Hi this is Delorane with a build that isn't exactly meta but is done as an attempt to help deal with the continued nerfs that Kassidan has seen and will honestly most likely keep seeing as his kit makes him strong on a competitive level. I hope that you will give this off meta guide a chance and read it and give positive feed back to help me make this guide and future guides better and more cohesive.

Pros

+ Good Mobility + Decent Burst with Triforce + Muramane keeps your damage up in the late game + Good spilt pushing + Great at clean up + Snowballs easily + Sustained damage + Can stay on top of his target relatively easily

As AD Kassidan your presence as a split pusher cannot be ignored and you fare very well against most champions in a 1v1 situation being able to have a higher burst than some and just straight out sustaining others, not only that but if you get into a situation that you can't win in a straight fight you can just Riftwalk away to safety.

Cons

+ Doesn't scale the same as well into the late game as AP + Not the greatest laning phase + No AD scaling abilities + Not the best in a team fight + Alot of jumps/dashes have higher ranges than your ult + Can become useless if you fall behind

Yup you read that right almost every dash or jump in the game is either the same or has a higher range than your ult range. Also with no AD scaling abilities you are heavily reliant on landing auto attacks which is not always the easiest thing to do. And if you fall behind to far you dont have a great late game to fall back to and you pretty much become a slow cannon with Force Pulse.

• Starting off with Quints I like running with Greater Quintessence of Attack Speed as this allows you to get better trades early with the passive part of Nether Blade however Greater Quintessence of Attack Damage are also a viable option and will let you last hitter more efficiently.
• For Marks running Greater Mark of Attack Damage I found optimal so that you hit a little harder in the laning phase however both Greater Mark of Attack Speed and greater mark of hybrid penetration are viable. The attack speed marks I wouldn't recommend without taking quints of attack damage as the flat ad really helps with quick trades and last hitting. Although you are going AD you will still be doing a decent amount of magic damage do to your abilities so hybrid pen marks are a better option than straight armor pen.
• Seals are pretty much the same on all champions where Greater Seal of Armor are the standard but Greater Seal of Health are not unheard of. This mostly comes down to prefrence and to the match up. If you're up against someone like ryze health seals are probably better as the extra health with benefit you more than the extra armor but if you can only afford one I recommend armor cause even ryze will still auto attack you every once in a while.
• Glyphs are where you are going to want to cover your magic resist which give you the option of Greater Glyph of Magic Resist and Greater Glyph of Scaling Magic Resist. Now these should be decided based on you match up but I generally find that scaling is better as most AP champions want to play more passive until they hit 6 in which case the scaling magic resist starts becoming better at this point.

You want to take Flash as it will be your only form of escape pre-6 and you are very susceptible to ganks early on. Another option instead of flash is Ghost I feel as though this is better in the mid-game as it will make you not so reliant on your ult to stay on top of a target and in a bad situation you ult can still work to get you out.

Now for you second summoner spell I recommend Teleport unless you do not feel confident in you map awarness or your teams abilities to put wards in good places for you to flank. The best option in both of these situations is Ignite as it will allow you to make plays on your own in lane and be less reliant on you teammates.

Void Stone

Void stone is a really helpful passive that gives you 15% resistance to magic damage and the ability to pass through units. This will help you lane against AP champions due to the magic resist and also against most top laners who are melee as you can freely walk through the minion lines.

Null Sphere

This is a good harass tool and if used correctly can block most magic damage with the help of your passive through the laning phase. Late game on AD kassadin its mostly used to proc sheen effects and to block some of the poke that AP champions have a tendency of putting out.

Nether Blade

This is the bread and butter of AD Kassadin as it gives you a bonus 20 magic damage on every auto attack has a empowered auto attack that gives you mana and is also an auto attack reset. During the laning phase using this with a sheen will help you come out on top of most trades and will help keep your mana up so you dont need to use flask purely for mana.

Force Pulse

This helps you stick to your target like glue when combined with your ult. A one second slow may not seem like much but its enough to bridge the gap between your ults and will help you jungler get a better gank if you use it as he is coming in. This also is pretty much the only skill that remains useful no matter how far behind you are as it will allow you to peel for your carries.

Riftwalk

The scene of so many nerfs that even Irelia mains are telling riot to back off. I can't think of a single ability that has seen as many nerfs as Riftwalk sense I started playing league in season 3 however with these nerfs to the power of running AP kassadin the make AD kassadin a more viable option. With the damage of this ability scaling off of max mana a muramana can really make it hurt and the new lower mana cost means that you can use it constantly in a fight and not have to worry about the mana cost to much.

You will want to max your w as it is the ability that you will be spamming the most after your ultimate. Next you want to max your e to better stick to your target.