the extra MS for escaping/chasing, but there are other good choices:
Exhaust is awesome to shut down carries and damage them while they are slowed. Exhaust + = lol.
True damage, healing reduction, all good, I don't usually pick it becase I'm used to double escape summoners, but it's great.
I'll talk about his skillset more in depth during the early-mid-late game chapters, because it is very peculiar.
Passive: Death Defied
Upon dying, Karthus enters a spirit form allowing him to continue casting spells while dead for 7 seconds.
Great passive, you deal a ****ton of damage, so the enemies tend to focus you on teamfights, the problem is, when you die, you can still be dealing damage.
Make sure to have E toggled if you die, your enemies will be very damaged if they stand fighting on your corpse, which gives a zone advantage for your team.
You can use your ultimate in the first seconds of zombie form.
Q: Lay Waste
Creates a delayed blast at Karthus' cursor position. After 0.5 seconds, deals 40 / 60 / 80 / 100 / 120 (+30% of ability power) magic damage to each nearby enemy, this deals double damage if it hits only a single unit.
Cost 20 / 28 / 36 / 44 / 52mana
Oh ye, 1 second CD AoE nuke. Deals double damage (0.6 AP ratio) if it hits one unit only.
You can use this for farming, checking bushes (gives you vision) and basicly rape your enemies. Don't be afraid of spamming it, the mana cost is short, and with my build, you will never run out of mana.
Lay Waste gives vision of what's in the bush. Don't facecheck pl0x.
W: Wall of Pain
Creates a 800 / 900 / 1000 / 1100 / 1200 distance wide wall through target point. Reduces enemy armor and magic resistance by 15 / 20 / 25 / 30 / 35 and reduces movement speed by up to 40 / 50 / 60 / 70 / 80%; debuff lasts 5 seconds. The wall lasts 7 seconds.
5 second slow with magic resistance debuff, your only form of CC.
If an enemy tries to attack you, make sure you use this right on him, fill his face with and he will start running away (unless he is a tank, in that case, just use the wall and run).
I forgot to mention that Wall of Pain also grants vision (which is also something pretty big to forget, thanks Rosuto), and the area covered is actually pretty good.
I have vision of the bush and a small area surround it.
When you place the wall vertically, you still have vision of the whole bush.
As you can see in the minimap, it covers a large area.
Toggle Off: When Karthus kills a unit, he restores 20 / 27 / 34 / 41 / 48 mana.
Toggle On: Drains 30 / 42 / 54 / 66 / 78 Mana to deal 30 / 50 / 70 / 90 / 110 (+25% of ability power) damage to nearby enemies each second.
Great AoE damage over time and it refunds mana when you kill an enemy (doesn't need to be toggled on to restore the mana, which means you can recover your mana in laning phase very easily).
Just keep this on during teamfights. If you are CC'd, the ability doesn't go off, you are just unable to toggle it off during the disable duration, which means you will be dealing great damage even when you are CC'd. Cool.
After channeling for 3 seconds, Karthus deals 250 / 400 / 550 (+60% of ability power) magic damage to all enemy champions (regardless of distance).
Cooldown 180 / 150 / 120 seconds
Cost 200 / 300 / 400 mana
Ah... Requiem. The only global nuke in this game.
Requiem > Lay Waste > Defile > Wall of Pain
This is what I do in most of my games. I max first, for more damage and easier farming, then I max for maximum presence on teamfights, taking a point in at level 4 for the slow and MR reduction, and maxing is last. I level up at levels 6-11-16 (well, derp).
If your team doesn't have enough CC, it might be a better idea to max after your level 3 Defile. It's up to you though.
Karthus is a pure AP Caster, therefore, he benefits from stats such as:
I start my games with a Sapphire Crystal and 2 hp pots, for more Q spamming and health regen.
Starting with Boots of Speed (and 3 hp pots) might be a better option if you are laning against a good harasser or if you are going for a skillshot dodging contest:
If you don't feel confortable with starting with 4hp bars, you can either chose flat HP quints (like I suggested in the runes section), or you can start with a Doran's Ring . I don't recommend it though because you can't buy any HP potions (which is bad), and Catalyst gives you enough HP for the early - mid game... but I suppose you can skip Catalyst and buy another Dorans Ring.
At the first trip back, you want to buy:
(buy as many as you want)
This is hella expensive, most of the times you won't have enough for the full , but I recommend to go back to store again whenever you can buy it, because it's an awesome item.
gives you a giant mana pool, and it's easy to stack it because of your low CD .
even more mana, a good amount of HP and an awesome passive. If you can't buy this item at the first trip, just buy the recipe if you can.
deeeeerp. Kinda obvious.
Buy wards to protect yourself from nasty gankers, gogo map awareness. HP pots are a cheap way to recover hp.
After first trip back, you should buy:
Imo, buying Mercury Threads is not worth it, because if you are CC'd you die, and when you die you can still deal full damage without being CC'd, so whatever.
is a must on any Caster, ****load of AP.
This finishes your core build. Yes, there is only 1 AP item in the core build, but this makes your early game much easier, and you will be a beast at mid-late game, when the teamfights start happening.
So, what should I buy next?
You have .
Good offensive items:
is an awesome item, most carries buy a Banshees Veil, and this is a great counter for that. Magic penetration is allways good.
gives you a ****load of AP because you stacked your Tear of the Goddess and your Catalyst.
gives you some CDR and a good amount of AP. Decent item, but I don't like it because it reminds me of Morello.
situational item. Small amount of CDR and AP, only worth buying when the enemy carries are stacking alot of HP and no MR (rare).
awesome passive and it makes you beefy. Great item, I build it in 99% of my games (other 1% the games end before I can buy it).
