Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This build is my all time favorite kassadin build, try it out and you will clearly see why kassadin is one of the best heros in LoL. Played properly you will never die and gain double digit kills every game. wether your team is losing or winning you will still be the one topping the charts. most games will not go longer than your zhonya's so you will find buying pots is more useful any of the last three items will be useful but after 20 stacks if you maintain a pot or blue buff you have max CD reduction so you will be rifting every 2.4 sec
If you want go leviathan aswell it is extreamly useful if your ganking like crazy... basicly ensuring your unkillable self to never be killed.