Okay, this is going to be an ongoing and ultimately comprehensive guide to playing Kassadin, so if you find this build enticing then check in frequently as I'll be updating this regularly.

So, KASSADIN aka KASS aka KDAWG. Why him? He is one of those rare LoL champions that truly shines in capable hands (along with Shaco, Ez, Eve, etc). He has the potential to be an utterly dominant and destructive force when played right, but so many people do him the injustice of playing with suboptimal builds.

Why is my build different? Two words: LOTS OF MANA.

Why is LOTS OF MANA a good thing? Two words: RIFTWALK.

Riftwalk is certainly the crux of any good Kassadin's arsenal. The damage it provides later on is jawdroppingly, ********ingly amazing. It gives him mobility, the kind of mobility that lets you engage with 10% of your max HP and (if played correctly) survive.

So the 9 is pretty standard.

Now I explain the 21.

Why Utility Mastery? BLUE BUFF. GET IT AS EARLY AND AS OFTEN AS POSSIBLE. If you manage to maintain Blue Buff starting from about level 10 or so and make use of it (Rift Walk for the Tear effect) you will have maxed out the tear mana cap by Level 16 or so.

I don't get quickness because Kass is mobile enough, in my opinion.

Ignite - It's great for Kass early game, as it compensates for his relatively weak nukes. With proper harassing in the lane, I can usually land fb with ignite when timed right.

Cleanse - Personally I think cleanse compensates for all of Kass' faults (i.e that he is squishy), but it is situational. If you're playing a ranked game and can see their team has no CC, opt for something else.

Flash - I think this is secondary to cleanse, it gives Kass an oh**** teleport that can be used in conjunction with Riftwalk offensively or defensively.