Kassadin is scary as balls. Nuff said

It is a must to get Magic Penetration Marks since it will not only give you massive damage early game(don't forget the mastery bonus) but also late game

Mana Regen Seals are very useful for laning, allows you to keep spamming your spells

For Glpyhs I chose Ability Power/lvl instead of Magic Penetration because after doing several calculations, combination of AP and M.Pen deals much more damage then pure M.Pen

And lastly Quints, I like using Health Quints since they not only synergize with my Veteran's Scars(mastery: 60hp) but they also make Kassadin look more intimidating early game

I used to go standard caster's 9/0/21 until i read a guide Kassadin - Way of the Void, now i go 9/21/0
"Strength of Spirit really is awesome. It gives 0,3% of your mana per second. So 1,5% per 5. 1000mana = +15hp/5. Every 1000mana you get a free Regrowth Pendant, worth 430gold"

Strength of Spirit gives INSANE health regen/5 and will allow you to lane for a really long time, or to recover quickly from a team fight
[EDIT] Now it only gives 1% of your mana to health regen/5-but still nonetheless a really great mastery

Ardor is a great hybrid mastery, even though we aren't going hybrid, but the extra +4% Ability Power is a great add-on to Rabadon's Deathcap

Tenacity synergizes very well with your passive (Void Stone: Kassadin takes 10% reduced magic damage and transforms this damage into bonus attack speed) so you receive much less damage

Archaic Knowledge in offensive mastery is pretty self-explanatory, a lot more M. Pen

Alright, I'll give you the intricate breakdown of which items to get and when
I will discuss gameplay strategy later on
this build is REALLY offensive with almost no defensive items, but if you truly do feel you need some defense/health then buy either a Warmog, Force of Nature, or Banshee Veil[Usually the best to get] right after your Mejai Soulstealers
Generally once you master Kassadin, you won't have too much to fear about getting CC'd to death, just remember, stay hidden and wait until your tank gets attacked

Core Build


When going to lane, pick up 2 HP pots and a Sapphire Crystal

Your first trip back to the store, buy Boots of Speed and Tear of the Goddess if you have enough

Then buy Mejai Soulstealers for them stacks, this will be your main source of Ability Power for a while [When I play Kassadin, I generally always buy this stacking item, even if I'm doing bad, because once you do get a couple of stacks on it you are kinda unstoppable - but if you don't want Mejai's then instead build straight into Rabadon's]

Buy a Needlessly Large Rod, but if you are only within range of gold by 100 then save up
If you have just enough for Blasting Wand then go for it
If you don't have enough for either, then buy Ionian Boots of Lucidity

At this point just build into Rabadon's Deathcap

Then complete an ArchAngel's

Buy a Sheen instead of a Blasting Wand, because at this point some extra attack damage will be more useful
Build straight into a Lichbane - your now a 3 hit turret killer and able to deal damage both magic and physical damage[This will scare those tanks that decided to stack only Magic Res.]

I've rarely ever made it to the last item because the game always ended too early
This is the kind of item when both teams are neck at neck
Very situational, choose your last item to counter your enemy
If they have a lot of Nukers, get either Warmogs or Force of Nature[They both synergize with Strength of Spirit]
If they are mainly tanks, go for a Void Staff
or if they are balanced between casters and tanks, an Abyssal Scepter will work nicely
If they have a fed heavy dps, get a Thornmail
If they have a fed attack speed tank ripper, get Frozen Heart

Early laning, Null Sphere hurts a lot

Late game, Force Pulse hurts much more[Slow % is higher and AP scaling is higher then Null Sphere]
[EDIT] After the Kassadin debuff, Force Pulse AP scaling is the same as Nullsphere so now I leave FP at lvl 3 and max out Nullsphere first since they deal the same amount of damage

Riftwalk, self-explanatory - always max our your ultimate first

The only use for Nether Blade on AP Kassadin is to proc lichbane or add stacks to Force Pulse, max it last

Why not get one on Nether Blade to proc Force Pulse quicker?
Because sacrificing quality of damage for frequency of damage is not worth it, also in laning you shouldn't use Force Pulse often since early levels dish out very low damage and the mana cost is high

Clarity: People may say "this is a noob summoner spell" or "it will only gimp your killing ability"
In a sense it may seem true, but here is the way I use it to kill/save
During laning, when you are CONSTANTLY throwing your Null Sphere at their face they will most likely be very low health once you have your ult and you will be at low mana, simply use Clarity and you can continue your constant harassing or jump in for the kill
When you are chasing or running away and you are at very low mana with some stacks on your Rift Walk[Casting Rift Walk often increases mana cost amount by quite a bit] use Clarity and cast that final, or multiple, rifts.
This is also useful for team fights when your teammates are at low mana

