Hi everyone! I've been playing this game for a few years now and been maiming the junglier role for about a year. I'm currently in gold I on the NA server, hopping to get to plat within a week or two. I'm currently making the guide, I know its not nearly close to perfect yet. If you guys wish to contribute to making this guide even better please leave a comment with some changes you'd suggest, i'm open to discussions. If you wish to just have some fun in game feel free to add me on the NA server, username: Big Boss Lux.

Many of you might wonder why people would play Karthus jungle. With the huge Kha'Zix nerd that just came out with patch 4.9 his main counter in the jungle won't be played as much. With his e upgraded, Kha'Zix could easily just jump on earths, burst him down and then jump out.

You guys will probably see a lot of Karthus since the visual update now that he looks AWESOME

This is my first guide so if you are to down vote, please at least leave a comment so that I may know what to modify.

Hope you guys have fun reading this guide and try it out!

Pros

+ Great clear + High damage output + Q an W grant vision + Deals damage when dead

Thanks to the AOE dog and q "crits" Karthus has a great clearing speed. He deals AOE dmg but can also have great single target burst thanks to the single target crit of his Lay Waste. NO MORE FACECHECKING! His Lay Waste and his Wall of Pain grant vision, use them to check bushes.

Cons

+ Squishy + No hard cc + Dependent on blue + Long cd on ult

Unlike most mainstream junglers Karthus is very squishy and can be bursted down easily. He does have a slow but no hard cc which can make it hard for him to peel for himself. To get a good clear you must spam skills which cost tons of mana. The cd on his Requiem is fairly long, meaning that it can easily be countered (i.e. zhonia)

• Greater Quintessence of Spell Vamp: Gives good sustain in the jungle and lets you solo drag at lvl 7.
  
• Greater Mark of Scaling Ability Power: Better late game scaling. Can be replaced by Greater Mark of Magic Penetration
  
• Greater Glyph of Cooldown Reduction: Lets you spam you skills (better clear and higher damage output)
  
• Greater Seal of Health: Replaces armor and MR seals and glyphs.

Basic boots for most APs. Ignores 15 magic resist.

Great late game scaling. Gives a lot of mana, which is a necessity on earths to be able to last through a fight. The passive once it gets upgraded can be pretty strong too, but you must be careful when using it since it can make you run oom.

Not much explanations necessary, it just gives massive damage.

Very useful if their team builds a lot of MR. Better to go with other AP items if they don't. In most cases you'll be fed enough for them to stack MR so you will end up buying it most games.

This item is just great if they have either some very bursty champs (i.e. LeBlanc) or a lot of AD. Plus, you keep dealing damage with your e while in zhonya.

Since karthus is pretty squishy this item is a must buy. The slow is very useful to chase down enemies.

If your team is horrible and you're carrying them hard, this could be a good buy. Pretty useless in 1v1 situations though so this is a situational buy. You might be better off just getting some more AP, since you deal damage when deal anyways.

This guide is not completed yet, will have a section on jungleing, team fighting, different match ups and things to watch out for and much more. Please do not down vote before you actually try this out and the guide is finished.

All in all, Karthus is probably one of the top tier jungles atm and is extremely fun to play. If you wish to see some nice Karthus gameplay I would recommend watching NightBlue3s' stream, he's been playing a lot of him lately :D