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.
After paging through the cheat sheet, I know what you're thinking - This kid's crazy, right? Wrong. Instead of blow if off, try it once and tell me what you think in the comments. In my opinon, Kassadin was made to be a melee dps. Look at it this way - Kassadins spell's are that of the best melee dps champion. All melee champs have ways to close the gap between them and their enemy. Kassadin can flash in, slow them, silence them, and after all that do some ridiculous melee dps. The enemy, slowed and silenced, will die. They cannot escape, because of Kassadin's ult. So now that you know how ridiculously good he is, let's go over how to build him
Standard melee dps runes. Desolation marks and quints for more damage, armor seals for early game squishyness, and mana regen glyphs for a low mana pool early game.
Once again a standard melee dps. I take points in defense instead of utility to help with Kassadin's early game and the mana regen also helps a ton during the laning phase.
I find these items to work the best on Kassadin. I start with a Doran's Ring because before your Madred's, spells are your main source of dps. The mana regen also helps a lot. The Madred's is a must for me, and it is also why i build so much attack speed. The Banshee's endgame is for survivability, so you can save your cleanse to use again in another sticky situation. I suppose you could swap it out for an infinity edge if you're destroying the enemy team.
Early game (Laning Phase)
Try to focus most on last hitting during this part of the game. The earlier you get a Madreds the better, as it is your core item. If you have trouble with enemies harassing you, its ok to blue pill early and grab a potions and boots. When you hit level six, you have your opportunity to get first blood. If you have a jungler, signal him that you're ready to gank. Flash in, slow and silence the enemy you're going for. If your team has a stun, great. Regardless, pop your w and wail on them until they are dead. Use any spells as they come off CD, because your attacks arn't as strong in this phase of the game.
After a tower or two is destroyed, you enter the mid game phase. Hopefully by now you have your Madred's and your on your way to a BF sword. Keep on farming your lane, only departing to gank, for teamfights, or when the minions are too far pushed (If a teamfight is happening far away, feel free to keep pushing. Kassadin is a great backdoor champion, because he can flash away after killing a tower quickly).
The most important thing to know how to do is Kassadin is when to get involved in a teamfight. If you flash in first, you will die. Let your tank go in and let a few ultimates get busted, then flash on their carry. Slow, Silence, and pop your W. They will be dead quickly, and hopefully at this point you can keep jumping around the fight doing some damage. Remember to use your Q and E, because they are great at controlling a teamfight.
If your team has won, chase down the enemies that are running away with flash, slow them and destroy them. If your team has lost, flash away and defend/go back.
Remember you are a great backdoor champ, so if the enemy is occupied somewhere else don't be afraid to run up with that creep wave and blow up a tower.
Blue Buff - Yes.
"But I'm not AP?! I don't need?!"
False: Blue buff allows you to spam your ultimate and your crowd control spells. Nothing is more dangerous than a fed Kassadin flashing around the map.
You have the same role in teamfights as described in Mid Game, jump their carry and kill them. If they are too well protected, flash around the back of them after their tank has initiated.
Don't blow AS/AD Kassadin off, he really is great. He is a fun melee dps who can destroy the enemy team if played correctly.