This is an incredible build, with a ridiculous amount of cohesion between runes, masteries, items and playstyle. It is also not too expensive which has always been a weakness for traditional Kennen builds. It is tanky, and is good for pretty much anything, whether kiting ad bruisers, split pushing, winning team fights, assassinating carries, saving team members.. this build can do it all

Kennens mid game is already very strong, so when you can rush through that solari your whole team can tower dive along with your ult. It just destroys enemy moral. Having -40% CD, Barrier, Solari, Zhonyas and your ult, you are a fearless team-fight-winning machine. I have played Kennen for over a year and this way, thanks to the new patch, is by far my favourite.

I hope you try it and love it too!

Thankyou

IMPORANT - This site doesnt seem to have the Flat Energy Regen Seals. I use 6 of those, and 3 of the scaling energy regen seals. DO NOT USE 9 SCALING ENERGY RUNES!

This kennen build is all about overwhelming presence, and will build another 30% CD in addition to the 6 from runes and 4 from offensive mastery, to max at 40%. To spam those abilities at low CD's, the energy regen is totally necessary.

The new mastery trees are very good for Kennen. There is something great in each tree for him, and you dont need to delve too deep. Magic pen from offense is a must, CC reduction from defense is equally important as you build not tenacity and Kennen should be slick to escape from his ulti. (although with this build he is not so fragile.) Lifesteal and spellvamp are helpful in early game as Kennen uses both equally.
Movement speed is great for his E, and to get back behind minions in early game if you harass with E. The summoner spells cooldown is important because Kennens strongest initation on a whole team is to flash in and E before R. Lastly you will be buying 2 items with activated cooldowns, so the CD reduction in "Artificer" is perfect.

For this build i have had alot of success going B very early in the game, in the region of 450 gold to get that kages pick and 3 or 4 health potions.
Before you head back, you can work the enemy down a bit, knowing your health will be regenerated at base and you will be buying potions to give you the sustain needed to farm solidly for the next 5-10 mins. You can spam your E to get back in lane quickly. Often at this time you can get your first kill, due to the harass you did before you went back, and the AP/regen advantage.

You should now farm hard for your Liandrys, and soon after be buying an Iron Solari.

With your Solari and Lianry's, you will be leading the rush with your team, popping your Barrier summoner spell for yourself, and the Solari for your whole team who will naturally be with you to profit from your ulti. You can get your full combo off, while turret diving, and then chase up any running survivors.. The solari is SO good on Kennen, when you get it, it really swings the mid game.

Get a Zhonyas and troll even harder. with your barrier, Solari, Zhonyas and low CD ghost, you are exceptionally hard to kill. This is where you can start to have fun. There is always something to do, no idle time playing Kennen.

This is where things are most fun for you. It is rare that the game lasts too long due to the strength of this build, but if it does, you can build a WOTA so you can be EVEN MORE audacious, and keep your hp high enough so you never have to back down in long team fights. After that you can finnaly cash in your Pick for a Morellonomicon, and enjoy 40% cooldowns, which means your ghost escape is on a 3 second timer, and you can split push better than anyone in the game due to how much map coverage you have. (if you needed to, but you will conitnually win team fights so wont have to).

Also at this point you have both the liandris passive and morellos passive and you can set a whole team alight with both just from one E on its 3 second cd, so even though you arent packing a Rabadons, these two passives allow you to deal tonnes of damage easily, and safely, and your damage output is less reliant on your ulti.