As you can cleary see, I always wanted to play with some kind of INSTANT-PENTAKILL-Karthus. The Pentakill-Skin would be recommended to pro-players or to godly players like me.
If you closely follow my well-written guide, you will achieve glorious stats (e.g. ∞-0-0). I will add further proof when I'm ready to do this.

But why should anyone choose Karthus as his Champion? Let me show you some delicious features, which uniquely belong to Karthus:

Ultimate Karthus is the only Champion, who can cast such powerful magic without even dying of illnesses like, i dont know, eye cancer or something similar. In combination with my guidelines, this attack WILL become your favourite attack.

SPACE

Face Only one Champion - Karthus - has such an ugly, but also deadly looking face. Look a bit closer and you'll see, that he has some similarities to famous politians who are dead now :(

SPACE

Opponent Noone hates Teemo so keenly like me ...I mean like Karthus. Teemo is stupid and only Karthus can change that almost permanently with his ultimate. Just follow my guide and you'll see why.

Karthus is definitely an AP-Champ, although I often played him as DPS-Tank (which is goood, I can tell you), that's why I've chosen the Runes which were BEST for Karthus. It wouldn't be very epic, if you'd use one of those old, chunky runes which don't even have the potential to bash anyone, so there is only one kind of rune left, the essences. Yes, you've heard me right, I said essences. That's an English word by the way. And because this guide is only written to pro-players like you and especially me, I'm very sure about your possibility of obtaining the right runes.
"But why exactly 244 AP-Essences, 3 Gold-Essences and 100 Cooldown-Essences?", you might ask. That's because WE CAN. Yes... at least I can.
This runes will grant you an instant victory, because NOW you can spam your ulti against all those stupid Teemos on the map.

"But why the heck this stupid Defense-Masteries??", you might shout. The same question I could ask you. Why use Defense-Masteries, when you originally wanted to play an AP-Champ? Because this is only the beginning. Due to the limitations of this platform, I am not able to extend my Masteries with infinite placeable points. That makes me sad, but I can still go on with that.

After a quick look at the items you might just want to switch to another guide. But you're not doing this because this guide is stupid (no, this guide is in fact extremely epic), you're just stopping because you feel too weak to instant-buy Rabadon. Here's the solution:

1. Buy yourself a drink
2. Drink it
3. Repeat step 1. and 2. till you're epicly drunk
4. Do it

As you quickly understand, this is the best and easiest solution for your limited thinking. After that, your mind is still infinite times more limited than my mind, though.

The chosen skill sequence is only a logical consequence from all these strategies above. If you missed these, I'll just summarize them for you:

After you maxed out your ulti on level 18, you'll create some nice dooms day on the map. This will not only erase all your enemies, it will also evaporate any players on the world who are currently playing as Teemo.
Just don't try to kill yourself - after you've instant-won the game of course.

Players from the pro-league (like me) don't even need ANY Summoner Spells. They just spit them out or dug a hole and throw them in, whithout ever using them.
So in theory you could just choose ANY spells, you just MUST NOT use them, or else you shouldn't dare calling yourself a pro.

If I look back at my guide, I really have to praise my good work. This is the far best and most useful and most comprehensive guide out there, featuring unique, limitbreaking runes and skill uses.
Anyone who comes across this guide should try and do what I've told him and he will become an EPIC PRO, just like me.