Ok here we go! Kassadin is burst mage assassin, capable of taking down most of enemy mages, without taking much damage. But before buying Kassadin you should know that he is suited for 1v1 fights(as many other assassins) but kassadin excells at that. He is one of my favorite champions because hes really fun to play and you wont see him so often. ENJOY!

Pros:

+Awesome burst
+Good survivability
+Great chase
+Great flee
+Ungankable after lvl 6
+One of the best mid champions in game
+Fun to play
+Badass

Cons:

-Vulnerable untill lvl 6
-Hard to master
-Low utility skills
-Can focus only one enemy at once

Greater mark of insight is number 1 option for most burst mages and its not different about kassadin.
I take flat mana regen next due to hes early mana problems.
AP next for more dmg and better laning phase.
And Quintessence of potency to boost my magic penetration and dmg output.

Null Sphere is Kassadins main DMG ability and thanks to that spell he is so godlike against other mages due to its silence effect.
Kassadin fires a void bolt dealing 80/130/180/230/280 (+0.7) magic damage and silencing the target for 1/1.4/1.8/2.2/2.6 seconds.


Nether Blade is ability used for mana replenishment and for boosting your melee damage when other spells are on cooldowns. Not so viable, i lvl it up last.
Passive: Kassadin's melee attacks draw energy from the void, restoring 8/11/14/17/20 mana each hit. If this effect is triggered from attacking a champion the amount of mana restored is tripled.

Active: Kassadin charges his nether blade, gaining 30/45/60/75/90 bonus magic damage for 5 seconds.


Force Pulse is your secound damage ability although it deals same amounts of damage as Null sphere, it needs to be charged untill used. Very usefull for chasing due to its slow.
Kassadin draws energy from spells cast in his vicinity, gaining a charge whenever a spell is cast near him. Upon reaching 6 charges, Kassadin can use Force Pulse to deal 60/120/180/240/300 (+0.7) magic damage and slow enemies by 30/35/40/45/50% in a cone in front of him for 3 seconds.


And finally Riftwalk. This is the bread and butter during whole game. It is used to chase or flee and it maked Kassadin one of the most mobile champions in the game. Also it deals some damage and if stacked it can do unbelievable carnage.
Kassadin teleports to a nearby location dealing 60/90/120 (+0.5) magic damage to surrounding enemy units. Additionally, each subsequent Riftwalk in the next 7 seconds costs 100/100/100 additional mana and deals 60/90/120 additional damage.

Starting items:

Saphire Crystal

2x Mana Pot




I start with saphire for more mana early and two pots for hp regen if something goes not as i planned.

1st Recall:

Tear of the Goddess

Boots of Speed



When u first recall u should have at least 945 gold to buy these items.

Mid Game:

Rod of Ages

Sorcerers Shoes


Archangels Staff


By buying these items you get yourself good lane sustain, magic penetration, ability power and most importantly A LOT of mana that u will need to spam your combos and stack ulty in fights.

Late Game:

Rabadons Deathcap

Lich Bane


Rylais Crystal Scepter



And finally u finished your build so you have insane AP, survibability, mana and obviously DAMAGE!

These are the items used for some special sort of situations.

Against heavy AP team:

Banshees Veil

Gives you some more HP, mana and MR. Also great unique ability.


Mercurys Treads


MR and tenacity. Sometimes its much better option than sorcerers.


Abyssal Scepter


AP, MR reduction for nearby enemyes and MR for you.

Against heavy AD team:

Zhonyas Hourglass

Heavy load of AP, armor and unique skill that saves *** and has many tactical uses.


Frozen Heart


Some armor and mana. Also it provides cooldown reduction and reduces nearby enemyes attack speed.

Against tanky team:

Void Staff

AP and magic penetration. All you need against high resist suckers.


Deathfires Grasp


AP, mana regen, cooldown reduction and great unique skill that deals percentage of max HP.
Not really the best item for Kassadin but still you can find it usefull.

Cleanse is spell that really boosts Kassadins survivability and ability to escape all types of ganks. It is the main choice for many players and i recommend it to those that are skilled enought to handle escaping only with ulty.

Ignite is must have spell for Kassadin because it gives you some more DMG early and helps you take down healing enemyes such as Vladimir.

Flash is number 2 choice after cleanse. I recommend it to players that are not so skilled with kassadin. Its easy adn effective and some people prefer it because double flash can be really usefull in some situations.

Good for lane sustain if u are too aggressive and run out of mana fast. Lately it can help you farm or backdoor.


I dont recommend any other spells for Kassadin because they lack the effectivness for hes style of play.

Story

There is a place between dimensions and between worlds. To some it is known as the Outside, to others it is the Unknown. To most, however, it is called the Void. Despite its name, the Void is not an empty place, but rather the home of unspeakable things, horrors not meant for minds of men. Though such knowledge is lost in modern times, there are those who have unwittingly discovered what lies beyond, and they have been unable to turn away. Kassadin is such a creature. He was once a man forced to look upon the face of the Void and forever changed by what he saw. Once a seeker of forbidden knowledge, he discovered that what he sought was something else entirely. He is one of the few that has found his way to forgotten Icathia and lived to tell the tale, following the scant breadcrumbs hidden in ancient texts.

