Kassadin is a caster isn't he? A great assassin, right? why the heck am I playing him as a DPS?!?!?
Because that's how I roll. Besides that, It works, and well.
Fact: Dps Kassadin is NOT as bursty as typical AP Kassadin.
Fact: Dps Kassadin is NOT as easy as typical AP Kassadin.
Fact: Dps Kassadin is way more fun, and in many ways better than typical AP Kassadin because:

DPS Kassadin can stay in the fight
DPS Kassadin can't be countered by getting defensive items with any sort of worth in a build, as DPS Kass shreds both Magic Resist and Armor and deals about 50% physical and 50% magical damage.

What is it that does it?

1. Kassadin's Nether Blade is the largest point in this build. I love it primarily because most people don't make much use of it in AP Kassadin. However, with a Good mix of AD/AP/AS, it can make a vicious killer.
2. End game, My DPS Kassadin build runs with almost 2.5 attacks per second, meaning the 5 seconds of Nether Blade adds enormous damage, and it's passive eliminates the need for a mana/mana regen item quite thoroughly, gaining 50 mana per second against creeps, and 150 per second against heroes.
3. Void Stone makes fighting burst mages or other casters much less dangerous than it would be for any other DPS.
4. High mobility with Riftwalk, and the mana comes back quickly once you reach enemies.

That is enough to make the build viable, and with the right items, it becomes even better.

Note: This is a jungling guide, but is fully functional outside of the Jungle. Feel free to try it either way, but I vastly prefer jungling. Much more rewarding and fun. Plus, it works!

Pros:

• Split physical and magical damage and shred, hard to counter effectively.
• No need for mana items due to Nether Blade and high attack speed.
• Good life gain due to consistent magical and physical damage as well as lifesteal/ spell vamp.
• High Mobility due to Riftwalk.
• AoE slow with Force Pulse.
• Good anti-mage due to Void Stone.
• Fun to play.

Cons:

• Susceptible to hard cc such as stuns and silences.
• Difficult early ganks vs ranged with or without Riftwalk.
• Not bursty.
• Relatively squishy if he can't fight back because most of his survivability is in lifegain.
• Early game relies on allies setting up for ganks properly. In arranged, this isn't much of a problem, but often in solo que I find allies who don't know what a ganker needs (Space away from enemy turret, targets at lower hp or mana etc.)

For summoner spells, I grab Smite and Exhaust. Smite is needed in the jungle, and Exhaust is amazing when ganking and team fighting. Alternative spells are Flash for the extra jump to get you out of sticky situations, and Ignite to help guarantee kills against champs such as vlad, trynd, or mundo.

9x Greater Mark of Attack Speed for attack speed. Ideal for the build
9x Greater Seal of Armor for additional armor to help with early jungling.
9x Greater Glyph of Magic Resist for more MR when fighting mages.
3x Greater Quintessence of Movement Speed giving mobility all game. Really comes in handy especially pre-level 6.

To start with, you will be grabbing a point in Nether Blade, and buying Cloth Armor and 5 Health Potion. There are a few things to do before we begin:

1. Do they have a jungler?
2. No

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   > Leave this list.
3. Yes

   ---

   > Where will he start?
4. Wraiths

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   > Hide in the bush further from their mid lane. When wraiths spawn, Smite one (biggest one is best) and gtfo down to your wolves, or set an ambush en route to your jungle.
5. Not Wraiths

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   > You are set. Be careful, and jungle as usual.

Pathing

I don't know how to do one of those fancy pictures that shows jungle path, so I will do a detailed list. If you dislike, I will send you half a deck of playing cards, so deal with it.
Your jungle path is important, (I have tested and used this one countless times and it works. Others may work as well, but I find this to be the best.) your targets are as follows:

