This is my build for kassadin
My Main Build;
Spells: Clarity and Teleport (for side lanes), or Ignite (Mid)
Other good spells include flash, exaust and heal
Runes:
-Quints of Potency
-Marks of Insight
-Seals of Clarity
-Glyphs of Force
Items:
1. Boots of Speed + 3 Health Pots
2. Rod of ages or 2 Doran's Ring (if doing really really bad) (Its better to pick up Rod of ages Before the 18 min mark so it stacks)
3. Sorceror's Shoes
4. Rabadon's Deathcap
(If cant afford Needlessly large Rod quickly, DON'T SAVE UP FOR IT, Get a few Blasting wands. you need the AP output)
5. Void Staff or Banshee's Veil (Bad)
6. The one from number 5 you didnt get
Abilities:
Null Sphere
Force Pulse
Null Sphere
Force Pulse
Null Sphere
Riftwalk
Nether Blade
(After this you have a choice Rank up Null Sphere (Silencing) from here or Force Pulse (more damage)(Do both before finishing Nether Blade)
Finish Rift Walk and end with Nether Blade(last)
Nether Blade is Kindof Pointless. The only real purpose that most players us it for is stacking Force Pulse.
Basic Combo:
Rift Walk
Force Pulse
Null Sphere
Ignite (if applicable)
Rift Walk again (Away from fight if needed or towards enemy if they are low)