I gave this a +1, but I still dislike the item Archangel's Staff. Also, 2 Rod of the Ages looks a bit unnecessary. You could, definitely, get Banshee's Veil instead of one of them.

Edit: Also, have 1 spot for Void Staff no matter what, seriously. Probably instead of Archangel's Staff or 2nd Rod of the Ages, but have a spot for it regardless.

LOL I CAN DOWNVOTE GUIDES TOO SEE
HAVE FUN WITH NO DAMAGE AND A FAILED GAME

BOOM! MANA-DIN! +1

Maybe you should use some coding and more colors.

Banshee's is definitely a viable item on Kassadin. If you want one, you can easily replace one of the RoA for it. I prefer the second RoA, but that's just me. I'll put it in there as an optional item.

Very nice. I like the defensive masteries, I agree that Offense and Utility don't really have much to offer Kassadin. Backdoor Kassadin is an interesting idea, I'll have to try it sometime. I personally prefer Cleanse instead of Exhaust - Since I'm already in the defensive tree, I can spare a point in improving it, and it's saved my life a couple times, but if you're really set on taking Exhaust, it would help your team more in fights. Overall a solid build, +1 from me

Too easy game build imo

Good build but maybe you should try a Banshee's Veil it works for me anyhow i gave you a +