Round One

• Enemy Wraiths. Spawn at 1:40, Smite the big one and activate Nether Blade right before you hit the first small one. Use a Health Potion at the start (only 1).
• Your Wolves. Activate Nether Blade right before you hit the Big Wolf (First target) and use 2 Health Potions during this fight. The big wolf will level you up. Get Null Sphere and use that on a small wolf. Kill the wolves asap.
• Your Wraiths. Smite the big one, Health Potion and Null Sphere/ Nether Blade to kill the small ones. At this point, your mana from Nether Blade solves mana issues. Period. Use your Null Sphere and Nether Blade when they are up in the jungle. 'OOM' makes you laugh, because you don't know what that is.
• Your Golems. Abilities and such to kill 1 of them. Don't use a second Nether Blade until you kill 1 and level it up. Popping Nether Blade now will allow you to kill the second Golem without needing the last Health Potion. If you feel the need, use the last one until you get used to the idea of ending the fight 2-3 hits away from death. But it works, and it is consistent.
• Recall and buy Vampiric Scepter and 1 Health Potion. If the enemy jungler started at their wraiths, you may need to wait a tiny bit or go without the second hp pot. The Vampiric Scepter is needed, the Health Potions are just a bit to help make the ganking safer.

Round 2 and Ganking

• Your Wolves. From here, Nether Blade and Null Sphere make short work of small jungle creeps. Use them to your heart's content and they die fast.
• Your Wraiths. Smite the Big one, kill the rest. When you level, grab your Force Pulse. Put stacks on it so that when you gank it is ready.
• Your Golems. Kill both, and use all remaining Health Potions.
• Ganking. Gank the nearest lane (bot if you are Purple Team, top if Blue). Make sure your allies know you are coming, and don't go in if you are just going to die. Use Force Pulse to slow, and exhaust if needed to pick up a kill. Null Sphere to stop getaways, and Nether Blade for a huge chunk of damage per hit. (+45 at this point. What? Free BF sword at lvl 4?)
• Enemy Wolves. Have caution if there is an enemy jungler. If smite is up, as you leave to recall, smite and kill the 2 small Golems at the enemy Blue.
• Recall. Buy Madred's Razors and if you can, Boots building for Berserker's Greaves

Round 3 and Roaming

• Your Golems.
• Your Red Buff. From here, Smiting targets are buff monsters, dragon, and in lane creeps. Anything else dies in 2-3 hits (4-5 for Golems). Using Force Pulse and (after you get it) rift walk while fighting buff monsters will dispatch the small guys without ever changing targets. If you are really unlucky against the Elder lizard, you will have gotten few procs of Madred's Razors and will have relatively lower hp, so be careful with ganks.
• Your Wraiths and Wolves.
• Gank mid if possible, as you now have really nice slows.
• Grab Blue buff. Same targeting as Red, be careful of hp. This is the part where unlucky hits from Madred's Razors can slow you down.
• Gank top or Mid if reasonably safe. You now have Riftwalk, and large amounts of slows.
• Recall, grabbing Berserker's Greaves and building/ grabbing Hextech Revolver if you can.
• Roam. At this point, continue with the build as is most prudent, but your life gain is very good. You have an infinite mana pool, and are an all around killing machine. It is your job to control buffs and help push lanes. Be sure to recall when needed. For the most part, however, you have most of what you need to kill things, and kill them well.

Notes:

• The current tooltip for Nether Blade is wrong on here. Actual damage per level is 30/45/60/75/90
• The current tooltip for Void Stone is wrong on here. Actual magic damage reduction is 15%.

Item Purchasing

For the most part, the items are simple, but do note that this is just an item explanation, not a buying order. That part is addressed above (look in the jungling section and item list at the top).

Berserker's Greaves are a pair of boots giving the one thing that can't go wrong in this build: attack speed (Gotta love it).

Hextech Gunblade gives all the survivability and damage output needed in a full hybrid build. Giving AP, AD, Lifesteal, and Spell Vamp. With this alone, you have almost infinite sustainability. With the amount of consistent damage you deal (both magical and physical) you have really nice life gain. The active, on top of this, is just icing on a very delicious cake (Lemon if you were wondering; I like lemon cake).

Guinsoo's Rageblade literally gives everything you want in this build. 35 AD, 93 AP, and 32% attack speed. Amazing item, really cheap comparatively; this is a bottomless glass of yummy, yummy Lemonade.

Malady is your shred item for magic damage. It gives you attack speed, a little AP, but shredding 24 Magic Resist gives a large damage increase with all of your magic damage. 20 bonus damage a hit is just salt around the rim of the Lemonade mentioned above.

Black Cleaver is your shred item for physical damage. It also gives attack speed, but shreds 45 armor and adds a hefty bit of 55 damage per hit. This adds really swell damage output and, as with all shred items, helps your teams damage as well.