**** yeah, the active + Defile in the middle of teamfights = rape.
a good amout of ability power + Magic Resist + an awesome debuff aura (You can make the enemies MR drop below 0 with MR reduction). What else do you want? ~.~
if you INSIST in having some tenacity, you can buy this item, but I don't like it, because the amount of AP it gives is... very tiny?
You can also buy if you are constatly being surpressed by a Malzahar or Warwick. It won't save you from death if you get caught out of position, but they will think twice before using their ults on someone with a and a Banshees Veill QSS at teamfights.
Your late game build should be somewhat similar to these:
VS. heavy AP:
VS. heavy AD:
RAPE EVERYTHING ON YOUR WAY.
Don't forget to buy and if you can .
THE LANING PHASE! Woop, QQQQQQQQ
Karthus is a strong laner & farmer, you should allways take solo mid or solo top. Your damage output with Q is average if you hit more than 1 enemy and LOLWTFOMG if you hit 1 single enemy, which means, if you see the enemy champion in a position where you can hit him only, do it.
Learn to last hit minions easily by positioning your lay waste in a way it only hits the minion you want to kill.
You need to know your Q's range and AoE. To see the AoE cyrcle and the ability's range, you can click the ability icon with your mouse ^_^
It takes a while to master this, but it's totally rewarding, because after you memorize it's range, you can just harass your enemies super effectively.
As you see in this picture, I'm about to harass this high elo Sivir player, while tanking the cannon minions damage.
Once you hit level 6, the enemy team will start being more careful because of your global ultimate. This gives your team an enormous advantage.
Ask your teammates to warn you when you can kill an enemy with your ultimate, because you can't be watching their lanes 24/7.
Anyway, don't waste your ultimate in champions with spellblock abilities (ex: Sivir and Nocturne), because it won't do ****, and you might end up losing some kills because your ultimate is on Cooldown when you need it :(
Keep in mind that it's cooldown is huge.
SUP DRAGON, PEW PEW, QQQ
The fun begins here.
Continue farming like a boss, but try not to get yourself too low, because a dragon fight may occur, and you don't want to be shopping/super low on health when it happens, because it's a huge disadvantage for your team. Ask your jungler if you can take blue buff, and ask for his help to do this, you don't want to lose some precious HP to a neutral monster.
This stage is decided by the number of dragon kills & turrets down. Karthus is a good pusher, because he can kill entire waves in seconds when he toggles .
Q + E = bai bai minion wave.
Even though you don't have a autoattack steroid, you can take the tower down quickly if you manage to get a big creep wave on your side.
About dragon.. just make sure you have it warded. You can kill dragon with your jungler and bottom lane quite easily (W+Q+E all the time = dead dragon in no time).
If you see the enemies are coming to dragon, ping like a madman and make sure your entire team is coming to it (top may join the fight a little later).
Just use W on them, poke with Q and make sure they don't take dragon OR kill atleast 3-4 of them.
Karthus ultimate can take 1/3-1/4 of the squishies hp at late game, if you farmed decently (200-250 CS).
His Q deals a good amount of damage on a super low CD, and Defile deals enough damage to keep the meelee champions scared of getting close to you.
Allways, ALLWAYS follow your teammates. Don't be around alone, because you don't have any escape mechanism other than your summoners.
Ask your team mates to help you (follow you and protect) taking the blue buff, because you love the CDR. Hm.. yeah... dat CDR is so sexy.
As I said in my Ezreal guide, don't go farm bottom when the enemy team is all mia, because you may:
A) Get ganked and die.
B) Give away a free baron.
C) A and B.
Fighting for baron
Ahyeye, the big worm, it's amazing how it changes the tides of games. Baron fights can result in a secure win or an epic comeback, reason why they are so importat. dat buff is so gud.
If you are doing Baron with your team, use wall when the enemy team comes near you, so it's easier to get outside the baron cave and rape the enemies. If you are on the team who is going to gank at baron, just make sure you use W on the small entrance and poke them with Q. Eventually, they will get out, if they are dumb enough to keep baron'ing, just ask to your tank to initiate on them, because they are taking baron's damage.
Karthus is an awesome teamfighter. He deals a ****ton of damage even after dead, eheh, awesome.
If you know a teamfight is coming, make sure you aren't out of mana (may happen at midgame), and stay behind your tanks.
You should never try to initiate by yourself, wait for your tank (or the enemy team's) to start the fight, and then GO CRAZY. If you want to maximize your damage, you can use flash and toggle to hit as many champions as you can, forcing the enemy team to either focus you and stand in your AoE for too long, and then watch you continuing dealing damage while dead, or spread and get caught of the position (NOTE: this tactic isn't safe, do this if you are sure your team mates are good enough to rape the enemies while you do this, otherwise, you just died for nothing).
If you don't trust your team mates to do this, you can just stay behind, spam Q Q Q Q, try to use W to debuff the enemies MR, toggle E if an enemy comes near you, and press R if the enemies have their Banshees popped and are low on hp.
Oh, and for the ****s sake, don't use your ultimate in the middle of teamfights. If you get silenced/stunned/whatever, your ultimate doesn't work and its cooldown is not refreshed.
Weew, I hope you liked this guide. Karthus and Ezreal are 2 of my 5 favorite champions (other 3 are Irelia, TF and Malzahar), so I really wanted this guide to be... decent at least.
All the Karthus guides on this site are... bad, but I hope this one is good :3
"Their pain is my pleasure >:)"
Be smart, rape hard and make them rage!