Hello!
My name is Delthion, or Basmadra in League. I have been playing Kassadin since last season, a season in which, I mained him to get to Silver. Last season I had a greater than 60% winrate with Kass, and this season, I have a 67% winrate over 18 games. The rune updates this season have made it so that there are a lot more ways in which to build, and play Kassadin, and I hope to show you the three ways that I think are the best ways to build him. The biggest thing that makes me enjoy playing him, is the fact that he is the only assassin that is not reliant on major cooldowns. He can jump into the backline and burst multiple targets, one at a time. Unlike Talon, Zed, and more conventional assassins, that require their ultimates to be off of cooldown before they can burst a target, and when this used, they are hardly able to participate in the rest of the fight.

As this is my first guide, about the only champion that I feel that I know enough about to write a guide, any feedback is greatly appreciated!

Pros:
Best late game
Great snowball potential
Can dominate lane at and after 6 if played correctly
Best mobility
High Burst
Fairly consistent damage come full build + lvl 16
Great against AP

Cosmic Reaver

Cons:
Weak early game
Has several hard counters
Not great against AD champs
Awful against AD champs with point-and-click Crowd-Control.
Requires careful manipulation of Riftwalk stacks.

Electrocute- This is what we take when we feel confident that we are can snowball out of the laning phase. It technically scales more than Comet, but the burst that it gives at level 6 means that we take it for the early game potential. Electrocute, after the damage nerfs, and cooldown buffs is actually even better for Kassadin, as he wants it up often with less damage, rather than more damage but less often.


Arcane Comet- This is the Sorcery keystone that works best with Kassadin. It used to be that Aerie was better because it was basically a new version of Deathfire Touch, but after the nerfs to Aerie making the additional poke somewhat negligible, Comet is simply better in that it does a lot more damage, and synergizes with your E very well. Although, none of the Sorcery keystones feel that great on Kass. Taking the sorcery tree is mainly to gain access to the CDR that we need, with the mana sustain offered by the Precision tree. Arcane Comet isn't that great on Kassadin anymore, as it doesn't offer anything that isn't available in taking Fleet Footwork. I would recommend to take Fleet Footwork instead of this rune in the current META.


Sudden Impact- This is the best out of these options because it synergizes completely with Riftwalk. Cheap Shot is the next best option, but this would only be proced by your E and therefore cannot be proced as often. Taste of Blood is just a bad rune because of how long it's on cooldown, and how little it actually does heal you when it is proced.


The Ultimate Hat- Is now garbage. It is utterly useless on Kassadin with its insanely long cooldown.


Zombie Ward- Another great rune, adds a lot of vision after your wards run out, and when you kill enemy wards. This gives you a lot of safety in the laning phase, making it easier to keep tabs on who is near your lane.


Transcendence- While you will not be able to gain any additional AP through it, this rune is required to get to 40% CDR, which is a must-have on Kassadin.


Ingenious Hunter- I started using this recently, but it is definitely the best out of the options in this section. Kassadin is already so mobile that extra Movespeed is completely pointless, and Ravenous Hunter, while good, doesn't come close to the power of Ingenious Hunter. With full stacks, a 120 second cooldown, is reduced by 40%, making it a 72 second cooldown instead.


Gathering Storm- This just makes your late game that much more powerful, once again additional movespeed is unnecessary, and scorch doesn't help your early game enough to justify taking it over Gathering Storm.


Presence of Mind- This rune used to be amazing on Kassadin, now it is utterly awful. It refunds 20% of your maximum mana, if you just used all of your mana with a fully stacked riftwalk, this won't give you enough to do so again. Kassadin also has such a short cooldown on his ult that 10% reduction of that cooldown is completely useless.


Legend: Tenacity- The fact that they buffed this rune while HEAVILY nerfing Presence of Mind for Kassadin greatly saddens me. As it is, the Precision tree isn't worth taking at this point, I would recommend getting the extra CDR from the Inspiration tree instead.


Minion Dematerializer- This rune helps Kassadin a lot with his rudimentary waveclear, it will help him push the wave out so that he can base without losing too much in the process. When facing a champ with heavy waveclear this can also help to keep the wave frozen just outside the range of your turret.