Madred's Bloodrazor is amazing. You are jungling, so the initial items are very useful in early game. When you hit end game, or even mid game, you are grabbing nice attack speed and, with the 4% life per hit, you are destroying any target's health (Champion or otherwise). The damage is increased by the shred given by Malady.

Alternative items

The battlefield is a variable. There are some times that you need to change what is up. So:

• If you need more MR, I would suggest dropping Guinsoo's Rageblade for Wit's End. This will give a little bit more attack speed, as well as not crippling your damage output too much. The MR it gives, however, can be invaluable against any caster.
• If you are in the need of armor and MR, or are just getting focused down hardcore I would suggest dropping Guinsoo's Rageblade for Guardian Angel. This will allow you enough time to ult away from a sticky situation. Although it will greatly hamper your potential damage output, if needed, it can still be useful.

In the Beginning, God created Heaven, Earth, and Kassadin. And he said it was good. As such, I hope you will give Kassadin a good name as well. So to get that ball rolling, (downhill of course. Have YOU ever tried to make a ball roll up hill?) I will go into somewhat specific details about ganking, team fighting, and all around gameplay with DPS Kassadin.

Ganks

From level 4, you are ready to gank. Let your team know before hand, and ask them to start harassing and letting their lane push (specifically the nearby lane). As you don't yet have your ult, you need the enemy to have pushed farther than the halfway mark at least. When your allies are ready, get in quickly and throw your Force Pulse hitting both if possible, but the main target for sure (do not miss that). Use your Null Sphere before you get in range of your slow, especially if they are a mage. Exhaust if needed, but use Nether Blade when in melee range to wrack up the damage.

Ganking continues like this except once you have your ult, you have a gap closer. From after you can grab red buff, you will want to roam as much as you can, picking up kills/assists and pushing lanes.

Team Fights

Once team fights start, you will want to pick targets carefully. Wait for your tank to initiate, and, once the initial burst has been thrown, Riftwalk into the action and silence/slow and pick your target. Target priorities are as follows:

1. Carry- As you have lots of shred, you want the enemies sustained carry dead, and you can do this quickly. You have little burst, but they have little resistances. With Nether Blade and Hextech Gunblade active, you can make short work of them
2. Burst Mage- This is the guys who you silence, whenever it is up. When the carry is dead, the burst mage needs to fall fast. Ult for repositioning if you need to, and tear through this guy.
3. Support- That unruly Sona or Soraka isn't as much of a threat, but by now, your Nether Blade is back and the support won't know what hit them. By now, you are probably lower health so if needed ult out of the action and get to safety.

During all of this, use your ult ONLY if needed. Either to pursue an escaping enemy, or to save your life. It is important to have your ult ready in case of emergency.

Skirmishing

When you are off alone, you will find advantage in grabbing buffs for you and dragon for your team. Be ready with your ult should multiple enemies find you, but you can take most people 1v1 or even 1v2 if they have little or no hard cc. Ranged Dps such as Ashe and Caitlyn drop quickly, while a tanky-melee Dps such as Riven or Udyr are bad news, and will generally cause problems if you try to take them on 1v1. Avoid enemies like this until you know you can fight them.

When skirmishing by yourself with the enemy team, avoid anyone with lots of hard cc such as Alistar. 1v1 Against someone like him can easily turn into a 3v1 before the stuns are finished.

As far as pushing lanes goes, you can do so very easily due to Riftwalk. Remember that Nether Blade's passive will still give you mana if you are hitting a tower, so don't be afraid to ult in next to a creep wave, hit the tower for a bit, and ult away if the enemy attempts to engage.

If you feel the need, or just don't want to jungle, you can run this build in lane. It is less fun, less rewarding, and less awesome, but you can still do it. I would just start with Vampiric Scepter instead of Cloth Armor and grab Madred's Razors later, as it won't help you as much in lane.

Other than that, everything is practically the same. I would still attempt to control buffs once you get Madred's Razors however, because they can tip the game in your favor even if you are on a bad streak.

In closing, I would admonish you to try this out before you knock it, because it might hurt your knuckles. That would not be pleasant, and then you are missing out on a great fun in jungling Kassadin.
Nothing is more fun than selecting Kassadin, telling your team Dps, and selecting smite. The accompanying groans and sighs are made even sweeter when you carry your team to victory, and slice through your opponents with ease.

So remember, when you are Dps Kassadin, nether, NETHER say sorry!