Ignite: Great for killing, and great to prevent their health regen from working[For example Mundo's Ult, Vlad's heal abilities, Warwick's heal, etc]

Cleanse: This is an option if you are a more cautious player, very useful overall if you are in a tight situation[If you get stunned/cc'd, Cleanse and Rift Walk out]
If ooming while laning was not a problem, I'd definitely take this Summoner Spell along with ignite

Flash: Another viable spell, this will allow quicker chasing and a safer way to tower dive. Personally the only reason I don't use this spell in place of Clarity[Personally I keep Ignite because the damage output] is since the overall cooldown is pretty long and the range is not too big[Must be directly next to the wall to jump it], I'd rather wait another 3 seconds to recast Rift Walk

Heal: Definitely another viable spell, great for team fights, savings yourself/teammates, or tricking your opponent into thinking you are low on health. But a pretty big downfall, besides the long cooldown, is if you have Grievous Wound[Health regen reduced by 50%] the heal itself is reduced and you will not receive the full benefit.

My basic laning rules until lvl 6
-Take middle lane
-Don't use a health potion unless you are under 25% health
-Dont spam your Q ability until it is lvl 2[The damage vs mana cost isn't worth it yet]
-Don't use your E at all...unless you know it will secure you a kill[Early game, it does very little damage]
-Don't push hard if they have a jungler, push enough to keep pressure
-In some cases, don't hurt them too much[Enemy may go B and it will lose you a kill - get them at least to 30% health]
-If they are a caster without clarity, from lvl 1-2 purposely make them waste their abilities on you[This makes them oom faster and will allow you to kill them more efficiently later on]
-If they can heal a lot/prevent your harassing, don't waste time harassing them[Champions such as Nunu, Nidalee if she maxes her heal, sometimes good Vlads]
-Only last hit minions
-Wait until at least lvl 4 to use Clarity, make sure your mana is REALLY low before using so you won't overheal your mana
-Dont B until you have your ult

After lvl 6
-If they are under 50% health, kill them[Basic combo: Riftwalk->Force Pulse-> Null Sphere->Ignite]
-Only tower dive if you have more than 50% health and know you can get the kill
-Don't use your Riftwalk to be your source of damage[Don't always have to land the aoe on them, at least get yourself into a good position to use your Force Pulse]
-When traveling back to lanes from nexus, cast Riftwalk once to give you a small boost[Not multiple times unless you have golem, over the course of travelling your mana will regen]

Kassadin has had a horrible reputation to be a KSer, but in fact he really is not - it just appears to look like he is KSing

Basic Combos to cast Force Pulse
5 Stacks: Riftwalk->Force Pulse
4 Stacks: Riftwalk->Null Sphere->Force Pulse
3 Stacks: Nether Blade->Riftwalk->Null Sphere-> Force Pulse

Ganking
-Wait to initiate when you are able to combo into a Force Pulse[Unless your teammate initiated then follow through]
-Stay hidden in the bush
-Remember, jumping through walls let you travel farther than jumping in the open[Even certain walls that are farther then your ult distance will allow you to hop over it]
-Always get their carry/squishy[That's what Kassadin is made for]

Teamfights
-When two sides haven't fought yet, wait patiently in a bush or behind a wall to give the enemy false appearance of enemies
-When there is a brawl, don't jump directly in the center of the action or you will get caught in the crossfire
-Hit the priorities[Carries, Fed, Squishies, not Tanks]
-When casting Force Pulse, hit as many as you can
-Use your Force Pulse to slow running enemies for your teammates
-Silence their channeler or heavy caster
-Always help your teammates if they are running away, even if you are low on health[You can Force Pulse and Riftwalk away safely saving yourself and your friend]

Notice: All my matches are with a level 30 summoner and if I ever did premade a group they are level 30 as well, I don't pubstomp on lower levels
After Kass Debuff
[Force Pulse Damage reduced to 60/115/170/225/280 from 60/120/180/240/300
Cooldown increased to 6 seconds from 5
Ability power ratio reduced to .7 from .8
Riftwalk ability power ratio increased to .5 from .4
Void Stone damage reduction reduced to 10% from 15%]I was messing around with dps/hybrid/hybrid tank/all zeal from games [30/11/15] - [13/6/8]tankadin.