Hey guys, this is my DPS Kassadin guide. This is kind of a response to a dps build I saw earlier today. Seeing dps Kassadin (rarely) be played, I've realized that the insane burst damage done by kassadin can be greatly extended by adding a slight amount of survivability. The focus of my build is the crazy attack speed burst you receive from taking magic damage. Being able to take MORE damage from AP champions only makes you more efficient at slaying enemies. This is my attempt to show everyone how to, in my opinion, correctly play Kassadin.

Greater Mark of Magic Penetration & Greater Mark of Desolation - For runes, I pick up BOTH Armor AND Magic Pen marks. This is because, as a hybrid dps, you deal damage from both sources. Neglecting one only leads to a lopsided damage load. If the team stacks armor vs. your armor pen, your magic pen would be quite weak and unable to compensate.
Greater Seal of Replenishment & Greater Seal of Alatricy - I also pick up flat mana regen seals, as well as AS seals. This is because mana tends to be a problem when I see people playing Kassadin, especially early game.
Greater Glyph of Magic Resist - For glyphs I grab magic resistance just to benefit my passive skill. I'll take 2 attack speed quints as well as a flat hp quint to assist in early game squishiness.

Why Cleanse? Kassadin can JUMP?!
I take cleanse because CC'ing Kassadin is crazy easy, and normally results in a kill for the other team. When Kassadin ults in to a teamfight, he leaves himself vulnerable for a few seconds until he can jump back out. This tiny interval is just enough for (sion) to stun you. Cleanse eliminates this problem by giving you an anti-CC spell.

I do use weird masteries playing Kassadin. This is because I feel Kassadin is way to mana hungry, and squishy to ignore regen and defensive stats. I also take 21 points in offense because this only makes his effectiveness better. 21-6-3 is kind of experimental, and feel free to grab dodge if needed, however you will NOT be a sitting duck and have a need to dodge an attack.

-Kassadin's strong point is Mid/Late game. His burst is very bad early, and as a squishy melee, you need to be extremely cautious while laning. Your goal in the lane is not to get the most minion kills, but to harass the other team, allowing for easier last hits when available. using your melee range, and extended spell range, you can zone that annoying (mordekaiser) away from your minions.
-Mid/Late game, you should have Manamune and be building toward your +1000 mana. This is why manamune is so great. You take 2% the end-game 3900 mana, resulting in 76 extra attack damage(Kassadin also has one of the highest base AD's in game) combined with your hextech, and your near max attack speed and you will burst enemies without spells! Continue along the item track, grabbing AD/AS over AP on hybrid items, and push your way to victory!

While most people overlook the effectiveness of Nether Blade and Void Stone, the armor pen gained from activating Nether blade and the attack speed buff from Void Stone is why AP Kassadin is a complete waste of 2 skills. When fighting, your sequence should be R-->Q-->W-->auto attack-->E-->R(chase)-->Q(if needed)-->R(escape if needed)