Cosmic Insight- This rune is excellent because it gives you access to 5% more CDR, which allows Kassadin to riftwalk more frequently. It also allows you to teleport and flash much more frequently in combination with Ionian Boots of Lucidity.


Biscuit Delivery- This is the replacement rune for the old biscuits, giving you a potion every 3 minutes that restores a portion of your health AND mana. While this does give you some extra sustain, I don't think that this rune is better than or as good as Minion Dematerializer, which is the only rune that I would consider replacing in this tree. The Dematerializer negates the need for sustain by allowing you to base more frequently, and control the wave more easily.


Manaflow Band- Manaflow Band is what we want to take in this meta, as games are much more heavily focused around the early game Gathering Storm will not help you as much. So we take this for extra sustain in lane, and some more regeneration during the mid game.


Fleet Footwork- This is what we take to try and survive the laning phase. It was nerfed for AD champs, but for AP it was buffed, the healing on this is really nice and it synergizes with our W giving us some more damage in auto-attacking.


Dark Harvest- This is an okay rune. Not as good as Electrocute or Fleet Footwork in my opinion. It is a great scaling rune. But Kassadin doesn't need anymore help scaling, he needs help in the laning phase, which this rune does not provide.

Flash- This is a mandatory spell, helps you escape and chase. To get extra range on your Riftwalk if you want to surprise an enemy and kill them, press R then instantly flash, it almost doubles the range of your ult, and allows you to kill an enemy champion before they have time to react.


Teleport- This spell is great for Kassadin, who can be pushed out of lane fairly easily. You can back, and TP back so that you lose very little if anything at all. It also allows you to split-push and still affect teamfights very easily, make sure you use it wisely though, it's a very key summoner that has a long cooldown.


Ignite- This you can take into good match-ups. With the teleport nerfs, it is a little more in ignites favor in the snowball-y set-up. Teleport, however, is still better in other set-ups, due to the ignite damage nerfs.


Ghost- This is probably the worst summoner spell option on Kassadin, it gives you some more mobility, and that's it, you need no more mobility because Kassadin already has more mobility than any other champion in the game. The second affect is that it removes unit collision, which is what Kassadin's passive is. Ghost takes away all the benefits of taking teleport, while giving you absolutely no benefits itself.


Cleanse- This gives you some more survivability against CC heavy comps, in such a situation, I would just rush Merc Treads rather than not going teleport.


Heal/Barrier- Heal, and Barrier both take away too much while not being able to give you that much. They take away the same things as ignite, while giving you some extra protection in lane. Teleport is just better in and out of lane, they give you the ability to back more liberally and removing the need for extra protection.


Exhaust- Again, this summoner just takes away too much without having that many benefits for Kassadin.

Rod of Ages- This is the item that you want to build first on Kassadin, it gives him everything that he wants: mana, health, and ability power. This combined with the great passive that gives him mana upon losing health, and health upon using mana. Makes it the best item to get on Kass by far.


Lich Bane- This is probably my favorite item to get on Kassadin, as it makes his W the most damaging ability in his kit. It allows you to two-shot squishes, and enables you to
split-push more effectively.


Zhonya's Hourglass- A key item in any AP assassin, allows you to jump in with a full combo onto the enemy's backline, then zone the entire enemy team with the stasis provided with it. This item we either get third or second, depending on whether you need to survive longer, or need to burst down a fed carry.


Void Staff- We usually get Void Staff fourth, because in this meta, you will most often be facing tankier teams that build magic resistance by this time. However, if you are snowballing really hard, or facing a squishy team, with low magic resistance, then Rabadon's is more cost efficient at this point in the game.


Rabadon's Deathcap- This is either your fourth or fifth item based on reasons mentioned above. With this item your burst becomes truly insane, a no-stack Rfitwalk + W will bring squishes to under 50% HP.


Archangel's Staff- This item will take a longer time to charge on Kassadin compared to other champs, but it's very strong. This item will refund enough mana on riftwalks to sometimes give you up to two extra riftwalks, leading to a very powerful split-pushing item.