Within a decaying cyclopean city, Kassadin found secrets of the kind that he will never share - secrets that made him quake with fear at the visions of things to come that were thrust upon him. The power of the place threatened to consume him forever, but Kassadin took the only route available to him in order to survive - he let the Void inside him. Miraculously, he was able to overcome the alien urges that went with it, and he emerged as something more than human. Though a part of him died that day, he knows that he must protect Valoran from the things scratching at the door, waiting to get in and visit their torments upon the world. They are only one step away... something to which the appearance of the abomination known as Cho'Gath attests.

"If you look upon the Void, you can't put it behind you. If you look upon Kassadin, he is probably already there."

Quotes

Upon selection

"The balance of power must be preserved."

Movement/attacking

"As you wish."
"Balance above all else."
"I'm on my way!"
"Justice will be served."
"Silence!"
"You are null and void."
"Your magic is powerless against me!"

Taunt

"Try that again!"

Joke

"I tried to silence my mother once. Boy, did I regret that."

V1.0.0.131:

Riftwalk cooldown increased to 7/6/5 from 6/5/4.

V1.0.0.130:

Fixed a bug which caused Force Pulse to cast backwards after performing Riftwalk.

V1.0.0.129

Null Sphere: cast range reduced to 650 from 700.
Force Pulse: damage increased at earlier ranks to 80/130/180/230/280 from 60/115/170/225/280.

V1.0.0.125:

Void Stone: magic damage reduction increased to 15% from 10%.
Null Sphere: missile speed increased to 1400 from 1150.
Nether Blade: base magic damage on-hit increased to 30/45/60/75/90 from 20/30/40/50/60.

V1.0.0.120:

Nether Blade:
Passive base mana restore per attack increased to 8/11/14/17/20 from 4/8/12/16/20.
Active changed to dealing 20/30/40/50/60 (+0.15 ability power) bonus magic damage dealt on hit for the duration instead of receiving 7/15/25/38/50 armor penetration for the duration.

V1.0.0.119:

Classic skin splash art updated.

V1.0.0.118:

Added a gray version of the charging icon for Force Pulse.

V1.0.0.115:

Fixed a bug where the visual for Force Pulse occasionally wouldn't align with the direction cast.

V1.0.0.113:

Force Pulse:
Damage reduced to 60/115/170/225/280 from 60/120/180/240/300.
Ability power ratio reduced to 0.7 from 0.8.
Cooldown increased to 6 from 5.
Riftwalk: ability power ratio increased to 0.5 from 0.4.
Void Stone: damage reduction reduced to 10% from 15%.

V1.0.0.103:

Nether Blade: cooldown reduced to 12 from 15.

V1.0.0.101:

Nether Blade: mana cost reduced to 25 at all ranks from 30/40/50/60/70.
Riftwalk:
It no longer shows cast particles over fog of war.
It now leaves a buff showing the duration of the increased cost and damage of subsequent casts.

V1.0.0.100:

Riftwalk can no longer be cast while rooted.
Nether Blade: level up tooltip now correctly states the increased mana cost.

V1.0.0.99:

Stats:
Attack range increased to 125 from 120.
Magic resistance gained per level increased to 1.25 from 0.

V1.0.0.96:

Nether Blade has been redesigned:
Passive: Now restores a flat 4/8/12/16/20 mana with every hit and triple this amount when the hit is against champions instead of removing 2/2.75/3.5/4.25/5% of his opponent max mana and restoring twice that amount to his own mana.
Active: Upon activating the ability Kassadin gains 7/15/25/38/50 armor penetration for 5 seconds.
15 second cooldown.
30/40/50/60/70 mana cost.
Activating this ability counts as a spell cast for the purposes of Force Pulse.
Null Sphere: projectile speed increased to 1150 from 900.
Void Stone:
The attack speed effect now stacks and renews instead of being replaced on spell impact.
Duration lowered to 4 seconds from 5 seconds.

V1.0.0.70:

Void Stone now applies an additive attack speed boost, rather than multiplicative.

V1.0.0.61:

Force Pulse: ability power ratio reduced to 0.8 from 1.

V0.9.22.16:

Riftwalk: mana cost reduced to 100 from 110.
Force Pulse: charge number requirement increased to 6 from 4.

V0.9.22.15:

Armor per level reduced to 3.2 from 3.5.
Null Sphere: ability power ratio reduced to 0.7 from 0.8.
Force Pulse: now gains charges whenever any nearby champion casts a spell.
Sounds:
Reduced volume of Null Sphere and added volume/pitch randomization.
Decreased the volume and radius of Force Pulse "Can Cast" sound.
Increased the volume and added volume/pitch randomization to Rift walk.

V0.9.22.9:

Riftwalk:
Mana cost increased to 110 from 75.
Cooldown increased to 6/5/4 from 6/4.5/3 sec.
Doubling time increased to 8 from 7 sec.

V0.9.22.7: Added

Null Sphere: Kassadin fires a void bolt dealing Magic Damage and silencing his target.
Nether Blade: Kassadin's physical attacks steal a percent of his target's mana, and he gains twice the mana drained from these attacks.
Force Pulse: Kassadin draws energy each spell he casts. Upon reaching 4 charges Kassadin can use Force Pulse to deal Magic Damage and slow enemies in front of him for 3 seconds.
Riftwalk (Ultimate): Kassadin teleports to a nearby location dealing damage to nearby enemy units. Additionally, multiple Riftwalks In a short period of time cause them to cost additional mana and deal additional damage.
Void Stone (Innate): Kassadin takes 15% reduced damage from abilities and transforms this damage into bonus attack speed.

I will try to keep this build up to date and maybe to add some content later. If you have any suggestions feel free to comment and ask.

-updated mastery tree
-updated spells