Everbody know Kassadin the Voider. He's a Caster Burst AP mage. Maybe guys wont like my Guide but i have a different playstyle like the normal Meta. (and i hate META). Kassadin main job in my hands is that: KILL PAPER ENEMY DMG DEALER or dealers :3 So yes its a harrashing and aggressive build with some hp.

Pros's:

• One of best Mobility champ in LoL
• Good CC-s Silence and Aoe Slow
• Passive awesome (-15% magic dmg)
• Nice Burst

Con's:

• Hard and slow early game until lvl 6
• With wrong Build easy die
• Late Game cannot Kill a good Tank

Talk about spells firstly:

• Ignite : This spell dealing True dmg what is usefully for
  everbody. Becouse Kassadin a Burst Dealer so
  ignite help a lot for fast and easy kills.
• Cleanse: Cleanse pure your body from every negative status
  effect and last 3 sec u get -65% CC effect. I
  choosed this spell on second spell, becouse in
  fight can save your life. U get Stun? Silence?
  Taunt? Knock? Or DANCE? ye just use your Cleanse
  and get away from focus or from raping time with
  your ultimate.
• Flash: I hate and laugh on every Kassadin who use this
  spell thats show they are newbies with Kassadin.
  Becouse why u use a flash (300 sec Cooldown) when
  u have 4 sec ultimate which is better then flash,
  so strange isnt? Again: Flash USELESS....
  
• Barrier: U arent a Paper useless ADC u dont need barrier to
  save your Voiding *** :P
  
• Teleport: Maybe Usefully with fast hard Ganks, but just
  look the map and your teammates and going there
  with your feet khmm,,, we dont have feet so
  whatever xD just go there and help. Waste spell.
  
  
• Heal: U are Not Support or Defensive U ARE AGRESSIVE
  KILLER.
• Exhaust: Its a good spell who rly 100% kill your enemy
  Dmg Dealer. I played a lot with Exhaust Ignite
  Combo. But Exhaust useless if get Stun or Silence
  so still.... Use Cleanse save your life trust me.
  
• Clarity: Ahahaha HAhah hahaha HA... (Laugh >_>)

So We had a Wood-PC so had enough time to talk some other things.. like Runes. I Tried a lot which is better Magic Pen, AP, HP, Magic resist on mid... And of course Pure AP is best for Kassadin. Thats my Opinion sry. MAgic pen same good, But Kassadin is Burster so just take your full AP rune page and kill your enemy.

The real reason how get Pure AP Runes is that Kassadin has 2 high AP rate Skill, Q: Null Sphere (70%) and E: Force Pulse (70%)

yes 90%, we got more little time how we talk about the masterie page. I use 22-0-8. hmm nothing more xD just use this.

Lvl 1- Lvl 6 : I start with Ruby Crystal, So i get high hp on start. If enemy on mid is mellee u have easy way to farm and u can poke him with Q. If your Enemy is Range now... u will get low farm xD but man Kassadin dont need Minion Farm. My motto is "Farming on enemy Champs". So u must wait the lvl 6 and farming with Q and sometimes E if u get the charge isnt hard. Kassadin in early is calm game. Just wait farming and get lvl 6.

Lvl 6+. Rush For RoA not for Tears of Goddess. My experencie is that, Kassa who start with Tear of goddess lose their match in 80%. Becouse Kassadin easy die if get Focus so be a Little Tanky.
After u Get RoA get Other items what u can see in builds. After u see u can carry your team with Kassadin suddenly buy a Mejai if u cannot, Take Rylai.

Other items: If your enemy Team has too much Tanky and They carry the Game get items which help u for Killing Tanks, Sadly KAssadin isnt a Tank killer so u cannot do much. Thats time u must buy Deathfiregraps, Liandrys Torment, Blade of The Ruined King Blade. Maybe Ad- items crazy for u guys, but Kassadin with 500-600 AP more then enough to Rape enemy ADC or AP carry. With this amount of AP u easy burst down enemy ADC fully. So after u get this AP u can buy some other item for your AD. (W is help a lot for u same)

Hmm now thats all. I will Upgrade The Guide if i get More time. (More info, More Pic. Video. More Visual Upgrade) But Still can Comment if u have some question.