Liandry's Torment- Taking this item sixth is when you are facing tanky teams that you can't kill in one R+E+W+Q combo, it gives you some consistent damage and amplifies your damage when in a prolonged fight.


Morellonomicon- This item is excellent against champs with lifesteal (e.g. Warwick), or with little MR, as this item gives you flat magic penetration, this when combined with Void Staff, can make it so that you are dealing true damage to squishies.


Luden's Echo- Only 10 more AP than Hextech GLP and a passive that doesn't help Kass much, it also costs more. I would recommend just going Hextech if you really need mana, while Morello's and Liandry's are the best sixth item options.


Hextech GLP-800- This item is basically a cheaper version of Luden's with more utility, great for picking off stragglers in fights.

Kassadin's laning phase, especially pre-6 is quite weak. Before you have Riftwalk, your goal is to freeze the minion wave just outside the range of your turret, using Q to poke your lane opponent, and W for some better last-hitting.

During this time, you'll want to base when you have enough for Catalyst of Aeons and a control ward, this is not always possible though, and if you find yourself being pushed out of lane, it is far safer to base and buy a corrupting potion, a control ward, and boots if you have enough gold.

If you took the Sorcery/Inspiration runes, your goal for the laning phase is merely to farm and scale. Avoid interacting with your lane opponent as much as possible, freeze just outside the range of your turret to deny your opponent as many minions as possible, poking with Q as frequently as is sustainable.

If you took Electrocute, your goal is the same as the Sorcery runes until your hit level six, then you will want to go for 3-4 spell combos on your opponent as often as your spells are up, and your Riftwalk is not going to take all your mana. Try to wait for your E to be fully stacked, then R+E+W+Q, if you get at least the last 3 spells you will proc Electrocute and chunk your opponent to about 60% hp depending on what items you both have at this point. You will either force your opponent out of lane, or kill them if this is done correctly.

Of course, during this time, you will want to keep as much vision around your lane as possible. Try warding to the side that is most frequently pushed in to their opponent's turret (i.e. Your bot lane is Cait/Morg, their bot lane is Trist/Ali.) your bot lane will consistently be pushing, and you should ward toward their lane. Always play toward the side that you have vision/more people on. If your jungle is invading their topside jungle, but you have vision on the botside, you will still want to play toward topside to be able to respond more quickly to any opposition that your jungler will meet. If you are baiting a gank, it sometimes helps to pay away from the side that your jungler is on so that you can force your opponent to play toward the side on which your jungler is.

After the laning phase is over, you will want to coordinate with your team so that you are split-pushing in one of the side lanes. This will depend such things as what turrets are left standing, what your team wants to do, and what objectives are coming up. When split-pushing, you always want to keep as many wards as you can toward the side of the jungle you lane is on. After clearing a minion wave, go into a near brush, and wait for another wave, if two or more of the enemy team is MIA, or heading to cut you off, you need to base or run depending on how far out the opposing team is.

While teamfighting is a little awkward as Kassadin, if you have to group and teamfight, your role as Kassadin is a flanker, hiding over walls, and in bushes, to try and catch the enemy carries unaware and burst them down before they can do anything about it.

This has been my guide to Kassadin! I hope that it has been helpful and informing! Any feedback that you may have is greatly appreciated and requested, and I will be doing my best to keep this guide updated regularly!

I don't plan to give more detailed match-ups. But if you would like to see them, just tell me and I'll do my best to make them.

Dark Harvest has too long of a cooldown to be better than Electrocute.

Personally, I think that Kassadin is pretty far out of the meta right now, with bottom lane emphasizing tankiness and mobility more, and the fact that toplane is full of mobile juggernauts that can burst you far more quickly than you can burst them. Also, the fact that Kassadin doesn't get as much time to scale up really take him out of the meta at the moment.

I have changed mains in League to becoming a Fiora one-trick, as Kassadin and mid-lane were no longer enjoyable to me. That being said I feel that I have no useful information to give, so I will be archiving this guide. Thanks to all for the great support! :)