Kassadin Runes explained
There's one set of runes for Kassadin on patch 15.4 that is the clear favorite for LoL players and pros alike. The best Kassadin rune paths on the position 
Mid are 
Domination as the primary path and Sorcery as the secondary path with a pick rate of 41%. Besides picking runes on Kassadin you should learn how to play Kassadin and if you are interested in pro matches take a look on how a pro builds Kassadin. If you want to discuss 
Kassadin then you should visit the champion subreddit.
Kassadin runes from primary path
Domination improves burst damage and assassination tools on Kassadin. Most of high elo players – and our LoL pros in the the major regions – have agreed that Electrocute is the best keystone rune to run on Kassadin. This keystone rune provides burst damage, aiding them in nuking down the enemy carries. Other primary runes on Kassadin are Sudden Impact, Grisly Mementos and Ultimate Hunter.
Sudden Impact increases your damage after dashing or being invisible. This is due to how easy it is to activate on Kassadin with the amount of ways he has to dash, jump or going invisible. The additional lethality helps to take down the priority targets that much easier. Ultimate Hunter scales up Kassadin ultimate haste on every unique champion takedown.
Kassadin runes from secondary path
When it comes to your secondary path, most Kassadin players prefer to go with Sorcery. Sorcery empoweres abilities of Kassadin and increases the available champion resources. On the Sorcery path, the best runes for Kassadin are Axiom Arcanist and Gathering Storm.
Axiom Arcanist grants you a shield, as soon as Kassadin gets hurt by alot of magic damage. This rune will help you alot to survive against ability power champions with a lot of burst damage. Gathering Storm increases your late game power.
FAQ for Kassadin Runes
Which is the best keystone rune on Kassadin?
The best keystone rune on Kassadin is Electrocute. This Kassadin runes setup is then referred as Kassadin Electrocute.
What runes does Kassadin use?
Runes from the paths Domination and Sorcery are the most used runes on Kassadin. For the exact pick rates of Kassadin runes used, you have to study the rune distribution presented.