Kennen is sick, that is all there is to it. He stuns so fast and hits so hard with such low cooldowns that he can take take down almost anyone within 5 seconds. I will show you how. Before we get into the meat of the guide, check out the stats of my recent games. This is after the slight nerf of kennen that resulted in mark duration of 8s and a decreased range of his 'w' skill. The recent nerf does increase the difficulty of early game harass, but makes no difference late game. This is how I play Kennen, try it out and leave comments.

Magic penetration for a pure AP build, self-explanatory.

Good for a squishy character. You could also go with hp seals, it doesn't matter too much.

Kennen's spammable abilities are made even more annoying with lesser cooldowns. This makes it easier to add marks on opponents and continually harass, especially early game.

This will help you hit harder early game.

I go 9/0/21, optimized for cooldown reduction and magic penetration. Your goal is to strike hard and fast. You already have an innate defensive buff with lightning rush, so your masteries are better spent in utility imo.

This is a personal preference. Oftentimes my early game harass will leave the enemy with relatively little hp. Also, because I am constantly harassing, they will usually already have marks already. Here's where this helps -- 'e' lightning rush into range, hit 'w' (electrical surge), and ignite them at the same time. This can be done as a tower dive as well. When the enemy is low enough health, this will get you a kill and keep you safe.

Other masteries to replace ignite are up to your personal preference and play style. I do not get because I already have lightning rush which is similar to ghost. is also unnecessary because you can run to wherever you need to go to pretty fast.

This spell is mandatory. It lets you ambush people with electrical rush flashing on top of them, which adds a mark. Then you can ult and use electrical surge repeatedly for the win. Also good for escaping.

I will explain to you why I choose to max first and over .

'q' Thundering Shuriken Great spammable skill, already has very low cooldown at level 1. I realize that as far as one-hit spells go, this does the most damage; however, the shuriken is easily blocked by creeps, and fairly easily dodged, so the other skills are more useful at an earlier level imo. I use it merely to add marks.

'w' Electrical Surge This is the most annoying skill for enemies. It adds a mark and does damage to whomever is within range. At level 4 skill (previously at level 2), its cooldown is less than the duration the marks remain on the enemy, so you can constantly have marks on the enemy. I max this first because the cooldown decreases by 2 seconds with each skill level increase. This skill also makes it such that every fifth autoattack of yours will add a mark.

'e' Lightning Rush This skill makes you move super fast, ignore pathing, and conveniently boosts armor and magic resist. It is great for engaging in battle, running away, or just adding marks. I max this skill before shuriken because it is more important to be able to move in and out of battles quickly than it is to be able to throw a random high damaging shuriken that may or may not hit whatever you need it to.

'r' Slicing Maelstrom Wow this ult is just ridiculous. Randomly does huge damage and add marks to enemies within its AOE. It also has a relatively short cooldown, which we can use to our advantage, which I will describe in battle strategy.

(innate) Mark of the Storm This is what makes Kennen so deadly. Every three marks does extra damage and stuns for a duration. It almost guarantees raping of anyone 1on1, and most times 1on2 if they are squishy.

Core Items


Secondary Items
I think of this as a core item that should be obtained early in the game; however, if you have trouble staying alive and maintaining stacks, then I would skip this for now, and continue with the core items above.
Adds MR and AP. The MR is crucial as magic nukes tend to do the most damage to you and are the hardest to escape.
A popular item, especially with the spammability of kennen's spells. Doesn't add as much AP as I would like, and so I prefer some of the other items over this.
Good if you have problem surviving. Also good if you're up against someone with an disabling ult that can almost one shot you (i.e. Malzahar)

First of all, Kennen is and should be a carry, and should go mid.

Early Game (Lvl 1-6)
Start with Doran's Shield and 3 health pots . These will ensure you can stay in lane. Add a level to thundering shuriken and head mid. Use 'q' to check bushes.

Harassing: First push the creep line to level up to level 2 ASAP. You can try to hit the enemy with 'q' but anyone who knows how to fight against Kennen won't be in the line of fire. When you are level 2, add a point to electrical surge 'w', and then you are ready to harass.

First, autoattack anything until your next attack is charged. Then, when the enemy gets in range, normal attack him and immediately hit 'w' afterwards. That's an immediate 2 marks and a good amount of damage. The marks will run out before you can electrical surge or build up a charged attack again. It's ok, just keep repeating this. When you get to lvl 3, get lightning rush. Now you can rush in and out of electrical surge range easily.

Here is a good tip for adding marks against a passive/defensive enemy. Charge up your autoattack. Lightning rush into your attack range, hit 'e' to get out of lightning rush, and then normal attack the enemy (be sure to hit 'w' afterwards to surge). Also if the enemy is low, you can add ignite after this to do a devastating combo that usually takes out at least 1/3 to 1/2 of the enemy's hp, either killing them or crippling them so they have to go back to town.

If you find yourself getting outplayed, just hang out defensively, Doran's shield will help you regen, and you can still spam with shuriken.

If you have not killed the enemy by the time you get to lvl 6, now is the time. Even without any marks on the enemy yet, here is a good combo (it will take experience to know whether the enemy is someone you can dive in against. Most enemies without stuns are likely to be easy targets)

COMBO:
1) 'e' lightning rush towards your enemy. If he is not close, then flash onto him. (+1 mark).
2) Immediately hit 'w' and 'r' at the same time. Your ult should hit him three times, thereby stunning him.
3) At this time, ignite him, and try to hit him with shurikens.
4) Keep tapping 'w' to activate electrical surge when it's ready.
5) This combo usually results in a kill for me.

Mid Game (Lvl 7-12)
After you have killed your mid opponent, you should have at least 1235 gold to buy mejai's soulstealer . I get this first because I get a lot of kills very early and having those added stacks early makes you ridiculous (I think my best one was 20 stacks by 18 mins). If you have money left over, buy boots, and upgrade to sorcerer's shoes. Now go around and gank people with the combo above. You can also farm very effectively by lightning rushing through the minions, and then 'w' them.

Note: Do not be afraid to use your ult! The cooldown is pretty short especially with your runes and masteries. Pop in with the combo mentioned above, and you'll get kills and add stacks. With your nuking ability, you do usually get the last hit and can add +2 stacks. Continue the item progression as listed at the top.

Late Game (Lvl 13-18)
You should be at fairly high stacks now with a LOT of AP. Use elixir of brilliance if you find yourself with 250-500 gold in town where you can't really buy anything else. Try not to die. If you have zhonya's hourglass, you can initiate battles very well. Lightning rush in, tap 'w', pop your ult, and then activate zhonya's. You'll demolish all the squishies before they can even touch you. Pick off any survivors.

Pros
[*] Devastating nuking ability
[*] Able to get in and out of fights quickly
[*] Easy to farm
[*] Decent survivability
[*] Carry

Cons
[*] Still squishy, prone to stuns
[*] Normal attacks are pretty much worthless
[*] Losing stacks may break your momentum

Just wanted to share with you all the way I play Kennen. Let me know if you have any suggestions or questions. I will be happy to update the guide to include whatever I am missing. Thanks!