The first time I tried to jungle karthus I found it impossible simply because I could not figure out the right runes and masteries. This guide is an attempt at a brief tutorial on the ins and outs of jungling with Karthus, as well as a few warnings and important tips. I will be posting a video on the jungle route within the next couple weeks to make the guide more explanatory.

Keep in mind jungling Karthus is not an easy feat, but the extremely effective ganks and early game kills you will get your team make it worth the while.

Pros
+Karthus provides excellent ganks, and his ult out of nowhere can be terrifying.
+Karthus is an aoe jungler, with Defile and Lay Waste he can destroy the jungle.
+When covering a lane, Karthus can farm extremely well and keep the lane pushed while harassing the enemy in lane.

Cons
-Karthus is an extremely tempermental jungler and is very dependent on his runes and masteries.
-Karthus is very difficult to jungle for inexperienced junglers, and using the wrong combos on minions can result in disaster.

Runing jungle karthus is extremely similar to runing mid karthus, with one small change. Karthus is extremely squishy in the jungle, so armor yellows will allow him to resist more of the jungle's early damage. Also, armor yellows help when ganking top and bot because the AD carry bot will do less damage, as will the tanky DPS top (assuming they have an ideal team comp).


Greater Glyph of Force
While these runes are not ideal for early game jungling, they will help Karthus carry late game. They provide the most 3x more AP than flat AP runes, so I prefer them even when jungling karthus. If it is more important to you to be strong early game, go with flat AP blues.


Greater Mark of Insight
This is the obvious choice for any mage. Karthus does not need armor reds because with the right masteries and yellow runes he is plenty tanky in the jungle. Magic pen reds allow for more magic damage output to enemy champions, and will be extremely helpful going into late game when the enemy starts to build MR.


Greater Quintessence of Potency
Another obvious choice for mages, these Quints help Karthus early game for more damage output in the jungle as well as more damage when ganking. They supplement the lack of flat AP on your blues, and provide enough to get your first couple of items.

Masteries are what makes or breaks Karthus in the jungle. Normally, a mage will want to go either 21/0/9 or 9/0/21, but in the jungle this destroys karthus. You can use normal mage masteries only if you know you can get a hard leash blue and support to prevent counter jungling. This is dangerous, however, and will also reduce the amount of ganks you are capable of putting out. Therefore, either 9/21/0 or 0/21/9 is the best way to go for a balanced jungler. The choice between the two is up to user preference.

There are a few core items you will need as karthus when jungling.


Tear of the Goddess is important to keep up your mana pool early game after blue buff wears off, especially so you can have enough mana to gank, and regen it on the way back to the jungle. However, if you constantly have blue buff early game Tear of the Goddess may be unecessary, and you should switch it out for some early AP items, such as blasting wand.



Hextech Revolver is a must - have if you do not buy many health pots after your first jungle path. This combined with Tear will give you more than enough sustain in the jungle and out of it.



Sorcerer's shoes I prefer to Merc Treads simply because jungle karthus does not have as much damage output early game as would be desired, and 20 extra magic penetration helps to solve this.


Rabadon's Deathcap. A must have on every karthus.


Rod of Ages is a very good item for early and late game tankiness and sustain, and balances health with mana and AP.


Archangel's is an important item for karthus when going into late game, for the extra AP and mana. Deathcap five Archangels is the best build ever.


This item is optional, but is very good for teamfights if you are fed and being targeted.


Void Staff is optional and circumstantial. Get this only if the enemy is building a lot of MR.


Abyssal Scepter is another good item for enemies with MR, and is really good if you are in the middle of teamfights doing tons of damage.


Very important for AP and tankiness, and very desirable because it now makes your Q slow. Combined with Wall of Pain, the enemy (albiet Singed) will never be able to get away.

Lay Waste

This skill is very important to max early in the jungle. It allows for large amounts of damage when fighting a single target, as well as very good aoe damage when using it against three or more minions. This is also important to max for ganks, as this is your main damage output.

Wall of Pain

This skill is important to get only one point in early on, the only reason being for ganks. Nothing much really needs to be said about this ability.

Defile

This ability will help you a lot, especially early game, when jungling. However, it is important to be careful about using it because it will drain your mana like nothing else. Ideally, use it on blue, red, wraiths, and wolves, when you have enough mana. Late game with blue it will be spammable in the jungle, and so take advantage of this.

Requiem

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Global massive damage. Simple as that. Use it when the lanes need to secure a kill, or after ganking for most of the enemy's health. It is also a good initiation for a teamfight, especially when trying to force baron. Awesome for ks-ing as well.

My Preferred Spells

Smite

This Spell is necessary for jungle karthus, because he will not have enough damage to kill blue buff/red buff and other jungle camps without it. It speeds up the jungle and can be used as a last resort if you would otherwise die in the jungle.


Flash

This summoner spell can be very good on karthus for early game ganks, and it is a good distance closer during teamfights, or a quick escape. Depending on how insane you are, flash->Wall->Defile->Lay Waste up the butt right into the middle of the enemy team is an excellent way to win a teamfight or just have some crazy fun.


Ghost

Awesome summoner spell for early game ganks, chasing down people in a teamfight, escaping. More appealing since the flash nerf. Choose between this and other summoner spells based on your own preference.


Teleport

Great summoner's for split pushing lanes, and can be helpful if your team needs you or you want to clear a massive minion wave. (As karthus is the best champion at clearing waves quickly in the game).


Ignite

Good for one - on - one fighting, especially if you want to secure a kill with ignite -> ultimate. However, this is more for using in - lane and there are summoners that can be used better on jungle karthus.


Clarity

This spell can be used for inexperienced jungle karthus', as your mana pool will be drained like a boss early game using defile in the jungle. However, I would not recommend it, and would prefer Flash, Ghost, or Teleport.

You always want to start at Blue with Karthus, getting a leash if you can, but this is not necessary. Then proceed to wolves and use your Lay Waste to pull them to you, then Defile and spam Q until they are dead. Walk over to Wraiths, then Lay Waste and Defile all of them. Then pull Golems with your Lay Waste, and continue to Q them (save defile for now). Walk over to red, and use Q and defile on all of the minions, including red buff. Smite red buff, and then go back, buying Amplifying Tome or Boots of Speed with Health pots.

Play Video

Get blue. Toggle your defile. spam your Lay Waste. I don't really need to say any more.

Jungle Karthus is not one of the easiest junglers to master, and will take some time experimenting with items to buy as well as styles of jungling to use. Try it out a few times first in a custom game, ensuring you can get the entire jungle cleared (including red buff) without dying and without a leash.